CXA108 Lecture Scroll Document PDF

**[CXA108- Lecture Scroll Document ]** *[CXA108- Overview of NRV and the ADGs- Week 1]* [Nutrition Science] - Study of nutrients and other substances in foods and the body's handling of them - The foundation for Nutrition Science depends on several other sciences; including biology,...

**[CXA108- Lecture Scroll Document ]** *[CXA108- Overview of NRV and the ADGs- Week 1]* [Nutrition Science] - Study of nutrients and other substances in foods and the body's handling of them - The foundation for Nutrition Science depends on several other sciences; including biology, biochemistry and physiology - Sum total of the process involved in the taking in, and the utilisation of food substances by which growth, repair and maintenance of the body are accomplished - It involves ingestion, digestion, absorption and assimilation - Nutrients are stored by the body in various forms and drawn upon when the food intake is not sufficient - Nutrients provide the physical and metabolic basis for nearly all that we are and all that we do [Food Choices: ] - People decide what to eat, when to eat, and often in highly personal ways that are often based on behavioural or social motives rather than on an awareness of nutrition's importance to health - Many different food choices can support good health, and an understanding of nutrition will help you make sensible selections more often - Personal Preference: - Primary reason people choose food is taste -- they like certain flavours - Sweetness of sugar, savouriness of salt, liking high-fat foods - Habit - Eat cereal every morning, for example, simply because they have always eaten cereal for breakfast - Ethnic heritage or tradition - People eat the foods they grew up eating. Every country -- and, in fact every region of a country -- has its own typical foods and ways of combining them into meals - Social Interactions - Most people enjoy companionship while eating. Meals are social events, and sharing food is part of hospitality - Marketing: - Food industry and advertising persuading consumers to eat more food and more often. - Availability, convenience and economy: - People eat foods that are accessible, quick and easy to prepare, and within their financial means. Given the abundance of convenient food options, fewer adults are learning the cooking skills needed to prepare meals at home, which has its downside - People who are competent in their cooking skills eat more of their meals at home and tend to make healthier food choices - Positive and negative associations - People tend to like particular foods associated with happy occasions -- such as meat pies at football games or cake at birthday parties - Emotional comfort: - Emotions are another factor that guide food choices and eating behaviours - Some people cannot eat when they are emotionally upset - Others may eat in response to a variety of emotional stimuli -- for example, to relieve boredom or depression, or to calm anxiety - Values: - Food choices may reflect people's religious beliefs, political views or environmental concerns - People may buy vegetables from local farmers to save the fuel and environmental cost of foods shipped in from far away - They may also select foods packaged in containers that can be reused or recycled - Nutrition and health benefits: - Making healthy food choices 100 years ago was rather easy; the list of options was relatively short and markets sold mostly fresh, whole foods - Today, tens of thousands of food items fill the shelves and most items are processed - Whether a processed food is a healthy choice depends in part, on how extensively the food was processed - When changes are minimal, processing can provide and abundant, safe, convenient, affordable, and nutritious product The Six Classes of Nutrients Nutrient Organic Inorganic Energy Yielding Macronutrient Micronutrient --------------- --------- ----------- ----------------- --------------- --------------- Carbohydrate Yes No Yes Yes No Lipids (fats) Yes No Yes Yes No Proteins Yes No Yes Yes No Vitamins Yes No No No Yes Minerals No Yes No No Yes Water No Yes No No No [Nutrients and you -- How do we know if we are getting enough nutrients ] - Foods contain a chemical composition of organic (PRO, CHO, FAT, VIT) and inorganic (MIN, H2O) compounds - We do not eat ENERGY; we derive energy from eating carbohydrates, fat and protein [Energy From Foods ] - Energy is measured in kilojoules (kj) or kilocalories (kcal or CAL); - 1 kcal = 4.2 kJ. Nutrient Energy (kJ/g) Energy (kcal/g) -------------- --------------- ----------------- Carbohydrate 17 4 Protein 17 4 Fat 37 9 [Nutrient uses in the Human body] - Provide energy: carbohydrate, proteins, lipids - Activity in the body is fuelled by food as energy is released from bonds within carbohydrate, fat and protein as they are broken down - Excess energy is stored in the body as compounds such as body fat - Promote growth and development - Proteins, lipids, vitamins, minerals, water - Water, vitamins and minerals do not provide energy and are known as micronutrients because the body needs them in smaller quantities - Most foods contain a mix of macro- and micronutrients [Calculate Energy Available from Foods ] - Calculate energy available from a food, multiply number of grams of Carbohydrate, Protein, and Fats by 17,17, and 37 respectively - For example: 1 slice of bread with 1 tablespoon of peanut butter on it contains 16 grams carbohydrate, 7 grams protein, and 9 grams fat: - Step 1: 16g carbohydrate by 17 kJ/g = 272 kJ - Step 2: 7g protein by 17 kJ/g = 119 kJ - Step 3: 9g fat by 37 kJ/g = 333 kJ - Step 4: Add steps 1-3 together = 742 kJ [Using Energy Density of Foods to Eat Less ] - Energy density is a measure of kJ content of food per gram. - Choosing foods low in energy density can give similar feelings of fullness to higher energy dense foods, but without the extra kJ [The Nutrient Reference Values] - Nutrition experts, using results of thousands of studies, produced set of standards that define amounts of energy, nutrients, other dietary components and physical activity that best support health - Nutrient Reference Values (NRV): - Recommended Daily Intake (RDIs) - Estimated Average Requirements (EARs) - Average Intake (AI) - Upper level of Intake (UL) - Suggested Dietary Targets (SDTs) [Nutrient Reference Values (NRVs) -- terms & their abbreviations ] - EER -- Estimated Energy Requirement - AMDR Acceptable Macronutrient Distribution Ranges - EAR -- Estimated Average Requirement - RDI -- Recommended Dietary Intake - AI -- Adequate Intake - UL -- Upper Level (of intake) [Establishing Nutrient Recommendations ] - Estimated Average Requirement (EAR) - defines the requirement of a nutrient that supports a specific function in the body for ½ of the healthy population. - Recommended Dietary Intake (RDI) - uses the EAR as a base and include sufficient daily amounts of nutrients to meet the known nutrient needs of practically all healthy populations. This recommendation considers deficiencies. - Adequate Intakes (AI) - reflect the average daily amount of a nutrient without an established RDI that appears to be sufficient. - Upper Level of Intake (UL) - is a maximum daily amount of a nutrient that appears safe for most healthy people and beyond which there is an increased risk of adverse health effects. [Establishing Energy Recommendations] - Estimated Energy Requirement (EER) represents the average daily energy intake to maintain energy balance and good health for population groups. - Acceptable Macronutrient Distribution Range (AMDR) represents the range of intakes for energy nutrients that provide adequate energy and nutrients and reduce risk of chronic disease. - 45--65 per cent kilojoules from carbohydrate. - 20--35 per cent kilojoules from fat. - 15--25 per cent kilojoules from protein. [Using Nutrient Recommendations ] 1. Estimates of adequate energy and nutrient intakes apply to healthy people 2. Recommendations are not minimum requirements, nor are they necessarily optimal intakes for all individuals 3. Most nutrient goals are intended to be met through diets composed of a variety of foods whenever possible. 4. Recommendations apply to average daily intakes. 5. Each of the NRV categories serves a unique purpose [Nutrition Assessment ] - With a deficiency of energy, the person may display the symptoms of undernutrition by becoming extremely thin, losing muscle tissue and becoming prone to infection and disease. - With a deficiency of a nutrient, the person may experience skin rashes, depression, hair loss, bleeding gums, muscle spasms, night blindness or other symptoms. - With an excess of energy, the person may become obese and vulnerable to diseases associated with overnutrition, such as heart disease and diabetes. With a sudden nutrient overdose, the person may experience hot flushes, yellowing skin, a rapid heart rate, low blood pressure or other symptoms. - Similarly, over time, regular intakes in excess of needs may also have adverse effects [Nutrition Assessment of individuals] - Evaluates that many factors that influence or reflect nutritional health. - Historical information: regarding diet, health status, drug use and socioeconomic status is gathered - Anthropometric data: measure physical characteristics including height and weight - Physical examinations: require skill and reveal possible nutrition imbalances - Laboratory tests: detect early signs of malnutrition [Nutrition Assessment of Populations ] National Nutrition Surveys: - National Nutrition Monitoring Program uses survey research to collect data on foods people eat and people's health status - Data collected is used for nutrition policy, food assistance programs and food supply National Trends: - Shows an increased intake of fast food, increased portion sizes and an increased consumption of energy-dense foods and drinks - This intake is associated with an increased risk for overweight and obesity [Diet and Chronic Diseases ] - Diet has always played a vital role in supporting health - Nutrition research now focussed on chronic diseases associated with energy and nutrient excess - Once thought to be a 'rich countries' problem is now becoming epidemics in developing countries - Contributes to 5 out of 10 top causes of death [Factors Contributing to Deaths and Disease Burden ] - Smoking, poor dietary habits, physical inactivity and alcohol consumption are personal behaviours that can be changed. - Decisions to not smoke, to eat a wellbalanced diet, to engage in regular physical activity and to drink alcohol in moderation (if at all) improve the likelihood that a person will enjoy good health. - Australian Guide to Healthy Eating and Australian Dietary Guidelines have been developed to help individuals determine what constitutes a healthy diet that will help lower disease risk [Nutrition Information and Misinformation] - Nutrition on the internet: - Internet information can be published by ANYONE. - May be high-quality information: PubMed. - May be misleading, incomplete and inaccurate. - Nutrition in the News: - Can be misleading and contradictory. - May report scientific findings prematurely. - Identifying nutrition experts: dietitians and nutritionists. - Members of relevant dietetics or nutrition organisations such as Dietitians Australia. - https://dietitiansaustralia.org.au/ to find an Accredited Practising Dietitian [Planning a healthy diet ] - Food choices over years influence the body's health, consistently poor choices increase risks of developing chronic diseases - Ideally, need to create a diet that supports health - Fortunately, most foods provide several nutrients - Wise diet-planning is to select a combination of foods that deliver a full array of nutrients [Diet-planning principals ] 1. Adequacy (dietary) - providing sufficient energy and essential nutrients for healthy people. - Adequacy means that the diet provides sufficient energy and enough of all the nutrients to meet the needs of healthy people. 