Fundamentals of Nutrition PDF

NUTR *3210 FUNDAMENTALS OF NUTRITION Go to Course Syllabus  Essentials for the course Virtual Office Hours: Every Friday 10:00am-11:00am (on Zoom) Courselink Discussion Board – An excellent resource. Chances are at least one other person has the same questio...

NUTR *3210 FUNDAMENTALS OF NUTRITION Go to Course Syllabus  Essentials for the course Virtual Office Hours: Every Friday 10:00am-11:00am (on Zoom) Courselink Discussion Board – An excellent resource. Chances are at least one other person has the same question as you, so this is the most efficient way for all of us to communicate effectively. – When you make a post, please be sure that the title/subject of your post provides some detail as to the question. This helps to reduce repeat questions. All exam questions come directly from course lectures and additional information provided in class (i.e., fill in the blanks, Slido questions). Only reading the lecture slides will not be sufficient.  What is nutrition? The science of… food nutrients and substances in food their action, interaction and balance in relation to health and disease the processes by which the organism: – ingests, digests, absorbs, transports, utilizes, excretes food substances Source: AMA Council on Food and Nutrition, JAMA 242: 2335, 1979  Remember Nutrition is an integrative science  Looking back in time… 500 BC – Anaxagoras reasoned that food became the human body and must therefore contain ‘generative components’ (eluding to nutrients). 460 BC – Hippocrates recognized that medical examination should focus on the individual. 1614 AD – Santorio Sanctorius, considered to be the founding father of metabolic studies, determined that the sum total of visible excrement (urine, feces, sweat) was less than the amount of substance ingested. The first study that eluded to the concept of metabolism. 17th Century – Dietary supplementation can improve the health of individuals with particular diseases (e.g. iron fillings to wine could improve anaemic patients, citrus fruits prevents scurvy). The recognition that some nutrients are essential. 19th Century – Several scientist’s work led to the notion of vitamins and their importance in the prevention of diseases (Beriberi, rickets, etc). 20th Century – Nutrition, taking methods from a variety of different scientific fields (epidemiology, chemistry, biochemistry) moves beyond describing nutrients to asking ‘how much of each nutrient is needed for optimal health’. 21st Century – The term ‘nutritional genomics’ first appears in the literature, and describes the notion that diet and genes can interact to affect an individual’s health.  Nutrition Quotes “The doctor of the future will no longer treat the human frame with drugs, but rather will cure and prevent disease with nutrition.” – Thomas Edison (American Inventor) “Our food should be our medicine and our medicine should be our food.” – Hippocrates (Greek Physician) “To eat is a necessity, but to eat intelligently is an art.” – La Rochefoucauld (French Writer) “He that takes medicine and neglects diet wastes the skills of the physician.” – Chinese proverb “Those who think they have no time for healthy eating, will sooner or later have to find time for illness.” – Edward Stanley (English Statesman) “One should eat to live. Not live to eat.” – Socrates (Greek Philosopher) “Unfortunately, everything the experts tell us about diet is aimed at the whole population, and we are not all the same.” – The Scientist magazine  The Future of Nutrition Modern nutrition has moved from understanding how to prevent nutrient deficiencies to understanding the effects of over-nutrition. Now, the goal is to understand the optimal levels of nutrients required for health and well-being. However, people are not the same and respond differently to the same thing. Precision / Personalized nutrition.  Essential Nutrients? An essential nutrient is a chemical that is required for metabolism, but that cannot be synthesized or cannot be synthesized rapidly enough to meet the needs of an animal or human for one or more physiological functions. Nutrients are essential to the human diet if: 1. Removing the nutrient causes a deficiency and decline in health 2. Putting the nutrient back into the diet corrects the problem and health will return  Nutritional Deficiency Nutritional deficiencies occur when a person's nutrient intake consistently falls below the recommended requirement. Examples – Deficiency in Iron, Folate, and/or Vitamin B12: Anaemia – not enough red blood cells to transport oxygen around the body – important at key stages of development (e.g., pregnancy and infancy) – Thiamine (Vitamin B1): Beriberi – defective energy production – abnormalities in the nervous system – Vitamin C: Scurvy – Defective collagen production – Causes haemorrhaging, bleeding of the gums, etc. – Vitamin D: Rickets – Vitamin D is obtained from the diet and made by the body via UV radiation (sunlight) – defective bone growth MARCH 24, 2010 Understanding Nutrient Requirements Deficiency ≠ Nutritional Requirements – Deficiency  prevention of disease – Nutritional Requirement  ensure optimal health Why understand nutritional requirements? Prompted by World War 1 and food rations Limitations with first recommendations? Age, gender, body size, physical activity were not considered, but are important Nutrition research and statistics are used to establish nutrient requirements Understanding Nutrient Requirements Ever wonder where % Daily Values (DV) come from when you look at a food label? This is a simplified way for governments to provide consumers with information about the daily requirement for each nutrient. Daily Values are based on a 2,000 Calorie-a-day diet. Good tool, but recognize that these values provide a guide for the general population, but may need some tweaking for individuals based on their gender, age, etc. Daily Values are made using Dietary Reference Intakes (DRIs). DRIs are established by the National Academy of Sciences (private, non-profit organization made of US and Canadian scientists) using published data. Understanding Nutrient Requirements Dietary Reference Intake (DRI) is an umbrella term that refers to a set of reference values for nutrients - Estimated Average Requirement (EAR) - Recommended Dietary Allowance (RDA) - Adequate Intake (AI) - Tolerable Upper Limit (UL) DRIs were introduced in 1997 – DRIs for calcium and vitamin D were the last ones updated in 2011 RDAs for Units Males Females macronutrients Fat grams 44-78 g/day (20% - 35% of daily Calories) Carbohydrate grams 130 g/day 130 g/day Protein grams 56 g/day 46 g/day Based on a 2000 Calorie intake in adults aged 19-70 yrs Source: https://www.nal.usda.gov/fnic/dri-tables-and-application-reports  Establishing Nutrient Requirements Range of nutrient intakes required by individuals in a population subset (e.g., specific age group or gender) to achieve the same end point of growth, storage, or health. Establishing nutrient requirements: Estimated Average Requirement: EAR (the needs of 50% of population are met) Recommended Dietary Allowance: RDA (the needs of ~97% of population are met) EAR RDA RDA = EAR + 2*STDEV Normal distribution of x x population x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x [ Nutrient ] required to achieve the same endpoint of interest (e.g., growth, health, etc.)  Estimating Nutrient Requirements EAR and RDA values from a different perspective. - Tolerable Upper Limit (UL): The highest level of continuous daily nutrient intake that causes no risk of adverse effects. EAR UL RDA This gap varies for each nutrient Bookshelf ID: NBK208878 Deficit Excess [ Vitamin D] Rickets Osteomalacia Hypercalcemia  Estimating Nutrient Requirements What is an Adequate Intake (AI)? When sufficient scientific evidence is not available to establish an EAR and RDA, then an AI is proposed. An AI is based on much less scientific data. An AI is determined based on intake in healthy people who are assumed to have an adequate nutritional status (i.e., normal blood levels of a nutrient) The AI is expected to meet or exceed the needs of most individuals. EAR RDA UL AI Bookshelf ID: NBK208878  Studying Nutrition Cell culture models Animal models (rodents, pigs, etc.) Epidemiological cohort studies – Prospective vs. Retrospective Intervention studies – Randomized Control Trial (RCT) Challenges? Genetics, lifestyle, cultural habits, etc.  