Chapter 8 Measurement of Human Energy Expenditure (p. 177-189)
All metabolic processes within the body result in heat production.
Energy input (food consumption) relates to energy expenditure, verifying the law of the conservation
of energy.
Calorie: basic unit of heat measurement
Calorimetry: measurement of heat transfer
Direct Calorimetry (limited practical applications)
- Atwater-Rosa calorimeter: Chamber in where a test subject could live, eat, sleep and exercise on
a bicycle ergometer.
- Airflow calorimeter: temperature change in air that flows through an insulated space, multiplied by
the air’s mass and specific heat, including calculations for evaporative heat loss = heat production
- Water flow calorimeter: “, but change in temperature occurs in water flowing through coils that
make up part of an environmentally self-contained body suit worn by astronauts.
- Gradient layer calorimetry: measures body heat that flows from the subject through a sheet of
insulating materials with appropriate piping and cooler water flowing on the outside of the gradient.
Indirect Calorimetry (simpler, less expensive)
All energy-releasing reactions in humans depend on oxygen use. 5.0 Kcal per liter of oxygen
consumed for the energy expenditure under steady-rate conditions of aerobic metabolism.
- Closed-circuit Spirometry: subject breathes 100% oxygen from prefilled container or spirometer
and rebreathes it. Canister of potassium hydroxide in the breathing circuit absorbs exhaled Co2. A
drum records the oxygen removed from changes in the system’s total volume.
- Open-circuit Spirometry: subject inhales ambient air (20,93% O2, 0,03% Co2 and 79,04% N2).
Changes in exhaled O2 and Co2 reflect the process of energy metabolism. Therefore analyse 1)
volume of inspired and expired air breathed during a specified time and 2. composition of inspired and
expired air to measure oxygen consumption and infer energy expenditure.
1. Portable Spirometry: include whole-body multisensor devices. In these applications, an integrated
computer performs the metabolix calculations based on electronic signals it receives from micro-
designed instruments that measure O2 and Co2 in expired air, and respiratory flow dynamics and
volumes.
2. Bag technique: Two way, high-velocity, low-resistance breathing valve. Subject breathes ambient
air through one side of the valve and expels it through the other side, into a large Douglas bag, a
rubber meteorological balloon or directly through a gas meter that continuously measures expired air
volume. Meter draws a sample for analysis of O2 and Co2 composition.
3. Computerized Instrumentation:
- System to continuously sample subject’s expired air volume
- O2 and co2 analyzers to measure expired gas mixture’s composition
Computer performs metabolic calculations, producing a printed/graphic display of the data
Micro-Scholander technique: measures O2 and Co2 concentration in expired air to an accuracy of
+- 0.015 mL per 100 mL of gas. (0.5 mL gas in 10 min)
Haldane method: uses larger air sample (10-15 min)
Double labeled water technique: method to estimate total average daily energy expenditure in free-
living conditions. Subject consumes a quantity of water with a known concentration of the heavy,
nonradioactive forms of the stable isotopes of hydrogen (H) and O. Isotopes distribute throughout
bodily fluids. Labeled hydrogen leaves the body as water and labeled oxygen as water and Co2
produced during macro-nutrient oxidation in energy metabolism. Differences between elimination
rates of the two isotopes relative to the body’s normal background levels estimate total CO2
production during the measurement period. Oxygen consumption is easily estimated on the basis of
,CO2 production and an assumed respiratory quotient of 0.85. Analysis of unire/saliva before
consuming doubly labeled water serves as control baseline values for O and H. Researchers measure
enriched urine/saliva intitially and then every day/week The progressive decrease in sample
concentrations of the two isotopes permits computation of the CO2 production rate.
Respiratory quotient (RQ) = Co2 produced / O2 consumed
RQ describes the ratio of metabolic gas exchange to approximate the nutrient mixture catabolized for
energy during rest and aerobic physical activity. This assumes that the exchange of O2 and Co2
measured at the lungs reflects gas exchange from macronutrient catabolism in the cell. This remeans
reasonable during rest and steady-rate conditions with little reliance on anaerobic metabolism.
- Carbohydrate: C6H12O6 + 6 O2 → 6 Co2 + 6 H2O. RQ = 6 Co O2 = 1.00
- Fat: C16H32O2 + 23 O2 → 16 Co2 + 16 H2O. RQ = 16 Co2/23 O2 = 0,696
- Protein: C72H112N2O22S + 77 O2 → 63 Co2 + 38 H2O + SO3 + 9CO(NH2)2
RQ = 63 Co O2 = 0,818
- Non protein: portion of respiratory exchange attributed to the combustion of only carbohydrate and
fat excluding protein. Subject consumes 4.0L of O2, produced 3.4L of Co2 during 15-min rest period.