2. Balance (dietary) -- consuming the right proportion of foods. - The art of balancing the diet involves consuming enough -- but not too much -- of each type of food. 3. Energy (kilojoule) control -- balancing the amount of foods and energy to sustain physical activities and metabolic needs. - Designing an adequate diet without overeating requires careful planning. Once again, balance plays a key role. The amount of energy coming into the body from foods should balance with the amount of energy being used by the body to sustain its metabolic and physical activities. 4. Nutrient density -- measuring the nutrient content of a food relative to its energy content. - To eat well without overeating, select foods that provide the most nutrients for the least food energy (kilojoules). 5. Moderation (dietary) -- providing enough but not too much of a food or nutrient. - Foods rich in fat and sugar provide enjoyment and energy but relatively few nutrients. In addition, they promote weight gain when eaten in excess. 6. Variety (dietary) -- eating a wide selection of foods within and among the major food groups. - A diet may lack variety, if a person eats the same foods day after day. People should select foods from each of the food groups daily and vary their choices within each food group from day to day. Different foods within the same group contain a different array of nutrients. For example, strawberries are especially rich in vitamin C while apricots are rich in vitamin A. - Variety improves nutrient adequacy [Comparing Foods on Nutrient Density ] - To eat well without overeating, select foods that provide the most nutrients for the least food energy (kJ) - 40 grams of cheddar cheese = 960. 300mg calcium/960 kJ = 0.3 mg per kJ - 1 cup of low-fat milk = 480 kJ 300mg calcium/480 kJ = 0.6 mg per kJ - The low-fat milk, is twice as calcium dense as the cheddar cheese -- it offers the same amount of calcium for half the kilojoules. - Both foods are excellent choices for adequacy's sake alone, but to achieve adequacy while controlling kilojoules, the low-fat milk is a good choice. [Diet-Planning Guides ] - To plan a diet that achieves all the dietary ideals, a person needs tools as well as knowledge. - Most widely used tools for diet planning are food group plans that build a diet from clusters of foods that are similar in nutrient content. - Selecting foods from each of the groups eases the task of creating an adequate and balanced diet. - The Australian Dietary Guidelines (ADGs) encourage consumers to adopt a balanced eating plan. The Australian Guide to Healthy Eating (AGTHE) assigns foods to five major groups and recommends daily amounts of foods from each group to meet nutrient needs. - In addition to presenting the food groups, the AGTHE lists the most notable nutrients of each group, the serving equivalents and the foods within each group sorted by nutrient density. 1. Recommended amounts - All food groups offer valuable nutrients, people should make selections from each group daily 2. Notable Nutrients - Each food group contributes key nutrients - Provides flexibility, person can select any food from a food group and receive similar nutrients 3. Nutrient Density - Provides foundation for healthy diet emphasising nutrient-dense options within each food group 4. Serving Equivalents - Cups are used to measure servings of fruits, vegetables and milk. - Grams are used to measure servings of grains and meats. - Visualisation with common objects can be used to estimate portion sizes. [The Australian Guide to Healthy Eating ] Age Vegetable and legumes/beans Fruit Grain (Cereal) Lean Meats, Poultry, fish Dairy Approximate number of additional serves ----------- --------- ----------------------------- ------- ---------------- --------------------------- ------- ----------------------------------------- Men 19-50 6 2 6 3 2 ½ 0-3 51-70 5 ½ 2 6 3 2 ½ 0-2 ½ 70+ 5 2 4 ½ 2 ½ 3 ½ 0-2 ½ Women 19-50 5 2 6 2 ½ 2 ½ 0-2 ½ 51-70 5 2 4 2 4 0-2 ½ 70+ 5 2 3 2 4 0-2 Pregnant (19-50) 5 2 8 ½ 3 ½ 2 ½ 0-2 ½ Lactating (19-50) 7 ½ 2 9 2 ½ 2 ½ 0-2 ½ [From Guidelines to Shopping Trolley ] Emphasise nutrient-rich foods such as: - Wholegrains - Fruits and Vegetables - Lean meats - Fish - Poultry - Low-fat milk products - You can design such a diet for yourself, but how do you begin? Start with the foods you enjoy eating. Then try to make improvements, little by little. - When shopping, think of the food groups and choose nutrient-dense foods within each group. - Be aware that many food items are processed and nutrient-poor. - Fortified foods have improved nutrition. [From Guidelines to Groceries ] Breads and cereals: - Refined products may have lost many nutrients - Enriched products may have had vitamins and minerals added - Wholegrain products are high in fibre and support good health and should comprise the majority of bread and cereal choices Vegetables: - Can be fresh, frozen, or canned - Aim to choose those without fat or salt - Good sources of vitamins and minerals - Legumes are also a great low-fat, high-fibre option Fruits: - Choose fresh, whole fruits where possible - Good source vitamins, minerals, phytochemicals and fibre Meat, fish and poultry: - Provide essential minerals; e.g. iron - 120g raw meat = 100g cooked meat - Try cooking without added fats - Trim visible fat or buy lean cuts Milk: - Choose low-fat options - Low-fat milk contains approx. 1.5% or 1.5g fat per 100ml - Milk can be fortified with vitamin A and D, and with omega oils - Non-dairy alternatives i.e. soy milk may be fortified *[CXA108- Digestion, Absorption and Transport of Nutrients- Week 2]* [Digestion and Absorption] - Digestion is body's ingenious way of breaking down foods into nutrients in preparation for absorption 1. Human beings breathe, eat and drink through their mouths 2. Contents should be kept moving forward, slowly but steadily, at a pace that permits all reactions to reach completion 3. To move through the system, food must be lubricated with fluids 4. Digestive enzymes must break food down 5. Cells of the digestive tract need protection against the action of the powerful digestive juices that they secrete 6. Once residual matter has reached the end of the GI tract, it must be excreted, but this function must be controlled [The Muscular Action of Digestion] - Two layers of muscle in the Gi tract coordinate to produce two different kinds of action - Inner circular muscles - Outer longitudinal muscles - Segmentation: Inner circular muscles contract and relax in a way that churns the chyme muscles tightening and relaxing, pushing food along the GI tract - Peristalsis: Outer longitudinal muscles contract rhythmically in a way that moves chyme forward [Stomach and Sphincter Muscle ] - Stomach has thickest walls and strongest muscles of all the GI tract organs - Third layer of diagonal muscles that also alternately contract and relax - Three sets of muscle work to force the chyme downwards, but the pyloric sphincter usually remains tightly closed, preventing the chyme form passing into the duodenum of the small intestine - Sphincter muscles periodically open and close allowing contents of the Gi tract to move along at controlled pace - Oesphageal sphincter: prevent reflux of stomach contents. - Pyloric sphincter: controls release of stomach contents into SI. - Ileocaecal valve: controls release of SI contents into LI. [Secretions of Digestion ] - The breakdown of nutrients requires different secretions from five different organs. - Including water and variety of enzymes. - An enzyme facilitates a chemical reaction either: - Catalyst -- increases rate of reaction without itself being changed. - Hydrolysis -- add H2O (hydro) to break (lysis) into smaller pieces. - Digestive enzymes are identified by the organ they come from and the compounds they work on. - Gastric lipase: origin stomach -- breaks down lipids. - Pancreatic lipase: origin pancreas -- also breaks down lipids. - Due to these secretions, carbohydrate, fat and protein are digested in the small intestine [Secretions of Digestion and Major Actions] Organ or Gland Target Organ Secretion Action ------------------- ----------------- ------------------ ----------------------------------------------------------------------------------------------------------------------- Salivary glands Mouth Saliva Fluid eases swallowing; salivary enzyme breaks down some carbohydrate Gastric glands Stomach Gastric juice Fluid mixes with bolus; hydrochloric acid uncoils proteins; enzymes break down proteins; mucus protects stomach cells Pancreas Small intestine Pancreatic Juice Bicarbonate neutralises acidic gastric juices; pancreatic enzymes break down carbohydrate, fats and proteins Liver Gall bladder Bile Bile is stored until needed Gall bladder Small intestine Bile Bile emulsifies fat so that enzymes can have access to break it down Intestinal glands Small intestine Intestinal Juice Intestinal enzymes break down carbohydrate, fat and protein fragments; mucus protects the intestinal wall [Role of the Stomach and Gastric Juice ] - Gastric glands secrete gastric juice -- H2O, enzymes, HCI - Primarily protein digestion - Strong acidity of the stomach kills most bacteria entering the body with food - To protect the stomach from this acidity, cells secrete mucous that coats the lining of the stomach - Can cause the sensation of heartburn if it happens to reflux into the oesophagus - Gastroesophageal reflux disease (GERD) is example of chronic digestive disease - Acid inactivates salivary enzymes [Role of Pancreatic Juice and Bile] - Pancreatic ducts lead into the duodenum. - Pancreatic juice contains enzymes that act on all macronutrients. - Pancreatic juice also contains sodium bicarbonate which is alkaline -- this neutralises the acidic chyme entering from the stomach. - Bile (produced in liver, stored in gallbladder) also is released into duodenum. - Gallbladder squirts bile into SI in presence of fat. - Bile is not an enzyme but an emulsifier that enables fat to be suspended in water so that enzymes may act on it [Final Stage of Digestion ] - Energy-yielding nutrients are disassembled for absorption. - Vitamins, minerals and water do not need disassembling. - Undigested residues, including some fibres, continue through the digestive tract and form the stool. - They may serve as substrates for bacteria that inhabit the SI. - The enormous surface area of the 6 metre small intestine facilitates nutrient absorption. - Meal digestion time can vary = three to four hours. - Most CHO (simple sugars) and PRO absorbed very quickly \~30 mins. - Fatty meal absorbed very slowly \~4-8 hours [Absorption of Nutrients ] - Absorption takes place in the small intestine - Cells are specialised to absorb different nutrients [Anatomy of the Absorptive system] - The inner surface of the small intestine looks smooth and slippery, but when viewed through a microscope, it