Nutrient Classes CARBOHYDRATES (& FIBRE) LIPID MACRONUTRIENTS ORGANIC PROTEIN (contain Carbon) VITAMINS MICRONUTRIENTS MINERALS INORGANIC WATER  “You are what you eat” How much body weight is Water 60% attributed to different nutrient classes? Vitamins & Minerals 2% Lipid 20-25% Protein 15% Carbohydrate 0.5% Source: Nutrition for Foodservice and Culinary Professionals, 7th ed  Metabolism Anabolism + Catabolism e.g. Insulin e.g. Glucagon (energy in) Cells (energy out) Tissues Nutrient Nutrient Building Building Blocks Blocks Recycled Nutrient Nutrients Waste for Intake Excretion  Water is an Essential Nutrient Intake by adult humans: 2.7L – 3.7L / day On average, 20% will come from foods Compare this to the average intake of: Carbohydrate: 250-350 g/d Fat: 60-80 g/d Protein: 50-80 g/d Functions: Solvent in biochemical reactions Catabolism (hydrolysis) Maintains vascular volume Nutrient transport Temperature regulation  Water Toxicity? Water intake >>> kidney’s ability to process (~0.9 L/h) BLOOD CELL H2O H2O Na2+ Na2+ Hyponatremia = water / sodium imbalance Source: https://ods.od.nih.gov/Health_Information/Dietary_Reference_Intakes.aspx Passcode: fose3s What characterizes hyponatremia? ⓘ Start presenting to display the poll results on this slide.  Hyponatremia Can occur from excessive fluid intake, under-replacement of sodium, or both. Typically avoided with urination. Causes central nervous system edema and muscle weakness. Source: https://ods.od.nih.gov/Health_Information/Dietary_Reference_Intakes.aspx Nutrition News FOOD / FEED COMPOSITION Proximate Analysis  Why look at food composition? Food analysis – the development, application and study of analytical methods for characterizing foods and their constituents. Why is this important? Information about foods, produce foods that are safe and nutritious, allow the consumer to make informed decisions – Quality Control Ensure food composition doesn’t change, characterize raw materials – Government Regulations Maintain quality of foods, ensure food industry makes safe foods with high quality, fair competition between companies, eliminate economic fraud Nutrition News  FEED SAMPLE (wet weight) Air dry 1. MOISTURE DRY MATTER Kjeldahl Boil in acid 2. ETHER Residue Filtrate 4. NITROGEN EXTRACT Boil in alkali Residue ASH + Crude Fibre Filtrate Ignite Ignite 3. ASH Ash 5. CRUDE FIBRE  1. Moisture (Water Content) FEED SAMPLE (wet weight) Air dry 1. MOISTURE DRY MATTER Why is determining water content in feed important? Water is weight and is part of the price of feed Water is weight and must shipped (more water = higher costs) Moisture content plays a role in storage conditions Too much and the food will spoil quickly Too little and the food will be less palatable Moisture dilutes energy and nutrients in food Moisture important for optimum intake and performance of animals  % moisture = wet weight – dry weight × 100% wet weight % dry matter = 100 - % moisture Potential sources of error / limitations: Drying can remove other volatile compounds, such as short chain fatty acids (SCFAs) and some minerals  This can cause a slight under-estimation of dry weight Differences between human and agricultural applications? Agricultural industry more interested in composition of dry matter Human food labelling is based on wet weight  2. Ether Extract (Crude Fat) FEED SAMPLE (wet weight) Air dry 1. MOISTURE DRY MATTER 2. ETHER EXTRACT  % crude fat = weight of ether extract ×100% wet weight of sample Potential sources of error / Gas chromatography (newer method) limitations: Other things are soluble in ether extract: – e.g., chlorophyll, resins, waxes in plants (which are not nutrients) – This will over-estimate crude fat determination Changes in current food labeling – Newer and more sensitive methods now exist  FEED SAMPLE (wet weight) Air dry 1. MOISTURE DRY MATTER 2. ETHER Why is it important to measure EXTRACT ASH content? Residue Nutritional labelling Quality and taste of food Microbiological stability Ignite Nutritional requirements Manufacturer processing 3. ASH  3. Ash (Mineral Content) % Ash = weight of ash × 100% wet weight of sample Potential sources of error / limitations: Volatile minerals may be lost when burning the residue No information about individual minerals ***It is now mandatory for food labels to indicate sodium content  FEED SAMPLE (wet weight) Air dry 1. MOISTURE DRY MATTER Kjeldahl 2. ETHER 4. NITROGEN EXTRACT Residue Two assumptions are made for the Kjeldahl analysis? Ignite 1. All nitrogen is in protein 2. All protein contains 16% nitrogen 3. ASH  4. Nitrogen (Crude Protein) 3 Main Steps to the Kjeldahl Analysis 1. Digestion – A food sample is mixed with sulfuric acid, which converts nitrogen into ammonia 2. Distillation – separates the ammonia 3. Titration – quantifies the amount of ammonia % crude protein = N in sample ×6.25 ×100% wet weight of sample Where do we get 6.25? Kjeldahl Analysis Assumption: ***ALL protein has 16% nitrogen*** 100% (total protein) ÷ 16% (nitrogen) = 6.25 Therefore:  (Nitrogen x 6.25) = Crude Protein  Kjeldahl Analysis Potential sources of error / limitations: 1. Assumes all proteins have 16% nitrogen – Actual range is 13-19% e.g., peanuts have ~18% nitrogen…therefore conversion factor = 5.5 e.g., milk has 15.7% nitrogen…therefore conversion factor = 6.38 2. Other sources of nitrogen – Any nitrates, nitrites, urea, nucleic acids, etc. in the food sample would therefore be part of the crude protein calculation *This would slightly over-estimate crude protein content Passcode: kgvooz You have a food product that has 20% nitrogen. What is the conversion factor to be used when calculating % crude protein? ⓘ Start presenting to display the poll results on this slide.  FEED SAMPLE (wet weight) Air dry 1. MOISTURE DRY MATTER Kjeldahl Boil in acid 2. ETHER Residue Filtrate 4. NITROGEN EXTRACT Boil in alkali Residue ASH + Crude Fibre Filtrate Ignite Ignite 3. ASH Ash 5. CRUDE FIBRE 5. Crude Fibre (Fibre)  Crude Fibre “Crude fibre” is not the same thing as “dietary fibre” “Crude fibre” is mainly cellulose and lignin (i.e., what remains after processing in the proximate analysis) The term “dietary fibre” is used to describe all fibre (both soluble and insoluble fibres) in a food. – To better estimate dietary fibre content, additional analyses are necessary Potential sources of error / limitations: Unable to distinguish different fibre components Measuring crude fibre under-estimates the actual dietary fibre content of feed by up to 50%. Why? – Dietary fibre includes cellulose, hemicellulose, pectin, mucilages, gums, lignin, etc. Soluble fibres are lost during the proximate analysis.  Dietary Fibre Non-digestible complex CHO Structural part of plants Insoluble Soluble Lignin Gums Cellulose Hemicellulose Pectins Mucilages Remains intact through intestinal Forms gel tract (does dissolve in water) (does not dissolve in water)  Nitrogen Free Extract (NFE) = Digestible Carbohydrate (CHO) Estimates starch & sugar content Potential sources of error / limitations: NFE accumulates ALL of the ERRORs that exist for the other components  General Comments about the Proximate Analysis Still used as the basis for human food labelling and animal feed analyses but… No information on ‘digestibility’ of food / feed – So we don’t know what will actually be absorbed by an organism. No information on specific amino acids, minerals, lipids, or carbohydrates. Has prompted the development of more advanced analytical assays to improve food characterization.  