how is energy defined
the capacity to do work or to preform an activity (any physiological process)
what is a calorie (cal)
measure of heat that is used to express the energy content of food
kcal = 1000 calories = 1 Calorie = 1 cal
1 kcal = 4.18 KJ
what is a positive energy balance
- energy IN > energy out
- growth, pregnancy
- weight gain/obesity
- cardiovascular disease
- insulin resistance
what is a negative energy balance
- energy in < energy OUT
- weight loss - over long time –> starvation
- infection
- fever
what is bomb calorimetry
- measures heat produced when a food sample is combusted in a high O2 environment
- works on the principle of direct calorimetry - food is burned completely and heat liberated measured
- dry + weigh sample & place in enclosed chamber w O2
- water surrounds chamber, sample ignited
- heat released absorbed by water & measured
what is heat of combustion
gross energy (GE) - i.e. max amount of energy in sample
what is calorimetry
- measures heat production, allows for estimation of potential energy that was present in food
- measures heat released when foods are burned - provides a direct measure of amount of energy stored in chemical bonds of foods
Describe energy partitioning
- Gross energy (GE) - total food energy (bomb calorimeter)
- energy is lost to feces
- digestible energy (DE) - absorbed food energy
- energy lost to gases (usually ignored in calculation)
- energy lost in urine (protein - N in form of urea)
- metabolizable energy (ME) - useable energy for body - feed directly into metabolic pathways -> ATP
- energy list to HIF
- net energy (NE) - basal metabolism activity, growth, lactation, pregnancy
what are Atwater’s physiological fuel values?
- measure ME
- fat: 9
- protein: 4
- CHO: 4
What is HIF
heat increment of feeding
- aka “thermic effect of food”
- energy expended in digestion, absorption, distribution, and storage of dietary nutrients
what is NE?
net energy
- NE = ME - HIF
what are the three components of total energy expenditure (other than HIF)
- BMR
- physical activity energy expenditure (PAEE)
- thermoregulation (sweating, shivering)
what is Kiebler’s law?
metabolic rate (BMR of animal) proportionate to mass^0.75
What factors affect BMR?
- genetics
- age
- gender
- exercise
- ambient temperatures
Describe direct calorimetry
- energy expenditure can be measured by body heat production
- measures heat a person generates
- need to measure sensible heat loss & insensible losses
- very expensive
- impractical
Describe indirect calorimetry
- all energy releasing rxns in the body depend on the utilization of O2 & the production of CO2
what is RQ?
respiratory quotient - also called RER respiratory exchange ratio
- provides info about energy expenditure & biological substrates being oxidized for energy expenditure
- RQ = CO2 produced / O2 consumed
