NUTR 3210 Lecture Notes - Lecture 3: Indirect Calorimetry, Atwater System, Basal Metabolic Rate
27 Jun 2018
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Heat increment of feeding
oObligatory energy expenditure in digestion, absorption, distribution and storage
of dietary nutrients
oDetermines differences between metabolizable energy (ME) and net energy
(NE)
oWill use 5-10% of the ME content of the meal (lowest for fats, highest for
proteins)
oAbout 10% of total energy expenditure on average
Basal metabolic rate (BMR)
oHighest component of energy expenditure (about 60% of total energy
expenditure)
oMeasured shortly after awakening, about 12 hours after eating, lying down, in a
comfortable temperature room
oMost influenced by lean mass (muscle, bone, organs)
oIs not a constant, and is influenced by multiple factors
oAverage is 1800 kcal/ day or 75kcal/ day
oEquations can be used to estimate BMR
Kleiber's law: shows that BMR is related to surface area, rather than
body weight, in many species
Harris Benedict equations: shows that height, weight, age and gender
predict BMR (experimentally derived)
Physical activity
oHighly variable between individuals
oAccounts for about 30% of total energy expenditure on average
oMuch higher in early human; modernization has increased sedentary behaviours
oSubstrate used during physical activity is dependent on exercise intensity
Thermoregulation
oAbout 10% of total energy expenditure on average
oMuch higher in early humans; modernization with air conditioning and heating
has decreased the need to thermoregulate
Measurement of energy expenditure
oEnergy expenditure can be measured directly through heat production (direct
calorimetry), or indirectly through the measurement of gas exchange and possibly
urinary nitrogen production (indirect calorimetry). Regardless of the approach use, the
same principle of combustion applies: fuel is oxidized in the presence of oxygen, and
carbon dioxide, water, and heat are produced
Direct calorimetry
oMeasures heat production (sensible heat) as well as the heat of evaporation
(insensible heat) using the same principles as in bomb calorimetry. Basically, a person is
put in a giant "bomb" (room) and energy expenditure can be determined by measuring
the temperature change of the water in the walls of the room. This type of calorimetry is
difficult to conduct, and is rarely done anymore
Indirect calorimetry
oMeasures respiratory gas exchange. The basis for indirect calorimetry is that all
energy-releasing reactions in the body depend on the utilization of oxygen and the
production of carbon dioxide. When body fuel (comprised of macronutrients) is
expended, oxygen is consumed and carbon dioxide is produced. The ratio of CO2
produced to O2 consumed is called the respiratory quotient (RQ) and can predict what
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Document Summary
Obligatory energy expenditure in digestion, absorption, distribution and storage of dietary nutrients o (ne) o. Determines differences between metabolizable energy (me) and net energy. Will use 5-10% of the me content of the meal (lowest for fats, highest for proteins) o. Highest component of energy expenditure (about 60% of total energy expenditure) o. Measured shortly after awakening, about 12 hours after eating, lying down, in a comfortable temperature room o o o o. Most influenced by lean mass (muscle, bone, organs) Is not a constant, and is influenced by multiple factors. Average is 1800 kcal/ day or 75kcal/ day. Kleiber"s law: shows that bmr is related to surface area, rather than body weight, in many species. Harris benedict equations: shows that height, weight, age and gender predict bmr (experimentally derived) Accounts for about 30% of total energy expenditure on average. Much higher in early human; modernization has increased sedentary behaviours. Substrate used during physical activity is dependent on exercise intensity.