250g Pasture Grass or Salad Green 80% Moisture 50g Dry Matter (DM) 20% DM 16% of DM 8g 5% of DM 2.5 g 3.2% Crude Protein 1% Crude Fat 13.5 g 27% of DM 12% of DM 6g 5.4% Crude Fibre 2.4% Ash starting from wet weight, %NFE (Digestible CHO): 100% – (80%+3.2% + 2.4% + 5.4% + 1%) = 8.0% Digestible CHO in grams: 250 g (wet weight) x 0.08 = 20 g Passcode: kgvooz Your food sample weighs 135 g (wet weight). You determined that this food has 45% moisture, 6% crude fat, 2% ash, 9% crude protein and 8% crude fibre. Please calculate the weight (in grams) of the digestible carbohydrate in your food sample. ⓘ Start presenting to display the poll results on this slide. Passcode: kgvooz Your food sample weighs 250 g (wet weight) with 30% moisture, 8% crude fat, 6% ash, 4% crude fibre and 20% nitrogen-free extract. What is the weight of the nitrogen (in grams) in this food sample? Use the Kjeldahl Assumption (6.25 conversion factor). ⓘ Start presenting to display the poll results on this slide. THE DIGESTIVE SYSTEM  Lecture Overview Different species, different needs, different systems, but common themes 1. Simple system (w/o functional caecum) 2. Simple system (w/ functional caecum) 3. Ruminant system 4. Avian system  Gastrointestinal (GI) Tract Mouth Esophagus Stomach Small Intestine Large Intestine Caecum Rectum GI Tract = Digestive Tract ≠ Digestive System Digestive System refers to the GI Tract & associated organs (liver, pancreas, gallbladder)  General Terminology for Dietary Carbohydrates (CHO) & Digestion SOLUBILITY  Is CHO soluble in the aqueous environment of the digestive tract? – Yes = soluble; No = insoluble – (solubility not determined by enzymes) DIGESTIBILITY  Does the host organism have the enzymes necessary to digest CHO? – Digestible CHO versus non-digestible CHO (fibre) FERMENTABILITY  Do gut bacteria have the enzymes necessary to break down CHO? – Yes = fermentable; No = non-fermentable  1. Simple System w/o functional caecum e.g. human, pig, cat, dog Key features: Monogastric Non-functional caecum Suited for a nutrient dense, low fibre diet **Fun fact** Average human gut is ~16 feet long  How does digestion work? Oral cavity Food is chewed Food is mixed with saliva Two enzymes released: α-amylase and lingual lipase Stomach Empty = 50mL, Filled = 1-1.5L Gastric emptying = 2-6 hrs pH of stomach is acidic ~ 2 Food become “chyme” Gastric glands secrete gastric juice:  H2O, electrolytes, HCl, enzymes Pictures from A.D.A.M., Inc.  How does digestion work? Cont. Small intestine (duodenum, jejunum, ileum) Main site for nutrient digestion and absorption Surface area = 30m2 Intestinal motility controlled by longitudinal and circular muscles Chyme acidity neutralized by pancreatic juice Food digested by pancreatic juice and bile acids Large intestine (also called the colon) Site of fermentation Production of short chain fatty acids (SCFA), which are also known as volatile fatty acids (VFA) Site for water absorption Pictures from A.D.A.M., Inc.  Small Intestinal Surface Area 1. Kerckring folds 2. Villi (and Crypts) 3. Microvilli  Gut Bacteria 102 - 1012 bacteria / g content (region specific) – 500-1000 species identified per person in the gut Different species, but similar core functions – 1000:1 anaerobic to aerobic bacteria – Bacteria are very important for fermentation of non- digestible CHO. CHO fermentation produces many compounds, e.g., lactate and SCFA  2. Simple System w/ functional caecum e.g. horse, rabbit, hamster Foregut: stomach Hindgut: after the + small intestine small intestine Key Features ‘Pseudo-ruminant’ Hindgut fermenter Functional caecum All other regions of the gut function similar to the monogastric system Suited for a diet with large amounts of fodder and foraging **Fun Fact** Horse digestive tract ~100 feet  2. Simple System w/ functional caecum Purpose of a functional caecum? Enormous hindgut (20-30L capacity) filled with bacteria SCFA provide 70% of total energy needs for host Site for the production of vitamins Signs of an energy or nutrient deficiency? Coprophagy (eating feces) Young animals eating feces colonize their guts with bacteria  III. Multiple System: Ruminant e.g. cattle, sheep, goats Key Features: Large stomach divided into 4 regions 1. Reticulum 2. Rumen 3. Omasum 4. Abomasum System highly suited for animals that eat a high quantity of fodder and forage plant materials. All other regions of the gut function similar to the monogastric system Theory why there is a difference between cows and horses?  Ruminant Digestion Reticulum Honeycomb appearance in order to capture nutrients and trap foreign materials (wire, nails, etc) Rich in bacteria (fermentation vat) Rumen The largest section of the stomach Rich in bacteria (fermentation vat) Rumen papillae  increases surface area for absorption (like microvilli in the human intestine) Food is mixed & partially broken down, and stored temporarily papillae 60-80% of total energy produced here as SCFA  Ruminant Digestion Cont. Omasum Resorption of water and some electrolytes Filters large particles Abomasum Digestive enzymes secreted from gastric glands (HCl, mucin, pepsinogen, lipase, etc) The ‘true stomach’, similar to that of monogastric animals  Ruminant Digestion Cont. Fermentation takes place before entering the intestine (foregut digestion) Nutrients produced by bacteria then become available for digestion & absorption by the ruminant 1. Rumination 2. Eructation (belching)  Ruminant Digestion Cont. Rumen has 10-50 billion bacteria / g of ruminal fluid! Pros and Cons of a ruminant system? – Advantages Vitamin synthesis (e.g., B Vitamins, Vitamin K) Non-protein nitrogen used for making protein – Disadvantages Carbohydrates degraded into gases and lost through eructation Heat production  Digestibility Measure of the fraction of a specific nutrient (or of energy) that is extracted by the GI tract. Calculated from the amount of nutrient in the diet and the amount appearing in the feces. Represents a combination of nutrient release from the food matrix, microbial fermentation, and absorption. Why is this important? – Prevent deficiency and ensure essential nutrients are available to the organism.  1. Total Collection Method Allow the animal to adapt to the diet over a 7-21 day period Isolate animal for quantitative analyses Measure intake over a 3-10 day period Collect and weigh all feces Analyze for nutrient of interest Apparent Digestibility Total Intake – Total Feces = Coefficient Total Intake SOURCE: Khan et al, IJAB 2003 Example: What is the Apparent Digestibility of protein in this food sample? FRACTION INTAKE EXCRETION Dry matter (DM) 1000 g 100 g Protein (CP) 200 g 7g Fat (EE) 250 g 16 g CHO (NFE) 500 g 28 g Fibre (CF) 50 g 49 g Apparent Digestibility Total Intake – Total Feces = Coefficient Total Intake Protein = 200 g – 7 g = 0.965 200 g Protein = 96.5% Digestible  Limitations of the Total Collection Method Accuracy in measuring food intake Metabolic cages creates anxiety in animals, which may then behave abnormally Labour intensive Animals confined in costly equipment Not feasible for captive wild animals Metabolic cages  collect and analyze urine & feces  2. Indicator Method Also referred to as the “Marker Technique” Requires a marker: – Internal (a natural component of the feed) – External (a component added to the feed) Characteristics of a Marker? 1. Non-absorbable 2. Must not affect or be affected by the GIT 3. Must mix easily with the food 4. Easily & accurately measured in samples e.g., ferric oxide, chromic oxide  2. Indicator Method 1. Adapt animal to test diet (which contains a marker) 2. Collect a feed and fecal sample 3. Analyze each for marker and nutrient of interest relative to your indicator A–B Apparent Digestibility Coefficient = A Advantages of this method? Less labour intensive, ideal for wild animals  FRACTION INTAKE EXCRETION Dry matter (DM) 1000 g (100%) 100 g (100%) Protein (CP) 20% 7% Fat (EE) 25% 16% CHO (NFE) 50% 28% Fibre (CF) 4% 39% Chromic oxide (fecal marker) 1% 10% Indicator Method (the marker is used) A–B Apparent Digestibility Coefficient = A A = Ratio of Nutrient/Marker in Feed; B = Ratio of Nutrient/Marker in Feces 20% 7% - 1% 10% Protein = = 0.965 20% 1% Protein = 96.5% Digestible  Apparent versus True Digestibility Apparent digestibility under-estimates True digestibility The following are examples of things not considered when calculating Apparent digestibility: Endogenous secretions Epithelial cells E.g., fatty acids released from dying intestinal cells Bacterial growth in gut Nutrient synthesis E.g., biotin produced by gut bacteria Digestive enzymes Protein secretion E.g., digestive enzymes released by cells  True Digestibility 1. Perform digestibility study using a TEST DIET. 2. Switch to diet containing none of the nutrient of interest (ZERO NUTRIENT DIET). 