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Lecture

4. Energy Metabolism.doc

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Department
Animal Science
Course
ANSC 3120
Professor
c
Semester
Fall

Description
Energy Metabolism  Sum of all chemical reactions involved in obtaining and spending food energy o Eat to control energy intake o Heat is released by burning substrates; it can be measured  CO 2 Expended energy  H O 2  Energy = capacity to do work o The energy value of food means the amount of energy made available to a person’s body when the constituents of the food are metabolized following ingestion of the food o Units of measurement?  Calorie (cal) • Measure pf heat; energy value of food • kcal = 1000 calories = 1 Calorie o • calorie (small c): heat required to raise the temperature of 1 g of water 1 C • Cal or kcal = 1000 cal o Usual unit for human measurements  Joule (J) 7 • 10 X the energy required to accelerate a mass of 1 g by 1 cm/s • 1 kcal = 4.184 kJ • Don’t worry about J Energy Balance Energy Intake – Energy Expenditure Positive energy balance negative energy balance  Gaining total body energy • Growth • Pregnancy • Obesity? • Illness, fever • Dieting? Energy Metabolism 1 Energy Intake  Heat of combustion (diet sample) = GROSS ENERGY (GE) o Gross energy  Total possible energy in a food  Will over-estimate actual temp * utilization • Eg starch and fibre will have similar GE GE o Based on principle of ‘direct calorimetry’ o Amount of heat generated provides a direct measure of amount of energy stored in food’s chemical bonds o Measured using a ‘bomb calorimeter’ *  The sample is dried, weighed, Specific Heat ignited volume  Temperature increase of water * measured  GE of • Fat: ~9.4 kcal/g Weighed • Protein: ~5.65 kcal/g Dried Sample Propeller • CHO: ~ 4.15 kcal/g  Heat of Combustion: Chemical Basis o Why does fat provide more kcal per gram vs CHO or protein? o CHO and protein are already partially oxidized compared to fat Number of atoms/ C atom H O N a) CHO 2 1 - Eg glucose C 6 12 6 = 4.15 kcal b) Lipid 2 1/9 - Eg stearic acid C 18O36 2 = 9.34 kcal c) Protein 1.8 0.8 0.2 Eg glutamate C 5 9 N4 = 5.65 kcal Energy Metabolism 2 o Another example  CH 4 CH OH 2 CO 2  CH 4 methane  highly flammable  CH 2H – methanol  calmly flammable  CO 2 carbon dioxide  not flammable Physiological Fuel Values  Metabolizable Energy (ME) Values Experimentally Determined ME Heat of Apparent Loss in Urine Physiological Combustion Digestibility Fuel Value (GE) (a) (c) (b) (a-b) x c Units kcal/g % kcal/g kcal/g CHO 4.15 97 --* 4 Fat 9.40 95 -- 9 Protein 5.65 92 1.25 4 o ‘At water Fuel value’ Energy content of urea o GE and digestibility values represent weighted average in North American Diet  Could differ between individuals • Eg vegetarians might have decreased digestibility o Variations exist within each macronutrient class o * diabetics will have a glucose value  EG of how Gross Energy and Metabolizable differ within Macronutrient Classes 1. Stearic Acid C 17C35H + 26 O yiel2s 18 CO + 18 2 O + 2722 kcal Molecular Weight = 284.5 g Average for fats Gross Energy = 2712 kcal/284.5 g  9.53 kcal/g Metabolizable Energy = Gross Energy x 0.95  9.06 kcal/g digestibility 2. Butyric Acid – Butyrate  4C  VFA C 3 7OOH + 5O yie2ds 4CO + 4H 2 + 472 kcal Molecular Weight = 88 g Higher proportion Gross Energy = 471 kcal/88 g  5.35 kcal/g of oxidation Metabolizable Energy = Gross Energy x 0.95  5.08 kcal/g Lower due to greater level of inherent oxidation in the shorter fatty acid Average Energy Content of Nutrients Nutrient Cal/g kJ/g Protein 4 17 Fat 9 37 Carbohydrate* 4 17 Energy Metabolism 3 Alcohol 7 29 * The energy value for the total carbohydrate content may be less than 4 Cal/g if the carbohydrate includes sugar alcohols, polydextrose and/or dietary fibre Defined by manufacturer following some rules g X 9 energy loosely defined as ME Not digestible  8 g fat x 9 Cal/g = 72 Cal from fat o % of calories from fat o 1/3 of calories from fat  22 g carbohydrates x 4 Cal/g = 88 Cal from carbohydrates  25 g protein x 4 Cal/g = 100 Cal from protein o 72 Cal + 88 Cal + 100 Cal = 260 Cal overall o These values wouldn’t give proper values  Fibre? o To get these equal:  We left in fibre  But we multiply by 9/4/4 (ME values)  Rough estimates  Can remove fibre if you know it doesn’t provide energy
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