Lecture 4 - Energy


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Unformatted text preview: ENERGY METABOLISM ENERGY LINGO • Cellular source of energy = ATP • But this cellular source is supplied by nutrients in the diet (predominantly macronutrients) • So what is the energy value of a food? – Calorie (cal): measure of heat • kcal = 1000 calories = 1 Calorie = 1 Cal • 1 kcal = 4.18 KJ (kilojoules) • Energy required to raise the temperature of 1 kg (1L) of water by 1ºC ENERGY BALANCE ENERGY IN ENERGY OUT (FOOD & DRINK) (METABOLIC & CELLULAR FUNCTION) POSITIVE ENERGY BALANCE NEGATIVE ENERGY BALANCE •Weight gain / obesity •Infertility •Cardiovascular disease •Insulin resistance •Weight loss •Infection (*BMI ≥30, or about 30 lbs. overweight for 5’4” person) 1990 1999 2008 No Data <10% 10%–14% 15%–19% 20%–24% 25%–29% Source: CDC Behavioural Risk Factor Surveillance System ≥30% Historical perspective regarding Energy Metabolism • Antoine Lavoisier – Compared heat produced by a guinea pig with the production of CO2 – Ice calorimeter (heat produced equivalent to ice that melts) – CO2 formed from the reaction between oxygen and organic matter • Justin Liebig recognized that protein, CHO, and fats are oxidized • Max Rubner measured energy values of certain foods to determine caloric values Estimating the potential energy of foods • Calorimetry = measurement of heat production • Use heat as an indicator of the amount of energy stored in the chemical bonds of foods (carbon-hydrogen bonds) • Bomb calorimeter – Works on the principles of direct calorimetry Bomb Calorimetry • Dry and weigh sample (~ 1g), and place in enclosed chamber (the ‘bomb’) with oxygen • Sample ignited • Heat released in absorbed by water and measured • Heat of combustion (gross energy), i.e. max amount of energy • Potential Error? – Over-estimation - Over-estimation – We don’t digest fiber - We dont food like a bomb Fiber) – digest Doesn’t take intocalorimeter account(e.g. energy - Doesnt take into account energy used for digestion & absorption used for digestion & absorption Physiological Fuel Values Heat of Combustion (Gross Energy) Loss in Urine Apparent Digestibility Physiological Fuel Value (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 •Available energy •Metabolizable energy Takes into account incomplete digestion Atwater Values Why does fat provide more kcal per gram vs. CHO or protein? Does the chemical basis of CHO, fat, and protein have an effect? CHO --> ratio of hydrogen to oxygen = 2:1 ratio ofto hydrogen to oxygen 2:1 LipidCHO --> ratio of hydrogen oxygen much greater (i.e. less= oxidized) Lipid ratio of hydrogen to oxygen much greater (i.e. less oxidized) Protein --> has nitrogen, which contributes to gross energy. BUT…. our bodies don't use nitrogen for energy Protein has nitrogen, which contributes to gross energy. BUT…our bodies don’t use nitrogen for energy Sources of variation? CHO andand lipid --> structure CHO Lipid dependent structure dependent Protein --> relative nitrogen content of protein (think proximate analysis) Protein Relative nitrogen content of protein (think proximate analysis) Gross Energy vs. Available 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 yields 4 CO2 + 4 H2O + 471 kcal The Bomb Calorimeter measures ENERGY POTENTIAL of a compound (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 Factors affecting Gross Energy? • Stearic Acid – 18:0 – 9.53 kcal/g • Oleic Acid – 18:1 – 9.48 kcal/g • Linoleic Acid – 18:2 – 9.42 kcal/g • Factors that affect heat of combustion of fatty acids? Chain length - longer chain length means more energy – Chain length Degree of unsaturation - The more double bonds, the less energy (for equivalent chain length fatty acids) • Longer chain length means more energy – Degree of unsaturation • The more double bonds, the less energy (for equivalent chain length fatty acids) Fat 8 g fat * 9 kcal/g = 72 kcal Carbohydrate 22 g CHO * 4 kcal/g = 88 kcal Protein 25 g Protein * 4 kcal/g = 100 kcal Fibre? Use of Metabolizable Energy? Heat Increment of Feeding (HIF) Thermic effect of food Energy expended in digestion, absorption, distribution & storage of dietary nutrients 5-30% of energy expenditure Subtracted to yield Net Energy… Net Energy: supports basal metabolism, physical activity, growth, pregnancy, etc. Partitioning of Energy from Foods Gross Energy (GE) Fecal Energy - things that are not absorbed that are excreted Fecal Energy Digestible Energy (DE) Gases - Eg cow Gases Urinary energy Urinary Energy Metabolizable Energy (ME) Heat Increment of Feeding Heat increment of feeding Net Energy (NE) Basal Metabolic Activity Basal metabolic activity Total Energy Expenditure Three components to energy expenditure: 1. 