3. Analyze feces after TEST DIET is cleared. 4. Subtract level of nutrient in feces of animals fed the ZERO NUTRIENT DIET from the TEST DIET.  True Digestibility A – (B – C) True Digestibility Coefficient = A A = Ratio of Nutrient/Marker in TEST DIET B = Ratio of Nutrient/Marker in Feces C = Ratio of Nutrient/Marker in Feces after ZERO NUTRIENT DIET  DIET 1 (TEST DIET) DIET 2 (ZERO NUTRIENT DIET) FRACTION INTAKE EXCRETION INTAKE EXCRETION Protein (CP) 20% 7% 0% 3% Fat (EE) 25% 16% 30% 15% CHO (NFE) 50% 28% 65% 35% Fibre (CF) 4% 39% 4% 39% Chromic oxide 1% 10% 1% 8% (fecal marker) A – (B – C) True Digestibility Coefficient = A 20% 7% 3% - - 1% 10% 8% Protein = = 0.984 20% 1% Protein = 98.4% Digestible Passcode: guvfmf You are interested in determining the true digestibility of protein using a test diet for your cows and switching to a diet that contains no protein (i.e., the zero nutrient diet). You obtained the following data. What is the true digestibility of protein? ⓘ Start presenting to display the poll results on this slide. ENERGY  Definitions Cellular source of energy = ATP – This cellular source of energy is supplied by the macronutrients in the diet – Sustains physical energy, anabolism, active transport, etc. What is the energy value of a food? – Calorie is a measure of heat to express the energy content of food Chemistry calorie ≠ Food Calorie 1000 Chemistry calories = 1 Food Calorie 1 Food Calorie = 1 kcal = 4.18 KJ (kilojoules) Energy required to raise the temperature of 1 kg (1L) of water by 1ºC  Estimating energy in foods Calorimetry = measurement of heat production Calorimetry uses heat as an indicator of the amount of energy stored in the chemical bonds of foods (carbon-hydrogen bonds) Bomb calorimeter – Works according to the principles of direct calorimetry (i.e., directly measures the amount of energy stored in chemical bonds of foods)  Bomb Calorimetry Dry and weigh sample (~1g), and place in enclosed chamber (the ‘bomb’) with oxygen Sample ignited Heat released is absorbed by water and measured Heat of combustion (gross energy) – Gross energy = maximum energy Potential Errors? – Overestimates energy We don’t digest food like a bomb calorimeter (e.g. fibre) – Doesn’t take into account the energy needed for digestion & absorption Why does fat provide more kcal per gram vs. CHO or protein? The heat of combustion describes the total energy released during a chemical reaction between a hydrocarbon and oxygen to release CO2 and H2O and heat. The chemical structure of CHO, fat, and protein influences the heat of combustion for macronutrients. CHO  ratio of hydrogen to oxygen = 2:1 Protein  has nitrogen, which affects gross energy measurement. However, in the body, nitrogen combines with hydrogen, and is eliminated as urea. This loss of hydrogen affects the heat of combustion. Fat  is less oxidized than CHO and protein  ratio of hydrogen to oxygen much greater than 2:1  has lots of hydrogen atoms available for cleavage and oxidation for energy  Physiological Fuel Values Heat of Energy Lost Apparent Physiological Combustion in Urine Digestibility Fuel Value (Gross Energy) (a) (b) (c) (a-b) x c units kcal/g kcal/g % kcal/g CHO 4.15 -- 97 4 Fat 9.40 -- 95 9 Protein 5.65 1.25 92 4 Physiological fuel values also called: Takes into account incomplete digestion Atwater Values Available energy Metabolizable energy  Fatty Acid Structure & Gross Energy Stearic acid C17H35COOH + 26 O2  18 CO2 + 18 H2O + 2712 kcal (Mol. Wt. = 284.5 g) Gross Energy (G.E.) = 2712 kcal/284.5 g = 9.53 kcal/g Metabolizable Energy (M.E.) = G.E. x 0.95 = 9.06 kcal/g Butyric acid C3H7COOH + 5 O2  4 CO2 + 4 H2O + 471 kcal (Mol. Wt. = 88 g) Gross Energy (G.E.) = 471 kcal/88 g = 5.35 kcal/g Metabolizable Energy (M.E.) = G.E. x 0.95 = 5.08 kcal/g Fatty Acid Structure & Gross Energy Stearic Acid Factors that affect – 18:0 heat of combustion of – 9.53 kcal/g fatty acids? Oleic Acid – Chain length – 18:1 Longer chain length – 9.48 kcal/g releases more energy – Degree of unsaturation Linoleic Acid The more double – 18:2 bonds, the less energy released (for equivalent – 9.42 kcal/g chain length fatty acids)  How can we use the Atwater Values? Fat 8 g × 9 kcal/g = 72 kcal Carbohydrate 22 g × 4 kcal/g = 88 kcal Protein 25 g × 4 kcal/g = 100 kcal Fibre?  Use of Metabolizable Energy Heat Increment of Feeding (HIF)  Also called the thermic effect of food  Energy used for the digestion, absorption, distribution & storage of nutrients  Comprises 5-30% of daily energy usage  Used to determine Net Energy  (Net Energy = Metabolizable Energy – HIF) Net Energy: supports basal metabolism, physical activity, growth, pregnancy, etc.  Total Energy Expenditure Three primary components to energy expenditure: 1. Basal metabolic rate (BMR) 2. Thermic Effect of Food (heat increment of feeding) 3. Physical Activity Energy Expenditure (PAEE) 4. (Thermoregulation)  Basal Metabolic Rate How is BMR measured? Shortly after waking up Post-absorptive state Lying down Completely relaxed Comfortable room temperature BMR = kcal per 24 hrs What tissues are most reflective of the BMR? Muscle and bone  Calculating BMR BMR = A×[M0.75] kcal/day Based on ‘metabolic weight’ – Metabolically active tissue (A) i.e., fat free mass (muscle and bone) Value for humans = 70; every species has its own value – Body weight (M)  in kilograms – 0.75 (Kleiber’s Law) – a constant used for all vertebrates, invertebrates and even unicellular organisms e.g., What is the BMR for a 65 kg person? BMR = (70)×[(65 kg)0.75] = 1602 kcal  Harris-Benedict Equation Determining your daily caloric needs sex weight height age BMR = 66 + (13.7 × W) + (5 × H) - (6.8 × Age) = Daily calories required BMR = 665 + (9.6 × W) + (1.8 × H) - (4.7 × Age) = Daily calories required physical activity Sedentary (little or no exercise): BMR × 1.2 Lightly active (light exercise/sports 1-3 days/week): BMR × 1.375 Moderately active (moderate exercise/sports 3-5 days/week): BMR × 1.55 Very active (hard exercise/sports 6-7 days a week): BMR × 1.725 Extra active (very hard exercise/sports & physical job): BMR × 1.9 Basal Metabolic Rate (BMR) vs. Resting Metabolic Rate (RMR). Same thing? http://www.bmi-calculator.net/bmr-calculator/harris-benedict-equation/  Factors that can affect BMR Genetics – Inheritance of a fast or slow metabolic rate Age – Young > old (because of greater muscle mass) Sex – Men > women (because of greater muscle mass) Exercise changes body tissue proportions Fat tissue (20% body weight, 5% metabolic activity) Muscle (30-40% body weight, 25% metabolic activity) Brain, liver, heart & kidneys (5% body weight, 60% metabolic activity)  but the size of these organs doesn’t change with exercise! Temperature (maintaining thermoregulation) Can you use body fat % to calculate BMR? If you can measure body fat %, you can have a more accurate measure of BMR. I indicated that the Harris-Benedict equation is commonly used to calculate BMR…which is not untrue…but there is another equation that can be used that takes into account fat % to calculate BMR. The Katch-Mcardle BMR equation – Same formula for men and women If a 70kg human finds out they have 20% body fat, this means they have 80% fat-free mass (FFM). 