turns out to be wrinkled into hundreds of folds - Each fold is contoured into thousands of finger-like projections -villi - A single villi is composed of hundreds of cells and each is covered with its own microscopic hairs, called microvilli. - Villi are in constant motion - Villus lined by a thin sheet of muscle, so it can wave, squirm and wriggle like the tentacles of a sea anemone. - Any nutrient molecule small enough to be absorbed is trapped among the microvilli [Small Intestine ] - Each cell of a villus is coated with thousands of microvilli, which project from the cell's membrane. - Crevices between vili are Crypts -- secrete intestinal juice. - Goblet cells secrete mucous. - Hundreds of different enzymes and 'pumps' lie in the microvilli and membrane and act on different nutrients. [The Circulatory System ] - Vascular system is a closed system of vessels, with the heart serving as the 'pump'. - All body tissues derive oxygen and nutrients from the blood. - The digestive system supplies the nutrients to be picked up. - The returning blood leaves the digestive system via the hepatic portal vein, which leads to the liver, before returning to the heart via the hepatic vein. [The Liver] - The liver has a key role in nutrient transport. - Its placement means it is the first organ to receive nutrients absorbed from GI tract. - The liver is the body's major metabolic organ. - The liver detoxifies substances to protect the body. - Vulnerable to damage (alcohol) and to viruses such as hepatitis. - Water-soluble nutrients and small products of fat digestion are released to the bloodstream and travel to the liver where their fate and destination will be determined. [The Lymphatic System] - The lymphatic system is the one-way route for fluid from the tissue spaces to enter the blood. - It has no pump; instead, lymph circulates between the cells of the body and collects into tiny vessels. - Lymph collects in the thoracic duct behind the heart, where the lymph enters the bloodstream via the subclavian vein. - Fat-soluble vitamins and larger fats form chylomicrons and are released to the lymphatic system where they travel slowly and enter back into the bloodstream bypassing the liver initially [Health of the GI Tract ] - Many factors influence the health and regulation of the GI tract. - Age, diseases and malnutrition can affect functioning. - Dietary pattern and intake can affect GI bacteria. - The health of the GI tract may contribute to obesity and inflammatory bowel disease. - Ongoing research is trying to determine exactly how bacteria that live in the GI tract might contribute to the development of obesity and other metabolic diseases. [Microbiota/Microbiome] - A healthy GI tract is home to \~100 trillion microbes, collectively known as the human microbiome. - Bacteria, viruses, fungi, protozoa, microorganisms - The prevalence of different microbes in various parts of the GI tract depends on such factors as pH, peristalsis, diet and other microbes. - Recent research has revealed that a person's health reflects the relative stability, disturbance, and resilience of the microbiome. - Changes in microbiota composition and activity are associated with dozens of common diseases, such as irritable bowel syndrome (IBS) and obesity. - Number and kinds of GI microbes differ in non-obese and obese individuals; the population of microbes in obese people with more body fat is less diverse than in non-obese people. [Pre- and Pro-biotics] - Microbiome is extremely dynamic -- influenced by factors i.e. age, diet, hormonal cycles, travel, medications (antibiotics), and illness. - Prebiotics are foods that not absorbed but used as food to promote growth of healthpromoting species of intestinal bacteria. - garlic, onion, chicory root, artichokes, asparagus, barley, wheat, tomatoes, leeks and bananas, soybeans, chickpeas, field peas, green peas, lentils, mung, lima and navy beans. - Probiotics are live bacteria found in foods such as yoghurt. Can be beneficial to health as they increase number of good bacteria. - The potential GI health benefits of probiotics include: - helping to alleviate diarrhoea or constipation, inflammatory bowel disease, ulcers, allergies and lactose intolerance - enhancing immune function and protecting against colon cancer. [Regulation of the GI Tract ] - Ability of digestive tract to handle its ever changing contents illustrates the principle of homeostasis. - The hormonal (endocrine) system and the nervous system coordinate all digestive and absorptive processes. - The GI tract stimulates or inhibits secretions with hormones and nerve-pathway 'feedback mechanisms' to maintain homeostasis. - Pancreatic secretions change based on the content of the diet. - A rapid change to a typical diet can often result in 'upset stomach' due to a lag in pancreatic secretion change. [Intestinal Feedback Mechanism] Stomach maintains pH of 1.5 -- 1.7: - Food enters stomach -- stimulates cells to release hormone gastrin - Gastrin stimulates cells to secrete components of HCI - When pH 1.5 is reached the acid turns off the gastrin-producing cells - The cells releasing gastrin and the glands stop producing HCI Pyloric sphincter opens to let out chyme then closes again - When pyloric sphincter relaxes acidic chyme slips through. - Cells of the pyloric muscle sense the acid and cause pyloric sphincter to close tightly. - After acidic chyme has been neutralised by pancreatic bicarbonate and the juices surrounding the pyloric sphincter have become alkaline will allow the pyloric sphincter relax again. - Ensures that chyme will be released slowly enough to be neutralised as it flows through the SI. - Important as less mucous coating the SI than stomach -- not protected from acid. - Pancreatic enzymes will not work in acidic environment. Pancreas adds bicarbonate to chyme entering SI - Presence of chyme stimulates wall of duodenum to release hormone secretin into the blood. - When secretin reaches pancreas it stimulates release of bicarbonate-rich juices. - Occurs whenever presence of acid stimulates secretin. - After the acid has been neutralised, the cells of the duodenum are no longer stimulated -- secretin is not release into the blood and the pancreas stops releasing bicarbonate-rich juices. Pancreatic secretions contain mix of enzymes to digest CHO, LIPID and PRO. - Pancreas secretes enzymes tailored to the nutrients ingested over the last several days. - Predominantly CHO -- then most secretes amylase. - Predominantly FAT -- then most secretes lipases. - Though that hormones secreted from the GI tract keep the pancreas informed to enzymes required. - May explain why sudden dietary changes cause can 'upset digestion.' Why don't digestive enzymes damage the pancreas. - Pancreas protects itself by secreting inactivate enzymes. - These proteins are released into the SI where they are activated to become enzymes. - Pancreatitis -- digestive enzymes become active inside the infected pancreas, causing inflammation and damage to pancreatic tissue. How does the gall bladder know when to release bile. - Fat in SI stimulates intestinal wall to release hormone cholecystokinin (CCK). - CCK travels in blood to gall bladder -- stimulates it to contract releasing bile in SI. - Stimulates pancreas to release bicarbonate and enzymes into SI. - Once fat is emulsified and enzymes have begun to work on the fat in the GI tract no longer causes the release of CCK. - Bile can still be released from the liver directly to the SI even if a diseased gall bladder is removed. When fat or protein is present intestinal motility slows -- how does the intestine know to slow down - In addition to CCK stimulating release of bile to aid in fat emulsification -- also slows GI tract motility. - Slowing down of digestive process helps maintain a pace that allows all reactions to be completed. [The Primary Actions of GI Hormones ] Hormone Responds to Secreted from Stimulates Response ----------------- --------------------------------------- ----------------- ----------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Gastrin Food in the stomach Stomach wall Stomach glands Hydrochloric acid secreted into the stomach to maintain and acidic pH Secretin Acidic chyme in the small intestine Duodenal wall Pancreas Bicarbonate-rich juices secreted into the small intestine to maintain a slightly alkaline pH Cholecystokinin Fat or protein in the small intestine Intestinal wall Gall bladder Pancreas Bile secreted into the duodenum to emulsify fats. Bicarbonate- and enzyme-rich juices secreted into the small intestine to maintain a slightly alkaline pH, digest fats and proteins and slow GI tract motility [The System At its Best ] - Healthy diet promotes healthy GI tract and optimal nutrient absorption; too much can be harmful. - Life-span of enterocytes averages around 72 hours. - Health of GI tract affected by; - Sleep -- allows for repair and maintenance of tissue and removal of wastes that might impair functioning. - Physical activity -- promotes good GI muscle tone. - State of mind -- stress alters GI motility, secretions, permeability, blood flow and bacteria. - Types of foods eaten also have an effect of GI health. *[CXA108- Carbohydrates - Week 3]* [Overview: Carbohydrates ] - Carbohydrates (glucose) provides nearly all of the energy the human brain uses daily - Glycogen (the storage form of carbohydrate) provides about half the energy that muscle and other body tissues use. - The other half of the body's energy comes mostly from fat - All plant foods, wholegrain, vegetables, legumes, fruits and milk products contain carbohydrate - Wholegrain foods, vegetables, legumes and fruits deliver carbohydrate and fibre with valuable vitamins and minerals. - Milk products typically lack fibre, but they provide carbohydrate along with vitamins and minerals. [The Chemist's View ] - Carbohydrate are made of: - Carbon atoms, - Hydrogen atoms, - Oxygen atoms - These atoms form chemical bonds that follow the laws of nature - Simple Carbohydrate - Complex Carbohydrate [Simple Carbohydrates: Monosaccharides] - Monosaccharides are single sugars (most are hexoses). - Glucose serves as the essential energy source and significant in nutrition -- is commonly known as blood sugar. - Fructose is the sweetest. It occurs naturally in honey/fruits, added to many foods i.e. soft-drinks/deserts and those imported in the form of high-fructose corn syrup. - Galactose rarely occurs naturally as a single sugar. [Carbohydrates: Chemical Reactions ] - Condensation reactions link monosaccharides together - Hydrolysis reactions split molecules [Simple Carbohydrates: Disaccharides] - Disaccharides: pairs of monosaccharides, one is always glucose - Maltose = two glucose units, produced during the germination of seeds and fermentation. - Sucrose = glucose and fructose. It is refined from sugar cane and sugar beets, tastes sweet and is readily available. - Lactose = glucose and galactose combined. It is found in milk and milk products. [The Complex Carbohydrate ] - Compared to simple sugars -- complex carbohydrates contain many units together. - Few (oligosaccharides) or many (polysaccharides) glucose units bound/linked together in straight or branched chains. - Glycogen: - Storage form of glucose in the body. - Provides a rapid release of energy when needed. - Starches: - Storage form of glucose in plants. - Found in grains, tubers and legumes. - Fibre: - Soluble and