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Questions and Answers
What is the primary function of gastric juice in the stomach?
What is the primary function of gastric juice in the stomach?
How does bile contribute to fat digestion in the small intestine?
How does bile contribute to fat digestion in the small intestine?
What role does the pancreas play in digestion?
What role does the pancreas play in digestion?
Why is mucous secreted in the stomach?
Why is mucous secreted in the stomach?
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What does pancreatic juice contain that aids digestion?
What does pancreatic juice contain that aids digestion?
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What occurs during the final stage of digestion?
What occurs during the final stage of digestion?
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What happens to salivary enzymes in the stomach?
What happens to salivary enzymes in the stomach?
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What triggers the release of bile into the small intestine?
What triggers the release of bile into the small intestine?
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Which type of starch is resistant to digestion and can be found in raw potatoes?
Which type of starch is resistant to digestion and can be found in raw potatoes?
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What is a major result of the consumption of B-glucans from cereals like oats?
What is a major result of the consumption of B-glucans from cereals like oats?
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What must be taken with psyllium to prevent constipation or choking?
What must be taken with psyllium to prevent constipation or choking?
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What is the recommended daily intake of fibre for men aged 19 years and older?
What is the recommended daily intake of fibre for men aged 19 years and older?
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What happens to glycogen stores in the absence of dietary carbohydrates within approximately 18 hours?
What happens to glycogen stores in the absence of dietary carbohydrates within approximately 18 hours?
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What is gluconeogenesis?
What is gluconeogenesis?
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Which of the following is a benefit of consuming high-fibre foods?
Which of the following is a benefit of consuming high-fibre foods?
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What happens if a person suddenly increases their fibre intake?
What happens if a person suddenly increases their fibre intake?
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What percentage of the population retains efficient lactase activity into adulthood?
What percentage of the population retains efficient lactase activity into adulthood?
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What is the preferred energy source for brain and nerve cells?
What is the preferred energy source for brain and nerve cells?
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What is the recommended intake of whole grains per day based on Australian Dietary Guidelines?
What is the recommended intake of whole grains per day based on Australian Dietary Guidelines?
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What condition can result from undigested lactose in the gastrointestinal tract?
What condition can result from undigested lactose in the gastrointestinal tract?
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Which lipids are categorized as important sources of energy?
Which lipids are categorized as important sources of energy?
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What is a potential negative effect of excessive fibre intake?
What is a potential negative effect of excessive fibre intake?
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What percentage of energy intake is suggested for carbohydrates to support good health?
What percentage of energy intake is suggested for carbohydrates to support good health?
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What is the role of fatty acids in lipids?
What is the role of fatty acids in lipids?
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What happens to body weight when energy intake exceeds energy output?
What happens to body weight when energy intake exceeds energy output?
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Which nutrient is the least efficient in being converted to body fat when consumed in excess?
Which nutrient is the least efficient in being converted to body fat when consumed in excess?
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In a prolonged fast, after glycogen stores are depleted, which source of energy is primarily used next?
In a prolonged fast, after glycogen stores are depleted, which source of energy is primarily used next?
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What is a known effect of ketosis during fasting?
What is a known effect of ketosis during fasting?
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What is the energy content of alcohol?
What is the energy content of alcohol?
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Which of the following symptoms is NOT associated with starvation?
Which of the following symptoms is NOT associated with starvation?
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What role does glycogen play during energy deprivation?
What role does glycogen play during energy deprivation?
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What percentage of ingested energy from dietary fat is used to form body fat?
What percentage of ingested energy from dietary fat is used to form body fat?
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What type of fat is primarily responsible for raising LDL cholesterol levels?
What type of fat is primarily responsible for raising LDL cholesterol levels?
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Which of the following foods is a primary source of trans-fatty acids?
Which of the following foods is a primary source of trans-fatty acids?
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What percentage of total energy intake from saturated and trans fats should be limited according to dietary guidelines?
What percentage of total energy intake from saturated and trans fats should be limited according to dietary guidelines?
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Which dietary strategy is considered most effective in preventing heart disease?
Which dietary strategy is considered most effective in preventing heart disease?
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Which type of fat is NOT a major component of the Mediterranean diet?
Which type of fat is NOT a major component of the Mediterranean diet?
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Which food source is rich in monounsaturated fat?
Which food source is rich in monounsaturated fat?
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What is one potential health benefit of omega-3 fatty acids found in fatty fish?
What is one potential health benefit of omega-3 fatty acids found in fatty fish?
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What is the recommended intake for dietary fat as a percentage of total energy intake?
What is the recommended intake for dietary fat as a percentage of total energy intake?
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Study Notes
Digestion
- The small intestine is where carbohydrate, fat, and protein are digested due to secretions from various organs and glands.
- Salivary glands produce saliva in the mouth for easier swallowing and initial carbohydrate breakdown.
- The stomach produces gastric juice containing hydrochloric acid, enzymes, and mucus, which aids in protein digestion, kills bacteria, and protects the stomach lining.
- The pancreas releases pancreatic juice into the small intestine containing bicarbonate to neutralize acidic gastric juice and enzymes for all macronutrient digestion.