80% × 70 kg = 56 kg FFM BMR (using FFM) = 1579.6 kcal/d BMR (HB equation) = 1619 kcal/d Measuring Total Energy Expenditure All metabolic processes in the body generate heat Heat production can be used as a measure of energy expenditure Direct Calorimetry Indirect Calorimetry  Calorimetry GENERAL COMBUSTION EQUATION Combustion FUEL + O2 CO2 + H2O + HEAT DIET (CHO, Fat) Indirect Calorimetry Direct Calorimetry  Direct Calorimetry Measures the heat a person generates; total heat loss Very expensive! Impractical! USDA, Maryland, USA  Indirect Calorimetry Energy-releasing reactions in the body depend on the use of oxygen Indirect calorimetry estimates energy requirements by measuring: – Oxygen consumption (L) – Carbon dioxide production (L) – {Urinary nitrogen loss (g)} Note that this method can not account for anaerobic processes (i.e., production of lactic acid (lactate) from glucose during intense exercise)  Disadvantages: Hyperventilation, hard to get an airtight seal, masks are impractical Advantages: Useful with animals, can determine the type of substrate being oxidized  Respiratory Quotient (RQ) Provides information about: Energy expenditure Biological substrate being oxidized Ratio of metabolic gas exchange RQ = CO2 produced O2 consumed (Non-protein RQ  because protein contributes little to energy metabolism)  RQ varies for macronutrients Differences in chemical composition mean that each macronutrient requires a different amount of oxygen intake in relation to CO2 produced Carbohydrate: C6H12O6 + 6 O2  6 CO2 + 6 H2O + energy RQ = 6 CO2 / 6 O2 = 1 Fat: C16H32O2 + 23 O2  16 CO2 + 16 H2O + energy RQ = 16 CO2 / 23 O2 = 0.7  For each non-protein RQ value there is a caloric value for each L of O2 consumed or CO2 produced Table also tells you how much CHO and fat contribute to energy (This table will be given to you on exams) Passcode: 17lwq9 Under standard conditions, a person consumed 15.7 L O2/h and exhaled 12.0 L CO2/h. What is the energy expenditure per hour? ⓘ Start presenting to display the poll results on this slide.  Using RQ to determine energy expenditure… RQ = CO2 / O2  12.0L / 15.7L = 0.764 Kcal produced per L of O2 consumed or L of CO2 produced: (Use the RQ table) 4.751 kcal for 1 L O2 and 6.253 kcal for 1 L CO2  Using RQ to determine energy expenditure… From the previous table, caloric equivalent – 4.751 kcal for 1L O2 and 6.253 kcal for 1L CO2 Energy expenditure per hour:  15.7L O2 × 4.751 kcal/L = 74.6 kcal ~ 75 kcal/h  or… 12.0L CO2 × 6.253 kcal/L = 75 kcal/h If you want to determine the basal metabolic rate (BMR): – 75 kcal/h × 24 h = 1800 kcal per day Assumptions Made? 1. Only CHO and fat are metabolized. 2. No synthesis is taking place at the same time as breakdown. 3. Amount of CO2 exhaled = amount of CO2 produced by tissues CARBOHYDRATES  Unit Overview Classification & Structure Digestion & Function Metabolic Pathways …of carbohydrates  Carbohydrate Classification SIMPLE Monosaccharides Most common is glucose Naturally occuring Cannot be hydrolyzed into a smaller unit Considered a “reducing sugar” when the anomeric carbon is free Disaccharides Most common is sucrose Two monosaccharides joined by an acetyl bond (glycosidic bond) COMPLEX Oligosaccharides Polysaccharides Homo- & hetero-polysaccharides Glycogen (animal) Starch & Cellulose (plant) All CHO have a H:O ratio of 2:1  Monosaccharides TRIOSE METABOLITES OF GLUCOSE PENTOSE COMPONENTS OF DNA AND RNA HEXOSE NUTRITIONALLY THE MOST IMPORTANT Functional carbonyl group * * * * D-glucose D-fructose (an aldose) (a ketose) (an aldohexose) (a ketohexose) *Anomeric carbon (location of carbonyl group)  Stereoisomerism Why is this important? – Biological systems are stereospecific Same molecular formula and sequence, but differ in 3D space due to chiral carbon atoms – “L” and “D” isoforms What is a chiral carbon? – A carbon attached to four different atoms or groups Enantiomers (mirror image)  Stereoisomerism Fischer Projection Chiral carbon – Counting begins at the anomeric carbon for an aldose Exist in two forms: D vs. L Determined by the -OH group on the highest chiral carbon -OH on the right = D -OH on the left = L The number of stereoisomers for a molecule = 2n (where n = # chiral carbons) D-monosaccharides are nutritionally important because digestive enzymes are stereospecific for D sugars  Carbohydrate Nomenclature, cont. New chiral centre 2 possible conformations (α or β) β more common in nature GLUCOSE FRUCTOSE Fischer Projection Haworth Model Hemiacetal  made from an aldose Hemiketal  made from a ketose ***These reactions occur spontaneously (no enzymes involved) and are reversible  Haworth Model HEMIACETAL Converting a Fischer projection to Haworth Model OH What are the rules for what’s up and what’s down? OH 1) Non-acetyl/non-ketal CH2OH always points up 2) Hydroxyl (-OH) groups  if it’s right in the Fischer, it’s below in Haworth  if it’s left in the Fischer, it’s above in Haworth 3) Hemiacetal (α or β)  α has the -OH group pointing down  β has the -OH group pointing up  Haworth Model HEMIKETAL From Fischer projection to Haworth Model OH Rules for what’s up and what’s down? OH Same rules apply for hemiacetal and hemiketal sugars From biochemistry… LAB vs. RBA (left/above/beta vs. right/below/alpha)  Let’s review CHO Nomenclature Anomeric vs. chiral carbon – Anomeric carbon is the carbon with the carbonyl group – Chiral carbon has 4 different atoms / groups attached to it D vs. L configuration – D confirmation is nutritionally more important Alpha or beta configuration of hemiacetal or hemiketal group – More β than α configuration in nature – β has -OH group on anomeric carbon pointing up Fischer Projection vs. Haworth Model – Linear vs. cyclic  Let’s practice…. H C O H C OH H C OH H C OH CH2OH How many carbons? So this is called a what? Triose? Pentose? Hexose? PENTOSE Is this an aldose or ketose? ALDOSE So we could call this an aldopentose Passcode: cqzjie For the given diagram, A) which carbon is anomeric carbon; and B) which carbon is the highest numbered chiral carbon? ⓘ Start presenting to display the poll results on this slide. Passcode: cqzjie For the given diagram, how many stereoisomers exist? ⓘ Start presenting to display the poll results on this slide. Passcode: cqzjie For the given diagram, is this sugar in the D or L configuration? ⓘ Start presenting to display the poll results on this slide.  Disaccharides Most common oligosaccharide 2 monosaccharides attached by a glycosidic bond (formed between 2 hydroxyl groups) – For example, the -OH group at the anomeric carbon of one monosaccharide + the -OH group at carbon 4 or carbon 6 in the other hexose. Glycosidic bond can also be α or β Configuration of the -OH group on the anomeric carbon determines whether the disaccharide is α or β – possible outcomes [α(1,4), α(1,6), β(1,4), β(1,6)]  Common Disaccharides You don’t need to memorize these structures Found in sugar cane, fruits glucose + fructose Found in milk galactose + glucose Found in beer & liquor glucose + glucose  Polysaccharides Long strings or branches of monosaccharides (min. of 6) attached by glycosidic bonds Homopolysaccharides Heteropolysaccharides – Both exist in nature, but homopolysaccharides are more abundant in food  Polysaccharides Starch (Amylose, Amylopectin) is rich in plants – Both forms are polymers of D-glucose Glycogen is rich in animal tissue Is there an advantage for branching? – Yes. This provides a larger number of ends from which to cleave glucose when energy is needed.  Dietary Fibre Non-digestible complex CHO Structural part of plants Insoluble Soluble Cellulose Lignin Hemicellulose Pectins Gums Mucilages Remains intact through intestinal Forms gel tract (does dissolve in water) (does not dissolve in water)  Characteristics of Dietary Fibre Characteristics of solubility? – Water-holding ability Ability of a fibre to hold water, becoming a viscous solution – Adsorptive ability Ability of a fibre to bind enzymes and nutrients Insoluble (cellulose, lignin, some hemicelluloses) Remain intact throughout the digestive system Reduce transit time (i.e., things move quickly through the gut) Increases fecal bulk Soluble (pectins, gums, β-glucans, some hemicelluloses) Forms a gel Delays gastric emptying, increases transit time Slows down the rate of nutrient absorption  Health Benefits of Fibre Maintains function & health of the gut ↓ constipation (insoluble fibre) Stimulates muscle contraction to break down waste Decreases risk of bacterial infections ↑ satiety (soluble fibre) Delays gastric emptying Slows down nutrient uptake  Soluble Fibre and Disease Risk Decrease cardiovascular disease risk by lowering blood cholesterol ***Can also lower the risk of type II diabetes by binding some glucose in the digestive tract Psyllium seed husks Soluble fibre and cholesterol from foods reach the stomach and travel to the small intestine. Soluble fibre forms a gel which binds some cholesterol in the small intestine and carries it out of the body (i.e., in feces).  