insoluble. [Dietary Fiber] - Bonds in these polysaccharides can't be broken in the GI tract, so they pass through the body and contribute little to no energy [Fibre ] - Fibre is often sorted into two groups based on their solubility which helps to explain their actions in the body - Soluble fibre: dissolves in water (Oats, barley, legumes, citrus fruits) - Form gels: viscous - Easily digested by bacteria in colon: fermentable - Protects against Heart disease and Diabetes by lowering blood cholesterol and glucose levels. - Insoluble fibres: does not dissolve in water (wholegrains i.e. bran and vegetables - Does not form gels: non-viscous - Not easily digested by intestinal bacteria - Promotes bowel movements and alleviated constipation - Resistant starches escape digestion and are found in legumes, raw potatoes and unripe bananas - Phytic acid or phytate has a close association with fibre and binds some material [Examples of Specific Fibre Products] B-Glucans: - Reported effectiveness in reducing serum cholesterol and postprandial glucose concentrations. - Foods with highest source - Cereal brans: i.e. oats and barley Psyllium: - Used as laxative in products such as Metamucil - Must ingest plenty of fluids with psyllium as constipation/chocking may result if it is not ingested with adequate fluids. [Lactose Intolerance ] - Lactase needed for lactose breakdown -- highest activity after birth, with only \~30% of population have efficient lactase activity as adults. - \~90% East Asian, West African, Arab, Jewish, Greek, and Italian descent. - \~5% Northern European descent are lactose intolerant. - Symptoms: undigested lactose in GI attracts water leading to bloating, abdominal discomfort, diarrhoea. Becomes food for bacteria producing more gas. - Causes: lactase deficiency declines with aging, intestinal villi damaged by disease, medications, prolonged diarrhoea and malnutrition. - Management can include: - Increasing consumption of milk products gradually. - Mixing dairy with other foods. - Spreading dairy intake throughout the day. - Use of acidophilus milk, yoghurt. [Carbohydrate Metabolism] - Major role of carbohydrate is to provide glucose for energy. - Most cells rely upon glucose for fuel source. - Glycogen is storage form in body. - Liver stores \~ ⅓ glycogen: releases into blood when needed. - Muscle stores \~ ⅔ glycogen: uses supply for itself during exercise. - Glycogen is stored with water; therefore bulky and limited amount able to be stored. - In absence of dietary CHO -- liver glycogen is depleted in \~18 h. - Comparison of \~2 month fuel supply stored as fat. - Glycogen found in meats -- we don't consume any glycogen. - Preferred energy source for brain, nerve cells, red blood cells - Protein can make glucose -- fat can't be used to make glucose - If glycogen stores depleted -- body protein will be used for glucose - Gluconeogenesis is the conversion of a non-carbohydrate source to glucose. - If glycogen stores are depleted, the body makes glucose from protein - Protein-sparing action is having adequate carbohydrate in the diet to prevent the breakdown of protein for energy - Inadequate carbohydrate intake will result in a change in fat metabolism pathways for energy. - Fat broken down in the liver in absence of CHO can make ketone bodies (acids) in the blood. - Brain and muscle can use ketone bodies as an energy source. - Important fuel source in starvation. - Elevated ketone bodies in the blood upsets the acid-base balance in the body -- ketosis. - To spare body protein and prevent ketosis, body needs at least 50-100 grams CHO/day. - Conversely, the body can also use glucose to make body fat when carbohydrates are consumed excessively. [Glucose Homeostasis] - Blood glucose must be constantly maintained to nourish cells - Low blood glucose may cause dizziness and weakness - High blood glucose may cause fatigue - Extreme fluctuations can be fatal - Glucose and hormone control [Falling Outside the Normal Range ] - Failure of glucose homeostasis = diabetes or hypoglycaemia Diabetes - Type 1 diabetes is the less common type with no insulin produced by the body. - Type 2 diabetes is the more common type where fat/muslce cells resist insulin. - Prediabetes is blood glucose that is higher than normal but below the diagnosis of diabetes. - Hypoglycaemia is low blood glucose and can often be controlled by dietary changes. [Glycaemic Response ] - Glycaemic response is how quickly the blood glucose rises and elicits an insulin response. - Slow CHO absorption: modest rise in blood glucose, returning to normal smoothly = Low Glycaemic Response. - -- Fast CHO absorption: rapid surge in blood glucose, undesirable return to normal = High Glycaemic Response. - Glycaemic index: classifies foods according to their potential for raising blood glucose. - Glycaemic load: refers to a food's glycaemic index and the amount of carbohydrate the food contains. - The benefit of the glycaemic index is controversial. - Most healthy foods are naturally low GI. [Health effects of Sugar ] - The use of added sugars has risen steadily over the past several decades, with soft drinks and sugared fruit drinks accounting for most of the increase - In moderate amounts, sugars add pleasure to meals without harming health In excess, however, they can be detrimental in two ways: 1. Sugar can contribute to nutrient deficiencies by supplying energy (kJ) without providing nutrients 2. Sugars contribute to tooth decay - Obesity and chronic disease: Over the past several decades, as obesity rates increased sharply, consumption of added sugars reached an all-time high. - Nutrient deficiencies: Foods that contain large amounts of added sugar, such as cakes, lollies and soft drinks, deliver glucose and energy with few, if any, other nutrients. [Artificial Sweeteners ] - Artificial sweeteners can also be called 'non-nutritive sweeteners' because they provide no energy - Can assist with weight control - Do not impact blood glucose levels - Saccharin \[Sugarine\]: 0kJ/g - Rapidly absorbed and excreted. - Aspartame (phenyalanine and aspartic acid) \[Equal\]: 16kJ/g - Digested and absorbed. - Sucralose \[Splenda\]: 0kJ/g - Not digested or absorbed. - Acesulfame potassium: 0kJ/g - Not digested or absorbed. - Cyclamate: 0kJ/g - Incompletely absorbed. - Stevia \[herbal\]: 0kJ/g - Digested and absorbed [Sugar Alcohols ] - Sugar alcohols: (occur naturally in fruit/veg, added to processed foods) - Maltitol (8.5kJ/g), mannitol (6.7kJ/g), sorbitol (11kJ/g), xylitol (10kJ/g), isomalt (8kJ/g) and lactitol (8kJ/g) - Absorbed more slowly and metabolised different in the body - Low glycaemic response - Side effects include Gi discomfort [Recommended Intakes of Sugars ] - Because added sugars deliver energy but few or no nutrients: ADG - Urge consumption of only a moderate amount of sugars and food containing added sugar Australian Health Survey: Consumption added sugars 2011-12 - Australians consumed 60g free sugars/day (14 teaspoons) - Highest among teenage males (14-18 years), 92 g/day (22 tsp) - \~50% of all Australians \>2 yrs and over exceeded the WHO recommendation to limit energy from free sugars to less than 10% of dietary energy. - EXAMPLE: 600 ml Coca Cola containing 1,080 kJ. - Little value from this drink as no other nutrients contained. - 63.6 g sugar or 15 tsp. - Contrast: 3 slices of whole grain bread containing 1,100 kJ. - Contains \~12 g protein and \~7 g dietary fibre. - Most of the vitamins and minerals. [Health Effects of Starch and Fibre ] - A diet that provides abundant CHO (45-65% energy intake) best supports good health -- AMDR. Daily intake of whole grains, vegetables, legumes and fruits - May offer some protection from heart disease and stroke. - Helps with reducing risk of Type 2 diabetes. - Enhances GI health of LI, which can then block the absorption of unwanted particles. - May protect against colon cancer by removing potential cancer-causing agents from the body. - Helps with weight management, high-fibre and wholegrain foods low in fat/added sugars thus promote weight loss by delivering less energy. [Health Effects of Dietary Fibre ] [Harmful Effects of Excessive Fibre Intake ] - Person with small stomach capacity eating high fibre diet may not take in enough energy or nutrients to meet demands. - A sudden high-fibre diet can cause temporary abdominal discomfort, gas and diarrhoea. - Increase fibre intake gradually to give GI tract time to adjust. - Drink plenty of fluids to soften the dietary fibre. - Variety of sources -- vegetables, fruits, legumes and wholegrains. - Some dietary fibre can limit absorption of nutrients by speeding up transit time and by binding minerals. - When mineral intake is adequate a reasonable intake of high-fibre doesn't compromise mineral balance. [Recommended Intakes of Starch and Fibres ] - Importance of CHO as essential energy source; there is no specific recommendation of amount required daily. - Australian Dietary Guidelines recommends plenty of grains (cereals), preferably wholegrain -- aim for \~ 6 serves daily. - NRVs have an Adequate Intake (AI) for fibre: - 30 g/day for men (19 years and older). - 25 g/day for women (19 years and older). - Australian Guide to Healthy Eating recommends several servings of fruits, vegetables, legumes daily as best way of achieving AI for fibre **[CXA108- Lipids- Week 4]** [Overview: Lipids] - Lipids (class of nutrients) are important sources of energy and include a number of compounds. - Triglycerides (Fatty acids and glycerol) - Phospholipids - Sterols - Fatty acids can vary in length, degree of unsaturation, number of double bonds. - Only small number lipids are important in human nutrition and as dietary energy sources. - Fatty acids and Triglycerides [Fatty Acids ] - All fatty acids have the same basic structure. - Chain of carbon and hydrogen atoms, with; - Acid groups (COOH) - Methyl group (CH~3~) - Long-chain fatty acids (LCFA) are found primarily in meat, fish and vegetable oils. - Medium- (MCFA) and short-chain fatty acids (SCFA) are found in dairy products. - The chemistry of a fatty acid, whether short or long, saturated or unsaturated and location of double bond -- influences the characteristics of foods and the health of the body. [Fatty Acids: Number of Double Bonds ] - Unsaturated fatty acids: lack hydrogen atoms and have at least one double bond. - The double bond is considered the point of unsaturation. - Monounsaturated fatty acids (MUFA): lack two hydrogen atoms and have one double bond. - Polyunsaturated fatty acids (PUFA): lack four or more hydrogen atoms and have at least two or more double bonds. - The omega number refers to the position of the first double bond. - Used in naming Omega-3 (n3) and Omega-6 (n6) fatty acids [Properties of Saturated Fat ] - Saturated fatty acids (SFAs) carry the maximum possible number of hydrogen atoms. - Saturated fats are solid at room temperature. - Saturated fat is more resistant to oxidation. [Properties of Unsaturated Fats ] - Unsaturated fatty acids have one or more points of unsaturation -- i.e. that may be; - Polyunsaturated fatty acids (PUFAs) - Monounsaturated fat acids (MUFAs) - Unsaturated fatty acids are generally liquid at room temperature - Polyunsaturated fat spoils most readily -- oxidative attack more prevalent with increasing number of double bonds. Monounsaturated fat is slightly less susceptible to spoilage. Name No. of Carbon atoms No. of double bonds Saturation Common food sources ---------------------- --------------------- --------------------- ----------------- --------------------------------------------- Stearic acid 18 0 Saturated Most animal fats Oleic Acid 18 1 Monounsaturated Olive, canola oils Linoleic Acid 18 2 Polyunsaturated Sunflower, safflower, corn and soybean oils Alpha-linolenic Acid 18 3 Polyunsaturated Soybean and canola oils, flaxseed, walnuts [Triacylglycerol (Triglycerides)] - Few fatty acids occur free in either foods or in the body - Triglycerides contain a glycerol to which 3 fatty acids are attached - Triglycerides are made through a series of condensation reactions - Most stored body fat is in form of triglycerides - Highly concentrated form of energy -- 37 kJ/g - Accounts \~95% dietary fat. [Characteristics of Solid Fats vs Oils ] Firmness: - Degree of saturation influences the firmness of fats at room temperature; e.g. butter is solid at room temperature. - PUFAs usually liquid vs SFAs usually solid. - Shorter carbon chain = softer fat at room temperature. [Comparison of Dietary Fats ] Stability: - Oxidation of fats produces a rancid taste and odour. - Polyunsaturated fats are most at risk of rancidity due to unstable double bonds. - PUFAs more readily oxidised as more unstable double bonds. - MUFAs less susceptible to oxidation. - SFAs most resistant to oxidation. - Manufacturers can protect fat-containing products against rancidity in three ways -- none of which are perfect. [Hydrogenation in Foods ] - Unsaturated fatty acids are saturated with hydrogen. 