energy Flashcards
(27 cards)
what is the cellular source of energy?
ATP
what is the energy value of a food?
- calorie which is a measure of heat to express the energy content of food
- 1 food calorie: energy required to raise the temp of 1 kg of water by 1 degree C
are chemistry calories and food calories the same?
no, 1000 chemistry calories = 1 food calorie = 1 kcal = 4.18 KJ
what is calorimetry?
- measurement of heat production
- uses heat as an indicator of the amount of energy stored in C-H bonds of foods
what is bomb calorimetry?
- where a sample is ignited in a chamber and the heat released is absorbed by water and measured
- measures gross energy
what is heat of combustion?
gross energy = the maximum amount of energy that will be produced
why does fat provide more kcal per gram than CHO or protein?
- CHO ratio of H to O = 2:1
- protein has N but it combines with H and is eliminated as urea; loss of H affects heat of combustion
- lipids are less oxidized than CHO and protein, ratio of H to O is much greater than 2:1, lots of H for cleavage and oxidation for energy
what are the atwater values of CHO, fat, and protein?
- CHO: 4
- fat: 9
- protein: 4
what are factors that affect heat of combustion of fatty acids?
- chain length: longer chain length releases more energy
- degree of unsaturation: the more double bonds, the less energy released for equivalent chain length FAs
how do you calculate the kcal of CHO, fat, or protein in a sample?
grams x atwater value kcal/g = kcal in sample
what is heat increment of feeding?
- aka thermic effect of food
- energy used for the digestion, absorption, distribution, and storage of nutrients
- 5-30% of daily energy usage
- used to determine net energy
how do you calculate net energy?
net energy = metabolizable energy - HIF
how do you calculate gross energy?
gross energy = kcal/weight in g
how do you calculate metabolizable energy?
metabolizable energy = gross energy x apparent digestibility
what is net energy?
energy that supports basal metabolism, physical activity, growth, pregnancy, etc.
what are the three primary components to energy expenditure?
- basal metabolic rate
- thermic effect of food/hif
- physical activity energy expenditure
(thermoregulation)
how is bmr measured?
- shortly after waking, post absorptive/fasted state, lying down, completely relaxed, and comfortable room temperature
- BMR = kcal per 24 hours
- based on metabolic weight
what is the A constant for humans when calculating BMR?
70
what factors affect BMR?
genetics, age, sex, exercise, temperature
what is indirect calorimetry?
- estimates energy requirements by measuring oxygen consumption, carbon dioxide production, and urinary nitrogen loss
- can’t account for anaerobic processes
what are the disadvantages of indirect calorimetry?
hyperventilation, hard to get an airtight seal, masks are impractical
what are the advantages of indirect calorimetry?
useful with animals, can determine the type of substrate being oxidized
what is the respiratory quotient?
- ratio of metabolic gas exchange
- provides info about energy expenditure and biological substrate being oxidized
how do you calculate the respiratory quotient?
RQ = CO2 produced/O2 consumed