Classification & Structure Digestion & Function Metabolic Pathways …of carbohydrates  Carbohydrate Digestion Mouth – α-amylase (salivary) breaks down α-1,4-glycosidic bonds – Produces only a few monosaccharides – Cellulose and lactose are resistant, as are α-1,6-bonds – Stomach – α-amylase digestion continues until pH drops, then enzyme is inactivated – At this point, the pool of dietary CHO consists of small polysaccharides and maltose – Small Intestine – α-amylase (pancreas) – Active at a neutral pH – α-1,6 bonds are resistant and eventually produce isomaltose  Brush Border enzyme activity Also called sucrase sucrose  glucose + fructose Also called isomaltase isomaltose 2 glucose lactose  glucose + Maltose  2 glucose galactose See Diagrams Lactose Intolerance  Nutrient Transport Mechanisms Intestinal Lumen Enterocyte (cellular) cytoplasm Which transport mechanism used will depend on the nutrient’s: 1) Solubility 2) Concentration gradient 3) Molecular size  Monosaccharide absorption Enterocytes are polarized cells (in other words, they have an Very efficient “up” and a “down) Nearly all monosaccharides are taken up by enterocytes – What happens to the glucose then? Small amounts leak back out into the lumen from the enterocyte Small amounts diffuse into blood APICAL SGLT1 through the basolateral membrane Majority is transported into blood through GLUT2 Transport of glucose and galactose from BASOLATERAL lumen into blood is dependent on basolateral Na-K ATPase activity 3 Na+ 2K+ In contrast, fructose taken up by facilitated transport – GLUT5 on apical surface Glucose, galactose and fructose all SGLT1  sodium glucose transport 1 enter blood via basolateral GLUT2  Functions in the Body Glucose is the primary source of energy for cells – Glucose is the primary source of energy for tissues of the central nervous system (brain) and red blood cells Carbohydrates “spare” protein – Prevents breakdown of protein for energy – Allows protein to concentrate on building, repairing, and maintaining body tissue Carbohydrates prevent ketosis – When carbohydrates are limited, fats are broken down for energy. This leads to the production of ketone bodies, causing the body’s pH to become slightly acidic CARBOHYDRATES  Monosaccharide absorption Enterocytes are polarized cells (in other words, they have an Very efficient “up” and a “down) Nearly all monosaccharides are taken up by enterocytes – What happens to the glucose then? Small amounts leak back out into the lumen from the enterocyte Small amounts diffuse into blood APICAL SGLT1 through the basolateral membrane Majority is transported into blood through GLUT2 Transport of glucose and galactose from BASOLATERAL lumen into blood is dependent on basolateral Na-K ATPase activity 3 Na+ 2K+ In contrast, fructose taken up by facilitated transport – GLUT5 on apical surface Glucose, galactose and fructose all SGLT1  sodium glucose transport 1 enter blood via basolateral GLUT2  Functions in the Body Glucose is the primary source of energy for cells – Glucose is the primary source of energy for tissues of the central nervous system (brain) and red blood cells Carbohydrates “spare” protein – Prevents breakdown of protein for energy – Allows protein to concentrate on building, repairing, and maintaining body tissue Carbohydrates prevent ketosis – When carbohydrates are limited, fats are broken down for energy. This leads to the production of ketone bodies, causing the body’s pH to become slightly acidic  Classification & Structure Digestion & Function Metabolic Pathways …of carbohydrates  GLYCOGENOLYSIS GLUCONEOGENESIS GLYCOGENESIS CARBOHYDRATE METABOLISM GLYCOLYSIS KREB’S CYCLE HEXOSE MONOPHOSPHATE SHUNT  What to focus on… The purpose of each pathway Key steps and enzymes will be highlighted How the pathways are integrated in metabolism Conditions that make each pathway more or less active Nomenclature: +ve = activates; -ve = inhibits  GLUCOSE GLUCOSE-6-PHOSPHATE (G6P) 1 2 GLYCOGENESIS GLYCOLYSIS HEXOSE MONOPHOSPHATE SHUNT (PENTOSE PHOSPHATE PATHWAY) 3 Glucose has three fates in a cell: 1) Enters glycogenesis for energy storage 2) Enters glycolysis for energy production 3) Enters hexose monophosphate shunt to generate precursors for biogenesis How the cell uses glucose will depend on its requirements at the time. (i.e., ENERGY vs. BIOSYNTHESIS)  Glycogenesis Insulin Insulin +ve +ve Glycogen Synthase -ve Hexokinase (muscle) Glucokinase (liver) +ve Insulin  Glycogenesis, Cont. Glycogenin is an enzyme that serves as a scaffold on which to attach glucose molecules to build glycogen. – Think of this enzyme as a “primer”. It initially attaches glucose molecules to itself before glycogen synthase takes over and adds glucose to the growing glycogen store – 30,000+ glucose molecules can be contained in a single glycogen store  Glycogenolysis Glucagon +ve Glycogen Phosphorylase (breaks α-1,4- glycosidic bond) Glucose-6- phosphatase (liver only) GLYCOLYSIS GALACTOSE GLUCOSE 1 NADH ≈ 3 ATP Phosphofructokinase is the first committed step (irreversible) in FRUCTOSE Glucokinase / Hexokinase glycolysis Phosphofructokinase Fructose-1,6- bisphosphate -ve -ve ATP Glucagon 2 × Glyceraldehyde- (in the liver) 3 phosphate Red blood cells have no mitochondria Net Energy Yield from 1 Glucose 2 × Pyruvate In red blood cells, [2 NADH + 2 ATP (equivalent to ~8 ATP)] glycolysis is the only way these cells can Aerobic* Anaerobic* generate ATP *Metabolic fate of pyruvate depends on the cell’s Kreb’s Cycle Lactic Acid oxygen status  Anaerobic metabolism of glucose Lactic acid production – Occurs in muscle during prolonged exercise and in red blood cells – Pyruvate is converted into lactic acid in the cell’s cytosol – Regenerates NAD+, which allows glycolysis to continue – A net of 2 ATP is produced when glucose is converted to lactic acid Making ethanol – Doesn’t happen in the body – Yeast breaks down pyruvate into CO2 and ethanol – This is the basis of fermentation when you make wine and beer – Regenerates NAD+, which allows glucose to continue being broken down in glycolysis  Cori Cycle The Cori Cycle occurs in times where oxygen is unavailable (anaerobic state) in the muscle, leading to the production of lactate. Lactate is transported back to the liver, where gluconeogenesis allows for the conversion of pyruvate back to glucose. For 2 molecules of lactate to form glucose the cell consumes 6 ATP molecules. This is not sustainable because more energy is consumed than produced.  