- The liver produces bile stored in the gallbladder, which emulsifies fat in the small intestine.
- Intestinal glands produce intestinal juice, containing enzymes for further breakdown of carbohydrates, fats, and proteins, along with mucus for intestinal wall protection.
Stomach and Gastric Juice
- Gastric glands secrete gastric juice, which is mainly composed of water, enzymes, and hydrochloric acid.
- The stomach's strong acidity contributes to protein digestion and eliminates ingested bacteria.
- The stomach lining is protected from its acidic environment by a mucus secretion.
- Gastroesophageal reflux disease (GERD) is a chronic digestive condition caused by gastric acid reflux into the esophagus.
Pancreatic Juice and Bile
- Pancreatic juice is released into the duodenum through pancreatic ducts.
- It contains enzymes for digesting all macronutrients and sodium bicarbonate, which neutralizes acidic chyme from the stomach.
- Bile, synthesized by the liver and stored in the gallbladder, is also released into the duodenum.
- The gallbladder releases bile into the small intestine in the presence of fat.
- Bile acts as an emulsifier, allowing fat to be suspended in water for enzyme action.
Final Stage of Digestion
- Energy-yielding nutrients are broken down for absorption in the small intestine.
- Vitamins, minerals, and water do not require digestion.
- Dietary fiber, such as bran and vegetables, does not form gels and is not easily digested by intestinal bacteria.
- Fiber promotes bowel movements and alleviates constipation.
- Resistant starches, found in legumes, raw potatoes, and unripe bananas, escape digestion.
- Phytic acid, associated with fiber, can bind some materials and affect mineral absorption.
Specific Fibre Products
- B-Glucans: found in cereal brans like oats and barley, potentially reduce cholesterol and postprandial glucose levels.
- Psyllium: used as a laxative in products like Metamucil, requiring adequate fluid intake to prevent constipation or choking.
Lactose Intolerance
- Lactase is required for lactose breakdown, with activity highest after birth.
- Only about 30% of adults maintain efficient lactase activity.
- Lactose intolerance is prevalent in populations of East Asian, West African, Arab, Jewish, Greek, and Italian descent, with about 90% affected.
- Northern Europeans have a lower prevalence, with about 5% lactose intolerant.
- Symptoms include bloating, abdominal discomfort, diarrhea, and gas production due to undigested lactose attracting water in the GI tract and providing food for bacteria.
- Causes include lactase deficiency with age, intestinal villi damage, medications, prolonged diarrhea, and malnutrition.
- Management options include gradually increasing milk product consumption, mixing dairy with other foods, spreading dairy intake throughout the day, and using acidophilus milk or yogurt.
Carbohydrate Metabolism
- Carbohydrates primarily provide glucose for energy, with most cells utilizing glucose as fuel.
- Glycogen is the storage form of carbohydrates in the body.
- The liver stores about ⅓ glycogen and releases it into the bloodstream when needed.
- Muscles store about ⅔ glycogen for their own use during exercise.
- Glycogen is stored with water, making it bulky and limiting storage capacity.
- In the absence of dietary carbohydrates, liver glycogen is depleted within about 18 hours.
- Fat stores provide a more significant energy reserve, lasting about two months.
- While glycogen is found in meats, it isn't a significant source of energy in the diet.
- Glucose is the preferred energy source for the brain, nerve cells, and red blood cells.
- Protein can be converted to glucose, but fat cannot.
- If glycogen stores are depleted, the body will utilize protein for glucose production.
- Gluconeogenesis is the process of converting a non-carbohydrate source into glucose.
Health Effects of Starch and Fibre
- A diet providing 45-65% energy from carbohydrates is considered optimal for health, according to the AMDR (Acceptable Macronutrient Distribution Range).
- Daily consumption of whole grains, vegetables, legumes, and fruits is recommended.
- High-fiber diets may offer protection against heart disease and stroke.
- Fiber intake helps reduce the risk of type 2 diabetes.
- It promotes intestinal health, hindering the absorption of unwanted substances.
- Fiber can protect against colon cancer by removing potential carcinogenic agents.
- High-fiber, whole-grain foods, low in fat and added sugars, aid in weight management and weight loss by delivering less energy.
Harmful Effects of Excessive Fibre Intake
- Individuals with limited stomach capacity, consuming a high-fiber diet, may not consume enough energy or nutrients to meet their needs.
- A sudden increase in fiber intake can cause transient abdominal discomfort, gas, and diarrhea.
- Gradual fiber intake increases allow the GI tract to adapt.
- Adequate fluid intake is essential to soften dietary fiber.
- Variety in fiber sources, including vegetables, fruits, legumes, and whole grains, is recommended.
- Excessive fiber intake can limit nutrient absorption by speeding up transit time and binding minerals.
- Mineral balance is generally not compromised when mineral intake is adequate, and fiber intake is within a reasonable range.
Recommended Intakes of Starch and Fibres
- Carbohydrates are an essential energy source, with no specific daily recommendation.
- The Australian Dietary Guidelines recommend consuming a generous amount of grains, mainly whole grains, aiming for approximately 6 servings daily.
