BPK 312 Nutrition for Fitness & Sport. Lecture 4 - Part 2. Measurement of Energy in Food & During Physical Activity

Transcription

1 BPK 312 Nutrition for Fitness & Sport Lecture 4 - Part 2 Measurement of Energy in Food & During Physical Activity 1. Heat of Combustion & Energy Value of Foods 2. Measurement of Human Energy Expenditure a. Direct Calorimetry b. Indirect Calorimetry 3. Respiratory Quotient (RQ), Weir Equation & Respiratory Exchange Ratio (RER) 4. Components of Energy Expenditure 1

2 1. Heat of Combustion & Energy Value of Foods Bomb Calorimeter Measures total energy value of foods Type of direct calorimetry Sealed chamber charged with oxygen Increase in water temperature directly reflects the heat released during a food s oxidation. Heat of combustion (HOC) Fig 6.1: A Bomb Calorimeter 2

3 1. Heat of Combustion & Energy Value of Foods Heat of Combustion (HOC) Heat of Combustion (HOC) = Gross Energy Value of Food From complete oxidation of macronutrients Determined in bomb calorimeter (Fig. 6.1) Ratio of H:O, CHO = 2:1, lipids >> 2:1 > # of H gives more energy from cleavage for oxidation HOC Energy Value of Macronutrients Mean = 4.2 kcal (e.g. glucose 3.74 kcal, glycogen 4.19, starch 4.20) Lipids Mean = 9.4 kcal (e.g. Beef or Pork fat 9.5 kcal, Butter fat 9.27, Veges & Fruit fat 9.30) Proteins Affected by (i) type of protein & (ii) N content of protein Nuts & seeds 18.9% N, whole milk 15.7% N etc Mean = 5.65 kcal (assumes 16 % N) 3

4 1. Heat of Combustion & Energy Value of Foods Net Energy Value = Actual energy available to the body Especially important for protein since N is not oxidized N combines with H to form urea NH 2 -CO-NH 2 chemical energy from protein; reduces HOC by 19% from 5.65 kcal/g to 4.6 kcal/g CHO & lipids HOC = net energy value 4

5 1. Heat of Combustion & Energy Value of Foods Net Physiological Energy of Macronutrients Coefficient of digestibility (COD) Gives final energy available to the body efficiency of digestion for each macronutrient COD = % of food energy digested & absorbed that is available for metabolic needs dietary fiber = digestibility e.g. Protein 1 92% (71.6%) x 5.65= 4.05 Lipid 95% x 9.4 = 8.93 CHO 97% x 4.15 = adjusted for energy loss in urine, this reduces the net energy available from 5.2 (i.e x 5.65) to 4.05 kcal/g 5

6 1. Heat of Combustion & Energy Value of Foods Atwater General Factors -rounded values to give net metabolizable energy for typical foods/meals Carbohydrates: 4 kcal/g Lipids: 9 kcal/g Proteins: 4 kcal/g EtOH*: 7 kcal/g e.g. Table 6.2: for 100 g Chocolate ice cream with chocolate chips *Ethanol (EtOH) 6

7 2. Measurement of Human Energy Expenditure a) Direct Calorimetry Directly measures energy expenditure Human calorimeter Airtight chamber A person lives or works in the chamber for an extended period of time. Changes in water temperature relate directly to an individual s energy metabolism. Direct Aerobic metabolism: Calorimetry Food + O 2 CO 2 + H 2 O + ATP + heat 7

8 2. Measurement of Human Energy Expenditure a) Direct Calorimetry Fig 6.3: Atwater-Rosa Whole Body human calorimeter 8

9 2. Measurement of Human Energy Expenditure b) Indirect Calorimetry Indirect calorimetry infers energy expenditure from measurements of oxygen uptake and carbon dioxide production using: Closed-circuit spirometry Open-circuit spirometry Portable spirometry Bag technique Computerized instrumentation Hood Aerobic metabolism: Indirect Calorimetry Food+ O 2 CO 2 + H 2 O + ATP + heat Doubly labeled water technique 9

10 2. Measurement of Human Energy Expenditure b) Indirect Calorimetry Closed- and Open-Circuit Spirometry Closed-circuit Subject breathes 100% oxygen from a prefilled container. A canister of soda lime absorbs the carbon dioxide in exhaled air. Open-circuit Subject inhales ambient air with 20.93% oxygen, 0.03% carbon dioxide, and 79.04% nitrogen. Indirectly reflects the ongoing process of energy metabolism 10

11 2. Measurement of Human Energy Expenditure b) Indirect Calorimetry Fig 6.4: Closed circuit Spirometry filled with 100% oxygen 11

12 2. Measurement of Human Energy Expenditure b) Indirect Calorimetry Portable Spirometry & Bag Technique Portable spirometry Ambient air passes through a twoway valve. Expired air travels through a gas meter that measures total expired air. Bag technique Ambient air is breathed through one side of a valve. Air is expelled through the other side of the valve. Fig 6.5: 12

13 2. Measurement of Human Energy Expenditure b) Indirect Calorimetry Computerized Instrumentation Computer interfaces with A flow-measuring device that records air volume breathed O 2 & CO 2 analyzers that measure the composition of the expired gas mixture Mouth piece/nose clip or hood Fig 6.4: Fig 6.7: Ventilated hood, Open circuit spirometry Fig 6.6: Computerized instrumentation for indirect calorimetry 13