Hexose Monophosphate Shunt Important for NADPH production and ribose synthesis Occurs in the cytoplasm of a cell 6PGL 6PG G6P = glucose 6-phosphate; 6PGL = 6-phosphogluconolactone; 6PG = 6-phosphogluconate F6P = fructose 6-phosphate The Hexose Monophosphate Shunt is used to generate NADPH and precursors for nucleotide synthesis  Pyruvate Dehydrogenase: 1 NADH ≈ 3 ATP The “gatekeeper” to Krebs Cycle Pyruvate Dehydrogenase (PDH) Complex Several enzymes requiring several cofactors, 2× including 4 vitamins: 1) Thiamine, 2) Niacin, 3) Riboflavin, and 4) Pantothenic acid. Net Energy Yield (~6 ATP) 2 × [1 NADH / pyruvate]  Krebs Cycle (TCA or citric acid cycle) 1 NADH ≈ 3 ATP 1 FADH2 ≈ 2 ATP 1 GTP ≈ 1 ATP Pyruvate Pyruvate Carboxylase ATP ADP Takes place in mitochondrial matrix NAD+ NAD+ NAD+ GDP FAD Energy Yield from 1 Acetyl-CoA [3 NADH, 1 FADH2, 1 GTP (equivalent to ~12 ATP)]  How much energy do you get from 1 molecule of glucose? ATP yields from the complete oxidation of 1 molecule of glucose (1 NADH ≈ 3 ATP; 1 FADH2 ≈ 2 ATP; 1 GTP ≈ 1 ATP): Discrepancy in the literature about ATP yields from glucose: – In class we said: Glycolysis  net energy = 2 ATP + 2 NADH (~8 ATP) Pyruvate dehydrogenation  net energy = 1 NADH (~3 ATP) – X 2 because two pyruvates (total = 6 ATP) Kreb’s cycle  net energy = 3 NADH, 1 FADH2 & 1 GTP (~12 ATP) – X 2 because 2 acetyl CoA (total = 24 ATP) TOTAL ENERGY = 38 ATP THIS IS THE NUMBER WE WILL CONSIDER IN NUTR*3210! – However, some textbooks account for the fact that 2 ATPs are needed to import the 2 NADH produced from glycolysis into the mitochondria. THUS SOME BOOKS SAY TOTAL ENERGY = 38 ATP – 2 ATP = 36 ATP Passcode: gz8xbk How many NADH molecules are produced from the complete oxidation of 1 molecule of glucose? ⓘ Start presenting to display the poll results on this slide. Gluconeogenesis  Pathway that is active when glucose is needed by the body (e.g., during fasting)  Very active in liver, but can also happen in the kidney during starvation  Muscle & adipose tissue lack enzymes for gluconeogenesis  High physical activity produces muscle lactate, which travels to the liver in the Cori Cycle GLUCONEOGENESIS Glucokinase / Glucose-6- Hexokinase phosphatase Phosphofructokinase Fructose-1,6- bisphosphatase GLUCONEOGENESIS GLYCOLYSIS Enzymes to “bypass” irreversible steps and allow gluconeogenesis (enzymes expressed in liver, but not muscle or adipose) Pyruvate carboxylase Pyruvate kinase & Phosphoenolpyruvate (PEP) carboxykinase (PEPCK) In anaerobic states, muscle lactate returns to the liver for gluconeogenesis (Cori cycle)  Integrated Metabolism  Think beyond carbohydrates…  ‘Big picture’ of metabolic pathways:  inter-conversion and oxidation of fats, proteins, carbohydrates  Body’s energy needs and metabolic homeostasis Integrated Metabolism LIPIDS  Unit Overview Classification & Structure Digestion & Transport Metabolic Pathways …of lipids….  Lipids Soluble in organic solvents – e.g. ether, chloroform, acetone Wide variety of structures and functions – 10,000 different lipid species characterized Source of energy Major component of cell and organelle membranes  Lipid Functions 1. Concentrated source of energy  9 kcal/g 2. Palatability of foods & increase satiety 3. Source of essential fatty acids  α-linolenic acid (omega-3), linoleic acid (omega-6) 4. Source of fat-soluble vitamins  (A, D, E, and K) 5. Necessary for growth and development 6. Important precursors for the production of hormones 7. Affect inflammation and blood clotting 8. Key roles in disease development  Atherosclerosis, diabetes, obesity, etc...  Fatty Acids Saturated – Maximum # of H HYDROPHOBIC HYDROPHILIC atoms – Only single bonds Unsaturated – “Missing” H atoms – Double bonds Monounsaturated Monounsaturated fatty acid (Oleate) Polyunsaturated – cis or trans configuration Carboxylic acid group  FATTY ACIDS SATURATED MONOUNSATURATED POLYUNSATURATED (SFA) (MUFA) (PUFA) cis-9,12- Linoleic Acid Butyric Acid Oleic Acid (cis) cis-9,trans-11-CLA Palmitic Acid Elaidic Acid (trans) Arachidonic Acid  Fatty Acid Nomenclature Delta System (Δ) Omega System (ω) – Numbering starts from – Numbering starts from carboxyl end of fatty acid methyl end of fatty acid CH3-(CH2)5 18:2 Δ9,12 18:2 n-6 or 18:2 ω-6 Location of 1st # Carbons Double Bond # Double Bonds Position of Double Bonds # Carbons # Double Bonds Passcode: ypgulq Using the delta system for fatty acid nomenclature, which of the following notations describes the structure below? ⓘ Start presenting to display the poll results on this slide.  Essential Fatty Acids (EFA) Linoleic Acid (18:2 n-6) Alpha Linolenic Acid (18:3 n-3) Nuts, seeds, vegetable oils, etc Fatty fish, canola oil, almonds, etc Why are these fatty acids essential? Humans lack the enzymes necessary to insert double bonds beyond the delta-9 position of a fatty acid The delta-12 and delta-15 fatty acids are expressed in plants  Signs of Essential Fatty Acid Deficiency Are Whodeficiencies common? is susceptible NO. to a deficiency? Infants and hospitalized patients n-6 deficient n-3 deficient Skin dermatitis Ok Growth Ok Reproductive Ok maturity CNS Ok IQ development Retinal Ok Visual acuity development 2-3% of energy in diet 1% of energy in diet  EFA Desaturation and Elongation Eicosanoid Desaturation  insert double bond, remove 2 H Production Elongation  add 2 carbons (from malonyl CoA) (Pro-inflammatory) Linoleic Acid γ-Linolenic Acid Dihomo-γ-Linolenic Acid Arachidonic Acid (LA) (18:2 n-6) (GLA) (18:3 n-6) (DGLA) (20:3 n-6) (AA) (20:4 n-6) Desaturation Elongation Desaturation Delta-6 Desaturase Elongase 5 Delta-5 Desaturase α-Linolenic Acid Stearidonic Acid Eicosatetraenoic Acid Eicosapentaenoic Acid* (ALA) (18:3 n-3) (SDA) (18:4 n-3) (ETA) (20:4 n-3) (EPA) (20:5 n-3) Conversion Efficiency < 8% Eicosanoid Production (Anti-inflammatory) *EPA can be further converted into docosahexaenoic acid (DHA) Merino et al, Lipids in Health Dis, 2010 EFA Desaturation and Elongation Desaturation New double bond added at 6th position of carbon backbone from the carboxyl end Elongation Two carbons added (from malonyl CoA) at carboxyl end Desaturation New double bond added at 5th position of carbon backbone from the carboxyl end  Eicosanoids  Metabolites of 20-carbon fatty acids (primarily AA and EPA) PGD2 prostaglandins  Produced by most cells in the body  Hormone-like, function TXA2 locally thromboxanes  Role in inflammation, platelet aggregation, blood pressure, etc.  Implications for disease LTE4 leukotrienes  Triglycerides (TAG) Main dietary lipid and storage lipid Key in several pathways: Lipogenesis Lipolysis Transport in lipoproteins Structures Monoacylglycerol (MG, MAG) Diacylglycerol (DG, DAG) 3 Triglyceride / Triacylglycerol (TG, 2 TAG) 1 Fatty acid composition determines sn-1, sn-2, sn-3 positions physicochemical properties Ester bonds  Phospholipids (PL) Structural features More polar than TAGs Hydrophilic phosphate head group 1 2 Primary functions 3 Components of membranes Source of physiologically active fatty acids for eicosanoid synthesis Anchors membrane proteins Intracellular signaling  Sterols Steroid alcohols – Monohydroxy alcohols Structural features – Free or esterified with a fatty acid Cholesterol ester (CE) Sources of cholesterol: – Diet: meat & eggs (~40%) – Endogenous production (~60%) Primary functions – Essential components of membranes – Precursor for : Bile acid production Steroid sex hormone production Vitamin D synthesis  Classification & Structure Digestion & Transport Metabolic Pathways …of lipids….  Lipid Digestion Mouth – Lingual lipase – Continuously secreted Stomach – Gastric lipase – Continuously secreted – Lipases stable at low pH Liver Gallbladder – Storage of bile acids – Release of bile triggered by hormones Small Intestine – Pancreatic enzymes include pancreatic lipase, cholesterol esterase  Mixed Micelles  Digested lipids are emulsified by bile acids  Small, spherical complexes containing lipid digestion products plus bile acids (also called bile salts)  Can access the spaces between microvilli in the intestine  Originally thought that digested lipids were delivered into intestinal enterocyte cells by passive diffusion, but carrier- mediated transporters have now been identified  Bile acids are reabsorbed in our digestive tract BS = bile salt CL = cholesterol PL = phospholipid FA = fatty acid Source: Shi & Burns, Nat Rev Drug Disc 2004  Enterohepatic Circulation ***Soluble fibres Bile acids reduce the efficiency made in Cholesterol of enterohepatic liver circulation by holding Bile acids on to bile acids, ~95% bile which are then acids secreted in feces reabsorbed and recycled back to the liver Bile acids stored in gallbladder ~5% bile acids lost in feces Source: http://zavantag.com/docs/1632/index-2974.html?page=5 LIPIDS  Lipid Absorption Brush border enzymes: Pancreatic lipase Mixed Micelle Cholesterol esterase Phospholipase Lipoprotein  Lipid Transport Lipoprotein classification determined by: 