1. Protects against oxidation (rancidity) -- prolonging shelf life. 2. Alters texture (liquid vegetable oils more solid). - Manufacturers may add antioxidants to increase stability. - Most often, fat is partially hydrogenated -- creating a trans-fatty acid. [Trans-Fatty Acids ] - In nature most bonds are Cis- with dairy products and beef being the major dietary sources. - Change from cis to trans -- act like saturated fats in the body. - Trans-fats strongly increase cholesterol and risk of heart disease - Conjugated linoleic acid is a naturally occurring trans-fat that may be beneficial to health. [Phospholipids ] - Phospholipids have a unique chemical structure that allows them to have unique roles in the body - Phospholipids such as Lecithin used as a emulsifiers in food industry. - Food sources of lecithin include eggs, liver, soybeans, wheat germ and peanuts. - Phospholipids enable transport of lipids across cell membranes. [Sterols ] - Cholesterol is found in animal foods only -- meat, eggs, fish, poultry and dairy products (exogenous). - Plant-based sterols can interfere with cholesterol absorption. - Examples include Logicol and Flora Proactiv. - (1.6-3g/day) has been shown to lower total CHOL and LDL in both people with normal and high CHOL levels. - Cholesterol is a structural component of cell membranes and is a precursor for: - bile acids, sex hormones, adrenal hormones and vitamin D. - Liver produces 800--1500 mg cholesterol per day (endogenous). [Omega-3 and Omega-6 Fatty acids ] - The omega number indicates the position of the double bond closest to the methyl (CH3 ) end. [Essential Fatty Acids ] - Body can make all but two of the fatty acids. Linoleic acid (omega-6 family/n-6): - Make arachidonic acid, a conditionally essential fatty acid supplied by vegetable oils and meats. Linolenic acid (omega-3 family/n-3): - Can make small amounts of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). - important for the eyes, brain and heart. - Eicosanoids made from arachidonic acid and EPA are 'hormone like'; they include; - prostaglandins, thromboxanes and leukotrienes. [Omega-6 to Omega-3 Ratio ] - n-3 eicosanoids help lower blood pressure, prevent blood clot formation, protect against irregular heartbeats, and reduce inflammation. - n-6 eicosanoids tend to promote clot formation, inflammation, and blood vessel constriction. - Suggested n-6 to n-3 ratio around 4:1; typical ratio around 16:1 - Increasing amount of n-3s in diet is clearly beneficial, but reducing the amount of n-6s in diet to improve the ratio may not be helpful. - n-6s protect heart health by lowering LDL cholesterol and improving insulin resistance. [Essential Fatty Acids] [Transport of Lipids ] - Lipid transport is made possible by a group of vehicles known as lipoproteins. - These are lipid + protein complexes vary in lipid/protein content. 1. Chylomicrons -- largest of the lipoproteins. 2. VLDL (Very-Low-Density Lipoproteins) -- composed primarily of triglycerides. 3. LDL (low-density lipoproteins) -- composed primarily of cholesterol. 4. HDL (high-density lipoproteins) -- composed primarily of protein. [Lipoproteins] Triglyceride-Rich Lipoproteins (TRLs) - Chylomicrons - composed primarily of triglycerides. - made by the SI. - largest of the lipoproteins. - least dense. - get smaller as triglyceride portion is removed. - VLDL (Very-Low-Density Lipoproteins) - composed primarily of triglycerides. - made by the liver. - transport TAG to tissues. - get smaller and more dense as triglyceride portion is removed. Cholesterol-Rich Lipoproteins (CRLs) - LDL (Low-density lipoproteins) - composed primarily of cholesterol. - transport CHOL to tissues. - HDL (high-density lipoproteins) - composed primarily of protein - transport cholesterol from the cells to the liver. [Health Implications of Lipoproteins ] - High LDL: associated with higher risk of heart attack - High HDL: seems to have a protective effect - Factors that lower LDL and raise HDL: - Weight control. - Replacing saturated fat with unsaturated fat in the diet. - Soluble dietary fibre. - Phytochemicals. - Moderate alcohol consumption. - Physical activity. [Roles of Lipids in the body] - Primary roles of lipids are: - To provide energy, - Cushioning and - Insulation - The body can store unlimited amounts of fat when fat is consumed in excess - Adipose tissue - When body fat is markedly reduced or excessive, the type and quantity of adipokine secretions change, with consequences for the body's health. - The liver can also convert excess carbohydrate and protein to fat. [Overview: Lipid Metabolism ] - Lipids require little energy for metabolism. - Fat provides 60% of energy requirements for body at rest. - 1 kg adipose tissue (fat) provides 30,000 kJ. - WHY NOT 37,000 kJ when energy yield of 1 g fat = 37 kJ? - Require carbohydrate or protein for complete breakdown of fat. - Lipids provide minimal glucose for nerves and brain. - Fat breakdown in absence of carbohydrate creates ketone bodies. - Body cannot live on ketones alone -- disrupts acid-base balance. [Health Effects of Excessive Lipids ] - Excess fat in diet (Sat. fat), can lead to heart disease and obesity. - Cholesterol accumulates in the arteries, restricts blood flow and raises blood pressure. - Saturated fat raises LDL-cholesterol, increases risk of heart disease. - Food sources include high-fat cuts of beef and pork, and coconut, palm, palm-kernel oils. - Whole milk, cream, butter, cheese [Trans Fats and Cholesterol in the Diet ] - Trans-fatty acids in the diet increase LDL cholesterol and decrease HDL cholesterol. - Food sources include deep-fried foods using vegetable shortening, cakes, biscuits, doughnuts, pastry, crackers, snack chips, margarine, imitation cheese, and meat and dairy products. - Elevated LDL is a major risk factor for cardiovascular disease. - Weaker evidence for cancer, but some association with body fatness. - Dietary cholesterol has less effect on blood cholesterol than saturated fat/trans fat. - Food sources of cholesterol include egg yolks, milk products, meat, poultry and shellfish. - Dietary fat contributes significantly to weight gain and obesity. [Recommended Intakes of Lipids] - There are no set recommendations (RDI) for intake of dietary fats Australian Dietary Guidelines makes following recommendations: - Moderate total fat intake up to 30 per cent total energy intake. - Limit saturated fats. Proportion of energy in the diet from saturated and trans fats together: \< 8--10 per cent. On an average daily intake of 8,000 kJ: - AMDR 20-35% = 1,600--2,800 kJ from fat (45 to 75 grams daily). - \ - Eat more fish (two portions per week) and less meat. - Bake or grill the fish. - Functional foods are being developed. - Fresh, frozen or canned are all good sources. [Health Benefits of MUFAs/PUFAs] - Replacing saturated fat/trans-fat with monounsaturated / polyunsaturated fat most effective dietary strategy preventing heart disease. - Food sources of monounsaturated fat include olive, canola and peanut oil and avocados. - Food sources of polyunsaturated fat include vegetable oils (safflower, sesame, soy, corn and sunflower), nuts and seeds. - Emphasis on 'Mediterranean diet' pattern which features fresh, whole foods. Heart Disease: - Replacing saturated fats with unsaturated fats reduces LDL. Cancer: - Omega-3 from fatty fish may protect against some cancers -- by suppressing inflammation? Other Diseases: - Limited research suggests omega-3 from fish may protect against bone loss, asthma, periodontal disease and eye disease. - May play a role in improving memory and cognition -- not consistent with depression symptoms. [From Guidelines to Groceries ] - Lean and very lean options of meats should be chosen. - Choose fat-free and low-fat milks and milk products. - Choose a wide variety of vegetables, fruits, and wholegrain foods. - Avoid invisible fat from: - High-fat cheese, - Baked and fried foods, - fast foods, cakes, - Milk/white chocolate and - Biscuits. [Fat Options Among Protein Foods ] [Take Home Message on Fat Intake ] - Saturated fat and trans-fat are poor for heart health. - Cutting back on saturated fat will have no benefit, if saturated fat replaced with refined carbohydrates. - Example: white bread, white rice, mashed potatoes, sugary drinks. - Unsaturated fat in moderation (\ - Triglycerides (Fatty acids and glycerol) - Phospholipids - Sterols - Fatty acids can vary in length, degree of unsaturation, number of double bonds. - Only small number lipids are important in human nutrition and as dietary energy sources. - Fatty acids and Triglycerides [Fatty Acids ] - All fatty acids have the same basic structure. - Chain of carbon and hydrogen atoms, with; - Acid groups (COOH) - Methyl group (CH~3~) - Long-chain fatty acids (LCFA) are found primarily in meat, fish and vegetable oils. - Medium- (MCFA) and short-chain fatty acids (SCFA) are found in dairy products. - The chemistry of a fatty acid, whether short or long, saturated or unsaturated and location of double bond -- influences the characteristics of foods and the health of the body. [Fatty Acids: Number of Double Bonds ] - Unsaturated fatty acids: lack hydrogen atoms and have at least one double bond. - The double bond is considered the point of unsaturation. - Monounsaturated fatty acids (MUFA): lack two hydrogen atoms and have one double bond. - Polyunsaturated fatty acids (PUFA): lack four or more hydrogen atoms and have at least two or more double bonds. - The omega number refers to the position of the first double bond. - Used in naming Omega-3 (n3) and Omega-6 (n6) fatty acids [Properties of Saturated Fat ] - Saturated fatty acids (SFAs) carry the maximum possible number of hydrogen atoms. - Saturated fats are solid at room temperature. - Saturated fat is more resistant to oxidation. [Properties of Unsaturated Fats ] - Unsaturated fatty acids have one or more points of unsaturation -- i.e. that may be; - Polyunsaturated fatty acids (PUFAs) - Monounsaturated fat acids (MUFAs) - Unsaturated fatty acids are generally liquid at room temperature - Polyunsaturated fat spoils most readily -- oxidative attack more prevalent with increasing number of double bonds. Monounsaturated fat is slightly less susceptible to spoilage. Name No. of Carbon atoms No. of double bonds Saturation Common food sources ---------------------- --------------------- --------------------- ----------------- --------------------------------------------- Stearic acid 18 0 Saturated Most animal fats Oleic Acid 18 1 Monounsaturated Olive, canola oils Linoleic Acid 18 2 Polyunsaturated Sunflower, safflower, corn and soybean oils Alpha-linolenic Acid 18 3 Polyunsaturated Soybean and canola oils, flaxseed, walnuts [Triacylglycerol (Triglycerides)] - Few fatty acids occur free in either foods or in the body - Triglycerides contain a glycerol to which 3 fatty acids are attached - Triglycerides are made through a series of condensation reactions - Most stored body fat is in form of triglycerides - Highly concentrated form of energy -- 37 kJ/g - Accounts \~95% dietary fat. [Characteristics of Solid Fats vs Oils ] Firmness: - Degree of saturation influences the firmness of fats at room temperature; e.g. butter is solid at room temperature. - PUFAs usually liquid vs SFAs usually solid. - Shorter carbon chain = softer fat at room temperature. [Comparison of Dietary Fats ] Stability: - Oxidation of fats produces a rancid taste and odour. - Polyunsaturated fats are most at risk of rancidity due to unstable double bonds. - PUFAs more readily oxidised as more unstable double bonds. - MUFAs less susceptible to oxidation. - SFAs most resistant to oxidation. - Manufacturers can protect fat-containing products against rancidity in three ways -- none of which are perfect. [Hydrogenation in Foods ] - Unsaturated fatty acids are saturated with hydrogen. 3. Protects against oxidation (rancidity) -- prolonging shelf life. 4. Alters texture (liquid vegetable oils more solid). - Manufacturers may add antioxidants to increase stability. - Most often, fat is partially hydrogenated -- creating a trans-fatty acid. [Trans-Fatty Acids ] - In nature most bonds are Cis- with dairy products and beef being the major dietary sources. - Change from cis to trans -- act like saturated fats in the body. - Trans-fats strongly increase cholesterol and risk of heart disease - Conjugated linoleic acid is a naturally occurring trans-fat that may be beneficial to health. [Phospholipids ] - Phospholipids have a unique chemical structure that allows them to have unique roles in the body - Phospholipids such as Lecithin used as a emulsifiers in food industry. - Food sources of lecithin include eggs, liver, soybeans, wheat germ and peanuts. - Phospholipids enable transport of lipids across cell membranes. [Sterols ] - Cholesterol is found in animal foods only -- meat, eggs, fish, poultry and dairy products (exogenous). - Plant-based sterols can interfere with cholesterol absorption. - Examples include Logicol and Flora Proactiv. - (1.6-3g/day) has been shown to lower total CHOL and LDL in both people with normal and high CHOL levels. - Cholesterol is a structural component of cell membranes and is a precursor for: - bile acids, sex hormones, adrenal hormones and vitamin D. - Liver produces 800--1500 mg cholesterol per day (endogenous). [Omega-3 and Omega-6 Fatty acids ] - The omega number indicates the position of the double bond closest to the methyl (CH3 ) end. [Essential Fatty Acids ] - Body can make all but two of the fatty acids. Linoleic acid (omega-6 family/n-6): - Make arachidonic acid, a conditionally essential fatty acid supplied by vegetable oils and meats. Linolenic acid (omega-3 family/n-3): - Can make small amounts of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). - important for the eyes, brain and heart. - Eicosanoids made from arachidonic acid and EPA are 'hormone like'; they include; - prostaglandins, thromboxanes and leukotrienes. [Omega-6 to Omega-3 Ratio ] - n-3 eicosanoids help lower blood pressure, prevent blood clot formation, protect against irregular heartbeats, and reduce inflammation. - n-6 eicosanoids tend to promote clot formation, inflammation, and blood vessel constriction. - Suggested n-6 to n-3 ratio around 4:1; typical ratio around 16:1 - Increasing amount of n-3s in diet is clearly beneficial, but reducing the amount of n-6s in diet to improve the ratio may not be helpful. - n-6s protect heart health by lowering LDL cholesterol and improving insulin resistance. [Essential Fatty Acids] [Transport of Lipids ] - Lipid transport is made possible by a group of vehicles known as lipoproteins. - These are lipid + protein complexes vary in lipid/protein content. 5. Chylomicrons -- largest of the lipoproteins. 6. VLDL (Very-Low-Density Lipoproteins) -- composed primarily of triglycerides. 7. LDL (low-density lipoproteins) -- composed primarily of cholesterol. 8. HDL (high-density lipoproteins) -- composed primarily of protein. [Lipoproteins] Triglyceride-Rich Lipoproteins (TRLs) - Chylomicrons - composed primarily of triglycerides. - made by the SI. - largest of the lipoproteins. - least dense. - get smaller as triglyceride portion is removed. - VLDL (Very-Low-Density Lipoproteins) - composed primarily of triglycerides. - made by the liver. - transport TAG to tissues. - get smaller and more dense as triglyceride portion is removed. Cholesterol-Rich Lipoproteins (CRLs) - LDL (Low-density lipoproteins) - composed primarily of cholesterol. - transport CHOL to tissues. - HDL (high-density lipoproteins) - composed primarily of protein - transport cholesterol from the cells to the liver. [Health Implications of Lipoproteins ] - High LDL: associated with higher risk of heart attack - High HDL: seems to have a protective effect - Factors that lower LDL and raise HDL: - Weight control. - Replacing saturated fat with unsaturated fat in the diet. - Soluble dietary fibre. - Phytochemicals. - Moderate alcohol consumption. - Physical activity. [Roles of Lipids in the body] - Primary roles of lipids are: - To provide energy, - Cushioning and - Insulation - The body can store unlimited amounts of fat when fat is consumed in excess - Adipose tissue - When body fat is markedly reduced or excessive, the type and quantity of adipokine secretions change, with consequences for the body's health. - The liver can also convert excess carbohydrate and protein to fat. [Overview: Lipid Metabolism ] - Lipids require little energy for metabolism. - Fat provides 60% of energy requirements for body at rest. - 1 kg adipose tissue (fat) provides 30,000 kJ. - WHY NOT 37,000 kJ when energy yield of 1 g fat = 37 kJ? - Require carbohydrate or protein for complete breakdown of fat. - Lipids provide minimal glucose for nerves and brain. - Fat breakdown in absence of carbohydrate creates ketone bodies. - Body cannot live on ketones alone -- disrupts acid-base balance. [Health Effects of Excessive Lipids ] - Excess fat in diet (Sat. fat), can lead to heart disease and obesity. - Cholesterol accumulates in the arteries, restricts blood flow and raises blood pressure. - Saturated fat raises LDL-cholesterol, increases risk of heart disease. - Food sources include high-fat cuts of beef and pork, and coconut, palm, palm-kernel oils. - Whole milk, cream, butter, cheese [Trans Fats and Cholesterol in the Diet ] - Trans-fatty acids in the diet increase LDL cholesterol and decrease HDL cholesterol. - Food sources include deep-fried foods using vegetable shortening, cakes, biscuits, doughnuts, pastry, crackers, snack chips, margarine, imitation cheese, and meat and dairy products. - Elevated LDL is a major risk factor for cardiovascular disease. - Weaker evidence for cancer, but some association with body fatness. - Dietary cholesterol has less effect on blood cholesterol than saturated fat/trans fat. - Food sources of cholesterol include egg yolks, milk products, meat, poultry and shellfish. - Dietary fat contributes significantly to weight gain and obesity. [Recommended Intakes of Lipids] - There are no set recommendations (RDI) for intake of dietary fats Australian Dietary Guidelines makes following recommendations: - Moderate total fat intake up to 30 per cent total energy intake. - Limit saturated fats. Proportion of energy in the diet from saturated and trans fats together: \< 8--10 per cent. On an average daily intake of 8,000 kJ: - AMDR 20-35% = 1,600--2,800 kJ from fat (45 to 75 grams daily). - \ - Eat more fish (two portions per week) and less meat. - Bake or grill the fish. - Functional foods are being developed. - Fresh, frozen or canned are all good sources. [Health Benefits of MUFAs/PUFAs] - Replacing saturated fat/trans-fat with monounsaturated / polyunsaturated fat most effective dietary strategy preventing heart disease. - Food sources of monounsaturated fat include olive, canola and peanut oil and avocados. - Food sources of polyunsaturated fat include vegetable oils (safflower, sesame, soy, corn and sunflower), nuts and seeds. - Emphasis on 'Mediterranean diet' pattern which features fresh, whole foods. Heart Disease: - Replacing saturated fats with unsaturated fats reduces LDL. Cancer: - Omega-3 from fatty fish may protect against some cancers -- by suppressing inflammation? Other Diseases: - Limited research suggests omega-3 from fish may protect against bone loss, asthma, periodontal disease and eye disease. - May play a role in improving memory and cognition -- not consistent with depression symptoms. [From Guidelines to Groceries ] - Lean and very lean options of meats should be chosen. - Choose fat-free and low-fat milks and milk products. - Choose a wide variety of vegetables, fruits, and wholegrain foods. - Avoid invisible fat from: - High-fat cheese, - Baked and fried foods, - fast foods, cakes, - Milk/white chocolate and - Biscuits. [Fat Options Among Protein Foods ] [Take Home Message on Fat Intake ] - Saturated fat and trans-fat are poor for heart health. - Cutting back on saturated fat will have no benefit, if saturated fat replaced with refined carbohydrates. - Example: white bread, white rice, mashed potatoes, sugary drinks. - Unsaturated fat in moderation (\ - Essential proteins - Non-essential proteins - All proteins are essential nutritionally due to the amino acids -- used to synthesise proteins and variety of nitrogen-containing proteins that makes life possible. - Molecular architecture and activity of cells depends largely on proteins - Comprise over half of the solid content of cells. [Protein structure ] - Proteins are made from 20 different amino acids - Joined together by peptide bonds - Dipeptides, Tripeptides and Polypeptides - Amino acids sequence all different -- allows for a wide variety of possible proteins - Central Carbon - At least 1 amino group (NH~2~) and at least 1 carboxy (acid) group (COOH) - Side chain (R group) - Makes AA unique [Essential vs. Non-Essential Proteins ] - Non-essential amino acids (NEAA), also called dispensable amino acids, are ones the body can create from an amino group (--NH2 ) and metabolic intermediate. - Essential amino acids (EAA), also called indispensable amino acids, must be supplied by the foods people consume. - Conditionally essential amino acids refer to amino acids that are normally non-essential but if diet becomes deficient then they become essential under certain conditions. - Tyrosine \ - Measured by nitrogen balance - Protein denaturation is uncoiling of protein that changes its ability to function - Denatured by heat and acid - Synthesis determined by genetic information is unique to individuals. - Messenger RNA delivers sequencing code to nucleus of membrane. - Transfer RNA lines up amino acids and brings them to messenger RNA. [Sequencing Errors in proteins synthesis] - Sequencing errors can cause altered proteins to be made. - An example is sickle-cell anaemia, where an incorrect amino acid sequence interferes with the cell's ability to carry oxygen. [Role of Proteins in the body ] 1. Building materials for growth and maintenance - A matrix of collagen is filled with minerals to provide strength to bones and teeth. - Replaces tissues including the skin, hair, nails and GI tract lining. 