- NRVs (Nutrient Reference Values) include an Adequate Intake (AI) for fiber:
- 30g/day for men (19 years and older)
- 25g/day for women (19 years and older)
- The Australian Guide to Healthy Eating recommends several servings of fruits, vegetables, and legumes daily to achieve the AI for fiber.
Overview: Lipids
- Lipids are a class of important nutrients, including triglycerides (fatty acids and glycerol), phospholipids, and sterols.
- Fatty acids vary in length, degree of unsaturation, and number of double bonds.
Trans Fats and Cholesterol in the Diet
- Trans-fatty acids in the diet raise LDL cholesterol and lower HDL cholesterol.
- Trans-fat sources include deep-fried foods, cakes, biscuits, doughnuts, pastries, crackers, snack chips, margarine, imitation cheese, and some meat and dairy products.
- Elevated LDL cholesterol is a significant risk factor for cardiovascular disease.
- While weak evidence exists for a link between trans-fats and cancer, an association with body fatness has been noted.
- Dietary cholesterol has less impact on blood cholesterol than saturated fat or trans fat.
- Sources of dietary cholesterol include egg yolks, milk products, meat, poultry, and shellfish.
- Dietary fat significantly contributes to weight gain and obesity.
Recommended Intakes of Lipids
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Specific recommendations for dietary fat intake (RDI) are not established.
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The Australian Dietary Guidelines recommend:
- Moderate total fat intake, up to 30% of total energy intake.
- Limiting saturated fats.
- Maintaining a combined proportion of saturated and trans fats in the diet at less than 8-10% of total energy intake. For an average daily intake of 8,000 kJ, the AMDR (20-35%) translates to 1,600-2,800 kJ from fat, equivalent to 45-75 grams daily.
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Including more fish (two portions weekly) and less meat in the diet is advised.
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Baking or grilling fish is recommended.
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Functional foods are being developed to provide additional health benefits.
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Fresh, frozen, or canned fish are suitable sources.
Health Benefits of MUFAs/PUFAs
- Replacing saturated and trans fats with monounsaturated and polyunsaturated fats is the most effective dietary strategy for preventing heart disease.
- Sources of monounsaturated fat include olive, canola, and peanut oils, as well as avocados.
- Food sources of polyunsaturated fat include vegetable oils like safflower, sesame, soy, corn, and sunflower, along with nuts and seeds.
- The Mediterranean diet pattern, emphasizing fresh, whole foods, benefits heart health.
Heart Disease
- Replacing saturated fats with unsaturated fats reduces LDL levels.
Cancer
- Omega-3 fatty acids from fish may protect against certain cancers by potentially suppressing inflammation.
Other Diseases
- Limited research suggests omega-3 fatty acids from fish may help prevent bone loss, asthma, periodontal disease, and eye disease.
- Omega-3 may improve memory and cognition, but its impact on depression symptoms is inconsistent.
Body Weight Changes
- Body weight changes minimally, if at all, when energy intake balances energy output.
- Excess energy intake, from any of the three energy-yielding nutrients, contributes to increased body fat stores.
Feasting: Excess Energy
- When a person consumes excessive calories, metabolism favors fat formation.
- Excess protein leads to increased protein oxidation and conversion to fat, but this process is inefficient and indirect due to protein's other essential roles.
- Excessive carbohydrate intake is converted to fat but is inefficient and secondary to glycogen storage.
- Excess fat is efficiently converted to body fat, representing a significant factor in weight gain.
- Excess energy from dietary fat results in only about 5% of ingested energy being stored as body fat.
- Excess energy from carbohydrates results in about 25% of ingested energy being stored as body fat.
Fasting: Inadequate Energy
- During fasting, the body utilizes carbohydrates (CHO), fat (FAT), and protein (PRO) as energy sources to fuel its cells.
- Glucose is essential for the brain, nervous system, and red blood cells (RBCs).
- Liver glycogen releases glucose, while adipose tissue releases fatty acids to provide energy.
- Once glycogen depletion occurs, the body breaks down protein to meet glucose needs.
- As fasting progresses, the body shifts to fat as its primary fuel source, entering a state of ketosis.
- Ketones are produced when glucose is unavailable.
Ketone Body Formation
- Ketones are present in the body in small amounts.
- Ketone production increases during fasting.
- By day 10 of fasting, ketones meet most of the central nervous system's energy needs.
- Ketosis suppresses appetite, reducing energy waste.
- Ketosis also slows metabolism, conserving both fat and lean tissue.
Symptoms of Starvation
- Muscle wasting
- Decreased heart rate, respiratory rate, metabolic rate, and body temperature
- Impaired vision
- Organ failure
- Weakened immunity
- Depression, anxiety, and food-related dreams
Alcohol Metabolism and Nutrition
- Alcohol (drinking) refers to ethyl alcohol or ethanol.
- Alcohol metabolism differs from other nutrients.
- One standard drink contains about 10 grams of pure ethanol.
- Alcohol is energy-rich (29 kJ/g) but devoid of nutrients.
- Alcohol consumption interferes with metabolism, negatively affecting health and nutrition.
- Moderate alcohol consumption may have some potential health benefits.
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