1. Ratio of Lipid-to- Protein (which affects density) 2. Specific apolipoprotein (Apo) content (which affects receptor interactions) High Lipid High Lipid ‘BAD CHOLESTEROL’ ‘GOOD CHOLESTEROL’ Low Protein Low Protein Relative to VLDL, protein Low Lipid ApoB-48 ApoB-100 to lipid ratio increases High Protein ApoC, ApoE ApoC, ApoE ApoB-100, ApoC, ApoE ApoA family Source: www.medscape.com  Chylomicrons Chylomicrons increase in circulation after a meal Enter circulation at a slow rate Peaks between 30min-3hr after eating Since chylomicrons enter the lymphatic system before entering the blood, dietary lipids are available to adipose and muscle before arriving at the liver. Lipoprotein lipase (LPL) is located on the surface of endothelial cells lining small blood vessels and capillaries LPL not expressed in liver, but is expressed by adipose tissue and muscle LPL is activated by ApoC in chylomicrons LPL hydrolyzes the TAG in chylomicrons When chylomicrons become TAG-depleted, they are now referred to as a “chylomicron remnant” (CR) CR are removed from circulation through ApoE-mediated interactions with a receptor in the liver  Lipoproteins Cont. insulin ApoC + Chylomicron LPL ApoC Intestine ApoE CR ApoE (Dietary TAG) ApoB48 ApoB48 TAG hydrolyzed ApoC VLDL LPL ApoC Liver ApoE ApoE (Liver LDL TAG) ApoB100 ApoB100 HDL TAG hydrolyzed  Low-Density Lipoprotein (LDL) ApoC VLDL is the main ApoE VLDL transporter of ApoB100 newly synthesized TAG hepatic TAG either stored or LPL LDL taken up by the liver used for via LDL-receptors (i.e., receptor mediated energy endocytosis) *60% of blood cholesterol in LDL In a fasting subject ApoC  Brown & Goldstein ApoE Nobel Prize in Medicine in 1985 LDL ApoB100  High-Density Lipoprotein (HDL) ApoA  Cholesterol obtained from plasma membranes and then esterified directly Formation HDL on HDL of LCAT  Most blood cholesterol is esterified with fatty acids cholesterol esters Reverse Cholesterol Transport REVERSE CHOLESTEROL TRANSPORT  when HDL picks up cholesterol around the body and delivers it to the liver. Liver LCAT = lecithin-cholesterol acyltransferase (esterifies a fatty acid to cholesterol) SR-BI = scavenger receptor class B1 (HDL receptor in the liver) CETP = cholesterol ester transfer protein (transfers cholesterol ester from HDL to VLDL and/or LDL)  Fates of Cholesterol In the liver, cholesterol has several fates: 1. Converted into bile acids to replenish the bile acid pool 2. Secreted “as is” directly with bile, to be eliminated in feces 3. Packaged into VLDL and sent around the body LDL delivers cholesterol for essential functions but can also deposit cholesterol in unwanted places Higher HDL levels means more cholesterol returning to the liver  Dietary Cholesterol For healthy people, limiting Plant sterol Cholesterol dietary cholesterol does not change blood cholesterol much LUMEN But for those with high blood cholesterol, ↓dietary cholesterol will ↓ LDL Plant sterols compete with cholesterol for ABCG5 uptake by NPC1L1, but NPC1L1 plant sterols are then ABCG8 pumped back into the lumen by ABCG5 / G8 apical transporters. chylomicron NPC1L1: Niemann-Pick C1-Like 1 ABCG5: ATP-binding cassette sub-family G 5 LYMPH ABCG8: ATP-binding cassette sub-family G 8 chylomicron  Trans Fatty Acids Trans fats: Unsaturated fatty acids with at least one double bond in the trans configuration. There are both industrial and natural trans fats. Industrial trans fats produced during the hydrogenation of vegetable oils. – Companies do this to increase stability during cooking, longer shelf-life, and for palatability – Hydrogen atoms are added catalytically across double bonds Partial hydrogenation results in double bonds being converted from cis to trans Complete hydrogenation results in all double bonds becoming full saturated – ↑ the amount of hydrogenation, ↑ degree of saturation Industrial trans fats are completely banned in Canada as of 2018. Trans fats are also found naturally in ruminant fat – Milk fat contains 4-8% trans fat (best known is conjugated linoleic acid – CLA) – Natural trans fats are made in the rumen through bacterial fermentation. – Health affects linked with natural trans fats are equivocal.  Classification & Structure Digestion & Transport Metabolic Pathways …of lipids…. What happens in the Liver? What happens in Adipose Tissue?  Lipid metabolism in the liver following a meal Apolipoprotein CR Lipid metabolism in the adipose cell following a meal Triglyceride Pool Integrated Metabolism of Fat and CHO Where do lipids fit into the previously discussed metabolic pathways? GLUCONEOGENESIS? The glycerol backbone is glucogenic KREB’S CYCLE? Fat oxidation via acetyl CoA Lipolysis and Gluconeogenesis Lipases hydrolyze ester linkages (lipolysis) Triglyceride In adipose tissue – HSL (hormone sensitive lipase) -ve insulin – Cleaves a fatty acid from the HSL glycerol backbone The complete breakdown of a TAG molecule releases 1 glycerol and 3 fatty acids β-oxidation Glycerol can enter into glycolysis or gluconeogenesis (depends on cell needs) Fatty acids can undergo β- oxidation and used be to generate energy  β-oxidation and Kreb’s Cycle 1 NADH ≈ 3 ATP STEPS β α 1 FADH2 ≈ 2 ATP Kreb’s cycle  net energy = 3 NADH, 1 FADH2 & 1 GTP 1. Dehydrogenation FADH2 (~12 ATP) for 1 acetyl CoA 2. Hydration ETC 3. Oxidation NADH 4. Thiolysis *Each round of B-oxidation Acetyl CoA removes 2 carbons (acetyl CoA), and produces Kreb’s Cycle 1 NADH + 1 FADH2 Passcode: p424k2 How many times does a 10-carbon fatty acid go through beta-oxidation? ⓘ Start presenting to display the poll results on this slide. Passcode: p424k2 How many ATP equivalents are produced by the complete oxidation of this 10-carbon fatty acid? ⓘ Start presenting to display the poll results on this slide.  Example Question? How many times does a 10-carbon FA go through β-oxidation? Answer: 4 times (10C  8C  6C  4C  2 × acetyl CoA) Question? How many ATP equivalents are produced by the complete oxidation of this 10-carbon FA? 5 acetyl CoA + 4 NADH + 4 FADH2 (5 × 12 ATP) + (4 × 3 ATP) + (4 × 2 ATP) = 80 ATP equivalents Integrated Metabolism  Recommended Caloric Intake Food for thought…determining % of daily energy coming from macronutrients (caloric percentage) Men: 2500 kcal/day Women: 2000 kcal/day [g of Protein × 4 kcal/g] / 2500 kcal/day × 100% [g of Carbohydrate × 4 kcal/g] / 2500 kcal/day × 100% [g of Fat × 9 kcal/g] / 2500 kcal/day × 100% Dietitians of Canada recommend – Protein is 10-35% of daily calories (218g max) – Carbohydrate is 45-65% of daily calories (406g max) – Fat is 20-35% daily calories (97g max) (35% × 2500 kcal/d = 875 kcal/d energy from fat / 9kcal/g = 97g/d) Quadruple Bypass Burger (Arizona) ~ 8000 calories, 60g of fat in the meat patties alone!  BLT (Michigan) ~ 192g of fat in the bacon alone – 3 times more than the daily recommended amount  Garbage Plate (New York) Depending on what’s on the plate, fat content ranges from 93 – 203g of fat!  Ben & Jerry’s Vermonster (Vermont) Depending on the ice cream, fat content ranges from 120 – 400g! Mel’s Mega Burger (Texas) All included, over 5,000 kcal burger!!!! Midterm Exam Statistics Class average = 82.2% n = 297 Minimum = 36% Maximum = 100% 101 students received >90%. Among the above, 30 students received 100%. PROTEIN METABOLISM  Macronutrients so far… 1) CARBOHYDRATES (CHO) Health Canada recommended CHO intake: - Energy source 45-65% - No specific “essential” CHO per se - Includes Dietary Fibre - Dietary goal -  intake of non-digestible CHO Health Canada 2) LIPIDS (FAT) recommended fat intake: 25-35% - Rich source of energy - Two essential fatty acids: α-linolenic (ω-3) and linoleic (ω-6) - Key roles as precursors for signalling molecules, structural role in membranes, etc. - Goal is to  intake of total fat (especially saturated and trans fats), and  intake of MUFA and ω-3 fats  And now for the 3rd Macronutrient! 3) PROTEIN Health Canada recommended protein - Source of energy (if needed) intake: 10-30% - Substrate for Glucose Synthesis - Provides amino acids (AAs) for protein synthesis - Average consum