Kidneys excrete 0.13g nitrogen in urine.
1. 4.8 L Co2 per g protein metabolized x 0.13 g = 0.62 L Co2 produced in protein catabolism
2. 6.0 L O2 per g protein metabolized x 0.13 g = 0.78 L O2 consumed in protein catabolism
3. Nonprotein Co2 produced = 3.4 L Co2 - 0.62 L Co2 = 2.78 L Co2
4. Nonprotein O2 consumed = 4.0 L O2 - 0.78 L O2 = 3.22 L O2
5. Nonprotein RQ = 2..22 = 0.86
For most purposes assume an RQ of 0.82 (metabolism of a mixture of 40% carbohydrate and 60%
fat) and apply the caloric equivalent of 4.825 kcal per liter of O2 for energy transformations.
Respiratory Exchange Ratio (RER): ratio of carbon dioxide produced to oxygen consumed
under non-standard situations.
In the pulmonary capillaries, carbonic acid degrades to co2 and h2. The RER increases
above 1.00 because buffering adds extra nonmetabolic-created Co2 to expired air above
the quantity normally released during energy metabolism.
HLa + NaHCO3 → NaLa + H2CO3
H2CO3 → H2O + Co2 → Lungs
Relative low RER can occur following exhaustive physical activity, the cells and bodily
fluids retain Co2 to replenish the sodium bicarbonate that buffered the accumulating
lactate.
, Chapter 9: Human energy expenditure during rest and physical activity (p. 191 - 203)
Metabolism involves all chemical reactions that encompass anabolism (synthesis) and catabolism
(breakdown). Following factors affect total daily energy expenditure (TDEE)
1. Thermogenic effect of feeding
2. Thermic effect of physical activity
3. Resting metabolic rate
Combined these three comprise the dietary energy requirements for nongrowing individuals.
Basal metabolic rate(BMR/ Basal energy expenditure BEE): minimal level of energy to sustain vital
functions in the waking state. Reflects sum total of the body’s many avenues for heat production.
- Postabsorptive (fasting) state without food for 12-18 previous hours
- No physical activity for minimum of 2 hours prior
- 30 min rest in lab in comfortable, thermoneutral environment
- 10 min oxygen consumption measurement
Oxygen values range between 160 and 290 mLxmin^-1 (0.8 to 1.43 kcalxmin^-1)
Resting metabolic rate (RMR):
- 3-4 hours after a light meal without prior physical activity
RMR accounts for 60-75% of TDEE, thermic effects from eating for 10% and physical activity 15-30%.
The surface area law: expressing basal or resting metabolic rate (energy expenditure) by body
surface area (in quare meters) per hour (kcal x m^-2 x hr^-1). Does not apply universally.
Concept of metabolic size related basal metabolism to body mass raised to the 0.75 of power. BMR
expressed relative to body mass is true for humans/wide variety of mammals.
For an individual/group of the same gender, body surface area provides as good as an index of RMR
as does FFM, because of the strong within-gender association between body surface area and FFM.
Females 5-10% lower RMR than males, because more body fat and less fat-free tissue. Changes in
body composition explain the 2-3% per decade BMR reduction for man and woman.
Regular endurance and resistance exercise offsets the decrease in resting metabolism that usually
accompanies aging. Maintaining FFM during weight reduction counters the potential negative effects
of weight loss on exercise performance.
Total metabolic rate per hour = BMR value x calculated surface area.
Body surface are (BSA, m²) = H⁰,⁷²⁵ X W⁰,⁴²⁵ X 71,84
H= Stature (cm), W= mass (kg)
To determine BSA from nomogram, locate stature on scale I and body mass on scale II, intersect on
scale III.
DeltaBMR = (measured BMR - standard BMR) x 100 / standard BMR
Any value within +-10% of the standard represents a normal BMR.
Resting daily energy expenditure (RDEE): BMR value X BSA X 24(hours)
Waarom staat er RDEE (kcal) = 370 + 21.6 (FFM, Kg)
Factors affecting TDEE:
1. Physical activity: exerts the most profound effect on human energy expenditure (15-30%).
2. Diet-induced Thermogenesis (DIT/ Thermic effect of food (TEF)) consists of obligatory