2. Enzymes: - Facilitate anabolic (building up) - Catabolic (breaking down) chemical reactions. 3. Hormones: - Regulate body processes and some hormones are proteins. - Example: insulin. 4. Regulators of fluid balance - Plasma proteins attract water. - Maintain the volume of body fluids to prevent oedema which is excessive fluid. - Maintain the composition of body fluids. 5. Acid-base regulators: - Acts as buffers by keeping solutions acidic or alkaline 6. Transporters: - Carry lipids, vitamins, minerals and oxygen in the body. - Act as pumps in cell membranes, transferring compounds from one side of the cell membrane to the other. 7. Source of energy and glucose if needed: - Can provide some fuel and glucose -- Starvation and excess intake. 8. Antibodies: - Fight antigens, such as bacteria and viruses, that invade the body. - Provide immunity. - Other roles: - Blood clotting by producing fibrin which forms a solid clot. - Vision by creating light-sensitive pigments in the retina. [Overview: Protein Metabolism ] - Protein turnover creates 'free' amino acids. - Amino acid pool is made of free amino acids and those from dietary protein intake. - Can be used to make new proteins or nitrogen removed to be used as energy. - Protein and amino acids unique in the amount of N that they contain. - On average protein contains \~16% N. [Nitrogen Balance ] - One of the most common ways of assessing changes in body protein mass is the assessment of the difference between the intake and loss of N. - In healthy adult: 'Nitrogen balance'. protein degradation = protein synthesis, - Nitrogen balance = Nitrogen intake -- Nitrogen excretion -- When the body is in N equilibrium, N excretion is equal to N intake. - In childhood, pregnancy and recovery from illness likely to be in positive nitrogen balance. - Negative balance in illness, starvation, injury. [Deaminating Amino Acids] - Protein is deaminated to create non-essential amino acids or to make essential amino acids available. - By-products of deamination = ammonia (NH3 ) and keto acid (carbon skeletons). - Synthesis: amino acids can be used to make: - Neurotransmitters: adrenaline. - Precursors: vitamin niacin. - Energy and glucose: causes muscle wasting. - Fat: if excess protein consumed. [Converting Ammonia to Urea ] - Large amounts of protein intake will result in deamination to remove excess protein - Ammonia (NH~3~) is toxic to body - Is a base: upsets acid-base balance if amounts produced more than liver can handle - Liver combines NH3 with C02 = urea. - Production of urea increases as dietary protein increases. - Peaks at maximum rate with protein intakes approaching 250 g/day. [Excreting Urea ] - Urea is cleared from blood by kidneys. - Adequate fluids required to remove urea from blood. - Urea is main way of excreting unused nitrogen. - urea increases with increased protein intake. - Person who consumes high-protein diet (\100g/day) must drink plenty of water to dilute/excrete urea. - Risk for dehydration without increasing water intake. [Protein In Foods ] - Health is dictated by the Protein quality of a diet. - A high-quality diet supplies all the essential amino acids (EAA). - -- High-quality proteins provide all essential proteins needed to support the body's work -- low-quality proteins don't. - TWO important factors that influence protein quality. 1. Protein digestibility: -- Animal proteins are 90--99% absorbed. -- Plant proteins are 70--90% (Soy and legumes \~90%) absorbed. 2. Amino acid composition: - Limiting amino acids -- EAA supplied in less than amount needed to support protein synthesis. - -- Animal foods contain all EAA -- Complete proteins. - -- Plant foods tend to be missing one or more EAA -- Incomplete proteins. - Eating foods of high-quality protein is the best way to get all EAA. Complementary Proteins: - Combining plant foods that together contain all the EAA. - used by vegetarians. [Amino Acid Scoring for Protein Quality ] - Evaluates quality by determining AA composition with a reference protein -- commonly Egg Protein. Advantage: - Simple and inexpensive. - Easily identifies limiting AA. Weakness: - Fails to estimate the digestibility which can strongly affect quality. - Take a test protein and compare the amount of each amino acid to the amount found in 3210 units of essential amino acids in egg protein. - Leucine: 500 units (test) vs. 540 units (egg). - Lysine: 350 units (test) vs. 440 units (egg). - Leucine: 500/540 = 0.93. - Lysine: 350/440 = 0.80. - Lowest value AA is referred to as the 'limiting amino acid'. - If limiting amino acid is 80% of the amount in reference protein -- the test protein receives a score of 80. [Measure Protein Quality Using PDCAAS] - The PDCAAS or protein digestibility-corrected amino acid score compares AA composition of a protein with human AA requirements and corrects for digestibility. - First the protein's AA composition is determined, and then it is compared to the reference protein. - EXAMPLE: Pinto beans. - The amino acid score alone, however, does not account for digestibility. - Protein digestibility (rat studies), yields a value of 79 % for pinto beans. - PDCAAS = protein digestibility x amino acid score - PDCAAS for pinto beans = 0.79 x 0.84 = 0.66 [Health Effects of Protein ] - Protein deficiency and excesses can be harmful to health. - Protein deficiencies arise from protein-deficient diets and energy-deficient diets. - This is a worldwide malnutrition problem, especially for young children. - High-protein diets have been implicated in several chronic diseases. - Protein-energy malnutrition (PEM) can be chronic or acute. - Marasmus -- chronic PEM, - Kwashiorkor -- acute PEM, - or a combination of the two [Protein-energy malnutrition ] Marasmus (chronic PEM): - Greek "dying away" - Most common in infancy, 6 to 18 months. - Severe deprivation or impaired absorption of protein, energy, vitamins and minerals - Children in impoverished nations who don't have enough to eat and subsist of diluted cereal drinks that supply scant energy and low protein quality. - Usually develops slowly: - severe weight loss/muscle wasting, including the heart - \< 60% weight-for-age - anxiety and apathy - good appetite is possible - hair and skin problems. Kwashiorkor (acute PEM): - Ghanaian: describing birth position of a child. - Illness a child develops when the next child is born. - Older infants and young children, 18 months to 2 years of age. - Usually rapid onset from protein deficiency. - May be precipitated by other illness. - Inadequate protein intake increases susceptibility to infections. - some muscle wasting, some fat retention - growth is 60--80% weight-for-age - edema and fatty liver - apathy, misery, irritability and sadness - loss of appetite - hair and skin problems. [Health Effects of Protein ] - Heart Disease: - Foods high in animal protein also tend to be high in saturated fat. - Homocysteine levels increase cardiac risks. - Cancer: - A high intake of animal protein is associated with some cancers. - Adult bone loss (osteoporosis) - High protein intake associated with increased calcium excretion - Weight Control: - High-protein foods are often high-fat foods. - Protein at each meal provides satiety. - Adequate protein, moderate fat and sufficient carbohydrate better support weight loss. - Kidney Disease: - High protein intake increases the work of the kidneys. - A high intake does not seem to cause kidney disease. [Dietary protein Recommendations ] - AMDR of 15--25% energy intake from protein. - No Upper Level (UL) of intake has been currently set. - However, a UL of 25% protein as energy is recommended. Recommended Dietary Intake (RDI): - Men (19-70): 0.84 g/kg (\70): 1.07 g/kg - Women (19-70): 0.75 g/kg (\70): 0.94 g/kg - Assumptions for RDI: - people are healthy, - protein is mixed quality, - the body will use protein efficiently, [How Much Protein Should we Eat?] - Men: 19-50 = 3, 51-70 & 70+ = 2.5, - Women: 19-50 = 2.5, 51-70 & 70+ = 2 - Looking at the individual types of food consumed over a week, a maximum of 455 g of lean, cooked, red meat per week is recommended. [Recommended intakes of Proteins] - The protein requirements of athletes are slightly raised over the normal RDI - Use of protein for fuel (\ - A healthy diet should provide all protein requirements from a mix of animal and plant sources **[CXA108- Metabolism: Transformations, Interactions and Alcohol Metabolism -- Week 6]** [Overview: Metabolism] - Energy metabolism includes all the ways the body obtains and uses energy from food. - There are trillions of cells in the body -- all contribute to metabolism. - Liver cells are the most versatile and metabolically active. - Excessive alcohol (ethanol) intake interferes with multitude of chemical and hormonal reactions in the body [Chemical Reactions in the Body] - All energy originally comes from the sun - Photosynthesis in plants. - Humans and animals eat the plants and use the carbohydrate as fuel for their bodies - Energy-yielding nutrients are broken down to monosaccharides, fatty acids, glycerol and amino acids. - After absorption, enzymes and coenzymes can build more complex compounds. - In metabolism they are broken down further into energy (ATP), water and carbon dioxide. - Energy from catabolic reactions can be captured as ATP and used in other reactions. - The body converts the chemical energy of food to the chemical energy of ATP with about 50 per cent efficiency, radiating the rest as heat. - Coenzymes are required to facilitate reaction, for example B vitamins in metabolism of glucose [Metabolic Work of the Liver] [Anabolic vs. Catabolic Reactions ] - Building reactions: example condensation reaction = anabolic - Breakdown reactions: example hydrolysis = catabolic [Breaking down Nutrient for energy ] - Glucose. Glycerol. Fatty acids and amino acids are basic units derived from food - During catabolism body separates these atoms - Pyruvate (3-carbon) - Can make glucose - Acetyl-CoA (2-carbon) - Can't make glucose - All have a common pathway in the TCA cycle and the electron transport chain [Glucose to Pyruvate] - To provide energy nutrients are first converted to pyruvate - 'glycolysis'. - Pyruvate may be converted to lactic acid anaerobically (without oxygen) and acetyl CoA aerobically (with oxygen). - Aerobic pathways produce energy more slowly but can be sustained for longer and total energy yield is greater. - Eventually, all energy-yielding nutrients enter the TCA cycle and electron transport chain. [Pyruvate to Lactate] [Pyruvate to Acetyl CoA] - If O2 available and energy needed pyruvate enters mitochondria. - There