14 2. Measurement of Human Energy Expenditure b) Indirect Calorimetry Doubly Labeled Water Technique A good way to assess total EE over prolonged periods ingest water, equilibrate, initial sample, 7-14 d later final sample predicts Co2 production to within 3-8% H 18 O 3 H (Doubly-labeled water) 3 H lost as body H 2 O in urine, sweat, & w/ breathing 18 O is lost as H 2 O & CO 2 Use an est. RQ=VCO 2 /VO 2 =0.85 & known/measured CO 2 prod. rate e.g. RQ =0.85 & VCO2 = ~0.2 L/min Initial sample VCO 2 = 288 L/day x 6 days = 1728 L/6 days VO 2 =VCO 2 /RQ = 1728 L over 6 days/0.85 =2033 L VO 2 over 6 days With RQ = 0.85 & ~5 kcal expended/ L O 2 EE = 2033 L x 5 kcal/l = 10,165 kcal expended over 6 days isotope in body Rate of loss of 18 O > 3 H time Final sample 3 H 18 O 14

15 2. Measurement of Human Energy Expenditure b) Indirect Calorimetry Doubly Labeled Water Technique Advantages: use with volunteers outside lab to give free-living rate of energy expenditure (EE), much EE higher rates than in lab no equipment attached to the volunteers easy to sample of body fluids, saliva, urine or blood Disadvantages measures CO 2 production, estimates VO2 Expensive for isotopes and lab set up with isotope ratio mass spectrometers etc H 18 O 3 H (Doubly-labeled water) 15

16 3. The Respiratory Quotient (RQ), Weir Equation & Respiratory Exchange Ratio (RER) The ratio of carbon dioxide produced to oxygen consumed RQ = CO 2 produced O 2 consumed The RQ provides information about the nutrient mixture catabolized for energy. The RQ equals 1.00 for carbohydrate, 0.70 for fat, and 0.82 for protein. 16

17 3. The Respiratory Quotient (RQ), Weir Equation & Respiratory Exchange Ratio (RER) Weir Equation calculation of caloric expenditure from ventilation (V E ) & % O 2EXPIRED EE (kcal/min) = V E X [1.044 ( X % O 2EXPIRED )] Value in square brackets [ ] = Weir Factor, - e.g. V E = 50 L/min, O 2EXPIRED =16% - EE (kcal/min) = 50 x [ x 16] = 12.3 kcal/min Weir Eqn: assumes constant energy transfer from protein of 12.5% 17

18 3. The Respiratory Quotient (RQ), Weir Equation & Respiratory Exchange Ratio (RER) The Respiratory Exchange Ratio Ratio of carbon dioxide produced to oxygen consumed Computes in exactly the same manner as RQ R > 1.00 Overbreathing Exhaustive exercise R < 0.70 After exhaustive exercise with glycogen depletion 18

19 3. The Respiratory Quotient (RQ), Weir Equation & Respiratory Exchange Ratio (RER) Non Protein RQ varies with % oxidation of CHO/Fat For most purposes RQ is assumed to be from 40% CHO & 60% fat Gives caloric equivalent of kcal/ L O 2 ; max error for estimate is ~3-5% e.g. Exercise for 30 min VO 2 = 3.22 L/min VCO 2 = 2.78 L/min RQ = 2.78/3.22 = 0.86 EE = 3.22 L O 2 /min x kcal/l O 2 = kcal/min x 30 min = total of 471 kcal expended 19

20 4. Components of Energy Expenditure Energy Expenditure During Rest & Physical Activity Three factors determine total daily energy expenditure: Resting metabolic rate Thermogenic influence of food consumed Energy expended during physical activity and recovery 20

21 4. Components of Energy Expenditure Energy Expenditure During Rest & Physical Activity Basal Metabolic Rate Minimum energy requirement sustains the body s functions. Regular exercise slows a decrease in metabolism with age. Lower in women compared with men 21

22 4. Components of Energy Expenditure Total Daily Energy Expenditure (TDEE) Influenced by: Physical activity Accounts for between 15% and 30% TDEE Dietary-induced thermogenesis Ranges between 5-10% of the ingested food energy Climate Pregnancy 22

23 4. Components of Energy Expenditure The Metabolic Equivalent (MET)- unitless One MET represents an adult s average seated, resting oxygen consumption or energy expenditure. MET provides a convenient way to rate exercise intensity as multiples of resting rate of energy expenditure. 1 MET = 3.5 ml O 2 kg -1 min -1 or ~250 ml O 2 min -1 2 MET activity: ~ 2 x 250 ml O 2 min -1 =500 ml O 2 min -1 to convert MET to kcal min -1, use body weight and 1.0 kcal kg -1 h -1 e.g. 70 kg person cycles at a VO 2 of 2.5 L min -1 or 10 MET 10 MET=10 kcal kg -1 h -1 x70 kg 60 min h -1 =11.7 kcal min -1 23

24 4. Components of Energy Expenditure The Metabolic Equivalent (MET)- Practice Questions For the solutions see: Answers in the online Students Resources 24

25 BPK 312 Nutrition for Fitness & Sport Lecture 4 - Part 2 Summary Slide Measurement of Energy in Food & During Physical Activity 1. Heat of Combustion & Energy Value of Foods 2. Measurement of Human Energy Expenditure a. Direct Calorimetry b. Indirect Calorimetry 3. Respiratory Quotient (RQ), Weir Equation & Respiratory Exchange Ratio (RER) 4. Components of Energy Expenditure 25