bpk 312 lec 4 (chap 6) part 2 - sfu.ca - simon fraser universitymwhite1/bpk 312 lec 4 (chap 6) part...

Measurement of Energy in Food & During Physical Activity

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BPK 312 Nutrition for Fitness & Sport

Lecture 4 - Part 2

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

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)

2 Fig 6.1: A Bomb Calorimeter

1.   Heat of Combustion & Energy Value of Foods

Heat of Combustion (HOC )

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

•  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


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 NH2-CO-NH2

§  ↓ chemical energy from protein; reduces HOC by 19% from 5.65 kcal/g to 4.6 kcal/g

§  CHO & lipids HOC = net energy value

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Net Physiological Energy of Macronutrients

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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 192% (71.6%) x 5.65= 4.05 •  Lipid 95% x 9.4 = 8.93 •  CHO 97% x 4.15 = 4.03

1adjusted for energy loss in urine, this reduces the net energy available from 5.2 (i.e. 0.92 x 5.65) to 4.05 kcal/g

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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)

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.

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2. Measurement of Human Energy Expenditure

Food + O2 CO2 + H2O + ATP + heat

Aerobic metabolism:

Direct Calorimetry

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a) Direct Calorimetry

Fig 6.3: Atwater-Rosa Whole Body human calorimeter


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

•  Doubly labeled water technique

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Food+ O2 CO2 + H2O + ATP + heat

Aerobic metabolism:

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

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b) Indirect Calorimetry 2. Measurement of Human Energy Expenditure

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b) Indirect Calorimetry

Fig 6.4: Closed circuit Spirometry filled with 100% oxygen


Portable Spirometry & Bag Technique

§  Portable spirometry •  Ambient air passes through a two-

way 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.

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Fig 6.5:

Computerized Instrumentation Computer interfaces with

•  A flow-measuring device that records air volume breathed

§ O2 & CO2 analyzers that measure the composition of the expired gas mixture

§ Mouth piece/nose clip or hood

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Fig 6.4:



Fig 6.6: Computerized instrumentation for indirect calorimetry

Fig 6.7: Ventilated hood, Open circuit spirometry

Doubly Labeled Water Technique

§  An good way to assess total EE over prolonged periods

§  ingest water, equilibrate, initial sample, 7-14 later final sample

§  predicts Co2 production to within 3-8%

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2. Measurement of Human Energy Expenditure 18O

H 3H (Doubly-labeled water)

•  3H lost as body H2O in urine, sweat, & w/ breathing •  18O is lost as H2O & CO2 •  Use an est. RQ=VCO2/VO2=0.85 & known/measured CO2 prod. rate e.g. RQ =0.85 & VCO2 = ~0.2 L/min

VCO2= 288 L/day x 6 days = 1728 L/6 days VO2=VCO2/RQ = 1728 L over 6 days/0.85 =2033 L VO2 over 6 days With RQ = 0.85 & ~5 kcal expended/ L O2 EE = 2033 L x 5 kcal/L = 10,165 kcal expended over 6 days

isot

ope

in b

ody

time

18O

3H

Initial sample

Final sample

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 CO2 production, estimated VO2

§  Expensive for isotopes and lab set up with isotope ratio mass spectrometers etc

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2. Measurement of Human Energy Expenditure 18O

H 3H (Doubly-labeled water)

3. The Respiratory Quotient (RQ), Weir Equation & Respiratory Exchange Ratio (RER)

§  The ratio of carbon dioxide produced to oxygen consumed

RQ = CO2 produced ÷ O2 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.

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3. The Respiratory Quotient (RQ), Weir Equation & Respiratory Exchange Ratio (RER) Weir Equation •  calculation of caloric expenditure from ventilation (VE) & % O2EXPIRED •  EE (kcal/min) = VE X [1.044 – (0.0499 X % O2EXPIRED)] •  Value in square brackets ‘[ ]’ = Weir Factor,

-  e.g. VE = 50 L/min, O2EXPIRED =16% -  EE (kcal/min) = 50 x [1.044 – 0.0499 x 16] = 12.3 kcal/min

Weir Eqn: assumes constant energy transfer from protein of 12.5%

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

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• 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 4.825 kcal/ L O2; max error for estimate is ~3-5%

e.g. Exercise for 30 min VO2 = 3.22 L/min VCO2 = 2.78 L/min RQ = 2.78/3.22 = 0.86 EE = 3.22 L O2/min x 4.875 kcal/L O2

= 15.70 kcal/min x 30 min = total of 471 kcal expended


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

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4. Components of Energy Expenditure

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

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Energy Expenditure During Rest & Physical Activity


Total Daily Energy Expenditure (TDEE)

§  Influenced by:

•  Physical activity

§  Accounts for between 15% and 30% TDEE

•  Dietary-induced thermogenesis

§  Ranges between 10% and 35% of the ingested food energy

•  Climate

•  Pregnancy

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The Metabolic Equivalent (MET)- unitless

§  One MET represents an adult’s average seated, resting oxygen consumption or energy expenditure.

1 MET = 3.5 mL[O2]•kg-1•min-1

§  MET provides a convenient way to rate exercise intensity with respect to a resting baseline.

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Measurement of Energy in Food &

During Physical Activity

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BPK 312 Nutrition for Fitness & Sport

Lecture 4 - Part 2 Summary Slide

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

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