a carbon group (COOH) from the 3- carbon pyruvate is removed to produce 2- carbon molecule that bonds with Coenzyme A -- Acetyl-CoA. - This step is metabolically irreversible. - Cells cannot retrieve the lost carbon atom to remake pyruvate [Glycerol and Fatty Acids for energy ] - The conversion of glycerol to pyruvate is easy because they are both three-carbon compounds. - Fatty acids-to-acetyl CoA reactions are called fatty acid oxidation. - Fatty acids cannot be used to synthesise glucose. - Glucose must be available to provide energy to the red blood cells, brain and nervous system [Summary: Nutrients for Energy] Nutrient Yields Energy Yields Glucose Yields Amino Acids and Body Proteins Yields Fat Stores --------------------- --------------- ----------------------------------------- ------------------------------------------------------------------------ ------------------- Carbohydrate Yes Yes Yes- when nitrogen is available, can yield non-essential amino acids Yes Lipids (Fatty acid) Yes No No Yes Lipids (Glycerol) Yes Yes -- when carbohydrate is unavailable Yes -- when nitrogen is available, can yield non-essential amino acids Yes Proteins Yes Yes -- when carbohydrate is unavailable Yes Yes [Final Steps of Catabolism ] - 4-carbon oxaloacetate has a critical role. - This TCA cycle will only continue if there is a constant supply of oxaloacetate. - Supplied from pyruvate i.e. carbohydrate [Fatty Acid vs. Glucose ] - Fat provides more energy as bonds in fat molecules are easily oxidised and result in more ATP. [Energy Balance ] - Healthy diet for the average person delivers between 8,000 and 10,000 kJ from foods -- active body uses most of them to do work - Maintaining body weight reflects that the body's energy budget is balanced. - Body weight changes little, if at all - When energy intake exceeds output, there is a gain in weight - An excess of any of the three energy-yielding nutrients contributes to increased body fat stores - Excess energy can come from protein, fat or carbohydrate [Feasting: Excess Energy] - When a person eats too much -- metabolism favours fat formation. - Excess protein: not stored, leads to increased protein oxidation and converted to fat, but this is inefficient and indirect. Its priority is other roles. - Excess carbohydrate is converted to fat, but this is inefficient and indirect. Its priority is glycogen stores. - Excess fat is efficiently converted to fat. - Excess energy from dietary fat → body fat uses \~5% of ingested energy intake. - Excess energy from dietary carbohydrate → body fat uses 25% of ingested energy intake. [Fasting: Inadequate Energy ] - CHO, FAT and PRO are all eventually used for energy -- fuel must be delivered to every cell. - Glucose is needed for the brain, nervous system and RBCs. - Glycogen in liver releases glucose and adipose tissue releases fatty acids to provide energy. - Once glycogen depleted -- body protein meets glucose needs. - As fasted state continues body uses fat to fuel the body -- shift to ketosis. - Ketones are produced when glucose is not available [Ketone Body Formation ] - Ketones normally in very small amounts in body - Formation will rise in fasting - Around day 10 of fasting it is meeting most of CNS energy needs - Ketosis causes a suppression of the appetite - Advantage so not to waste energy - Ketosis also slows metabolism to reduce energy output and try to conserve both fat and lean tissue [Symptoms of Starvation ] - Muscle wasting. - Decreased heart rate, respiratory rate, metabolic rate and body temperature. - Impaired vision. - Organ failure. - Decreased immunity. - Depression, anxiety and food-related dreams. [Alcohol Metabolism and Nutrition] - Alcohol (drinking) = ethyl alcohol, ethanol - The metabolism of alcohol is handled differently in the body - A standard drink (10g g pure ethanol) - Alcohol rich in energy (29 kJ/g) but is empty of nutrients - Alcohol interferes with metabolism and impairs health and nutrition. - There are potential health benefits to consuming moderate amounts of alcohol. - Alcohol behaves like a drug, therefore altering body functions [Australian Guidelines to Reduce the Health Risks from Drinking Alcohol] - Guideline 1: For healthy men and women, drinking no more than two standard drinks on any day reduces the lifetime risk of harm from alcohol-related diseases or injury. - Guideline 2: Drinking no more than four standard drinks on a single occasion. - Guideline 3: \ - Fibrosis is the second stage. - Cirrhosis is the most advanced stage of liver deterioration [Alcohol and Malnutrition] - Heavy drinkers may have inadequate food intake. - Impaired nutrient metabolism will result from chronic alcohol abuse. - Vitamin B6, folate and thiamine deficiencies are created by alcohol abuse. - Wernicke-Korsakoff syndrome is seen in chronic alcoholism. - Alcohol abuse can be fatal, abstinence during pregnancy recommended. [Take Home Message on Metabolism] - If energy intake exceeds the body's energy needs -- result will be weight gain regardless of whether the excess intake is from protein, carbohydrate or fat. - When fasting, the body makes a number of adaptations: - ↑ breakdown of fat to provide energy for most of the cells. - using glycerol and amino acids to make glucose for RBCs/CNS. - producing ketones to fuel the brain, suppressing the appetite, and slowing metabolism. - All of these measures conserve energy and minimise losses. - Excessive alcohol intake interferes with multitude of chemical and hormonal reactions in the body. - If alcohol is consumed it is important to remember moderation **[CXA108 - Energy Balance and Body composition -- Week 7]** [Overview: Energy Balance and Body Composition ] - Energy Balance usually equals Energy in + Energy Out -- although there are a number of factors influencing this making body weight regulation more complex - Health problems can be associated with both having too much and having too little body fat. Also being underweight and overweight - Because energy requirements vary from person to person, such factors as gender, age, weight and height, as well as the intensity and duration of physical activity, must be considered when estimating energy requirements. - To achieve and maintain a healthy weight -- be physically active and choose amounts of nutritious foods and drinks to meet your energy needs. [Energy Balance] - Ideally, energy intakes cover energy expenditure - Body weight stable: Energy Consumed = Energy expended - Energy Consumption \ Energy Expended = Weight Increase - Energy Consumption \< Energy Expended = Weight Decrease - Quick changes in body weight are not simple changes in fat stores. - Weight gained or lost rapidly includes some fat, large amounts of fluid and some lean tissues. - Excess energy stored as fat -- used for energy between meals - On kg body fat contains approximately 30,000 kJ energy - 1 kg body fat is approximately 87% fat (water and protein): - 870 g x 37 kJ/g = 32,190 kJ. - This '30,000 kJ rule' has been used for more than 50 years. - Has several limitations [Food Consumption ] - Composition of food/beverages determines energy they contain. - Measured using bomb calorimeter. - Direct calorimetry measures the heat energy released. - Indirect calorimetry measures the amount of oxygen consumed and carbon dioxide expelled. - Physiological fuel value is the difference between the number of kJs measured with calorimetry and the number of kJs that the human body derives from a food. [Food Intake: Appetite and Hunger] Appetite: - Prompts a person to eat -- or not to eat. Somehow the body decides how much and how often to eat -- when to start eating and when to stop. Hunger: - People eat for a variety of reasons, most obviously (although not necessarily most commonly) because they are hungry. - Most people recognise hunger as irritating feeling prompts thoughts of food and motivates them to start eating. - Hunger is physiological response to a need for food triggered by chemical messengers originating and acting in the brain, primarily in the hypothalamus. - Hunger influenced by presence/absence of nutrients in bloodstream, size/composition of preceding meal, customary eating patterns, climate, exercise, hormones and illnesses. - Hunger determines what to eat, when to eat and how much to eat. [Food Intake: Satiety and Satiation] Satiation: - During course of a meal, as food enters the GI tract and hunger diminishes, satiation develops. - Receptors in the stomach stretch and hormones such as cholecystokinin increase, - Person begins to feel full -- response is that satiation occurs, and person stops eating. Satiety: - After a meal, the feeling of satiety continues to suppress hunger and allows a person to not eat again for a while. - Whereas satiation tells us to 'stop eating', satiety reminds us to 'not start eating again' [Overriding Hunger and Satiety] - Eating triggered by signals other than hunger, even when body does not need food. - Some people experience food cravings when they are bored or anxious. May eat in response to any kind of stress -- negative or positive. - Repeatedly eating to relieve chronic stress can lead to overeating and weight gain. - Many people respond to: - External cues: time of day, or availability, sight and taste of food. - -- Environmental influences: large portion sizes, favourite foods, or an abundance or variety of foods stimulate eating and increase energy intake. - Overweight or obese people may be especially susceptible to external cues that trigger hunger and the desire to eat. - Eating can also be suppressed by signals other than satiety, even when a person is hungry. - People with the eating disorder anorexia nervosa, for example, use tremendous discipline to ignore the pangs of hunger. - Some people simply cannot eat during times of stress, negative or positive. [Sustaining Satiation] - Extent to which foods produce satiation and sustain satiety depends in part on the nutrient composition of a meal. - Protein-rich foods are considered the most satiating. - High fibre foods - Fat has the weakest effect on satiation during a meal. - High-fat foods are flavourful which stimulates appetite and can lead to passive over consumption. Also, energy dense -- deliver more kJ per bite. - Once in S.I. -- triggers CCK release which signals strong satiety/inhibits food intake. - Sustaining satiation strategies: - Larger salad starter - Wholegrain breads and cereals [How Fat Influences Portion Size ] - Portion size directly correlates with a foods satiety effect - Instead of eating a small portion of a high-fat food, person can feel satisfied by eating a larger portion of a high-protein/high-fibre food. [Message Central: Hypothalamus ] - Hypothalamus: control centre integrating messages about energy intake, expenditure, storage from brain, mouth, GI tract and liver. - Messages influence satiation -- some help control size of a meal; others help determine the frequency of meals. - Dozens of chemicals in the brain participate in appetite and energy balance. - Neuropeptide Y can cause food cravings (CHO), decrease energy expenditure and increase fat storage. - Amylin, Cholecystokinin (CCK), enterostatin, ghrelin - Glucagon-like peptide (GLP-1), pancreatic polypeptide (PP). [Energy Expenditure: BMR ] - Basal Metabolic Rate (BMR) is the rate the body expends energy to maintain essential body functions; e.g. breathing, making RBCs. - BMR rate may vary dramatically from person