2. 3. Basal metabolic rate (BMR) Thermic Effect of Food (TEF) also called HIF Physical Activity Energy Expenditure (PAEE) Basal Metabolic Rate • • • • • Shortly after waking Post-absorptive state Lying down Completely relaxed Comfortable room temperature BMR = kcal / 24hrs What tissues are most reflective of the BMR? Muscle and bone. How to calculate BMR BMR = A x [M 0.75] kcal/day • Based on ‘metabolic weight’ – Metabolically active tissue rather than body weight (A) • i.e. fat free mass (muscle and bone) • Human = 70, Dog = 30, Horse = 155 – Body weight (M) in kilograms – 0.75 (Kleiber’s Law) – used for all vertebrates, invertebrates and even unicellular organisms e.g. For a 70 kg person? BMR = (70) x [(70 kg) 0.75] = 1694 kcal Harris-Benedict equations for BMR (you do not need to memorize these equations) Determining your daily caloric needs ♂ BMR = 66 + (13.7 x W) + (5 x H) - (6.8 x Age) = Daily calories required weight height age ♀ BMR = 665 + (9.6 x W) + (1.8 x H) - (4.7 x Age) = Daily calories required Physical activity Sedentary (little or no exercise): BMR x 1.2 Lightly active (light exercise/sports 1-3 days/week): BMR x 1.375 Moderately active (moderate exercise/sports 3-5 days/week): BMR x 1.55 Very active (hard exercise/sports 6-7 days a week): BMR x 1.725 Extra active (very hard exercise/sports & physical job): BMR x 1.9 Factors that affect BMR • Genetics – Inheritance of a fast or slow BMR • Age – Young > old (because greater muscle mass) • Gender – Men > women (because 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 & kidney (5% body weight, 60% metabolic activity) • Temperatures (maintaining thermoregulation) Population based evidence…. Grey lines = men Black lines = women Almost 7400 adults Resting Energy Expenditure vs. Basal Metabolic Rate? Source: Lazar et al, Obesity, 2010 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 FUEL + O2 Respiration CO2 + H2O + HEAT DIET (CHO, Fat, & Protein) 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 utilization of oxygen • Estimates heat production by measuring: • Oxygen consumption (L) • Carbon dioxide production (L) • Urinary nitrogen loss (g) However, indirect calorimetry does not take into account anaerobic processes However….indirect calorimetry does not take into account anaerobic processes Direct vs. Indirect <1% difference very comparable Indirect Calorimetry in Research Respiratory Quotient (RQ) • Provides information about: - Energy expenditure - Biological substrate being oxidized • Energy expenditure • Biological substrate being oxidized • Ratio of metabolic gas exchange RQ = CO2 produced O2 consumed (Non-protein RQ) RQ varies for macronutrients • Differences in chemical composition mean that each macronutrient requires a different amount of oxygen uptake 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 Using RQ to determine energy expenditure… • Under standard conditions, a person consumed 15.7L O2 / h and expired 12.0L CO2 / h • RQ = CO2 / O2 12.0L/15.7L = 0.764 • From the previous table, caloric equivalent – 4.751 kcal for 1L O2 & 6.253 kcal for 1L CO2 • Calories produced per hour: – 15.7L x 4.751 kcal/L = 74.6 kcal ~ 75 kcal/h • Basal energy expenditure in the day – 75 kcal/h x 24h = 1800 kcal Assumptions made? 1- Only CHO, fat, and protein 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 The crossover concept Substrate utilization during exercise low intensity vs. high intensity Source: Berger, Top Clin Nutr 2004 ...
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