Energy Metabolism Flashcards
what is the cellular source of energy?
ATP
- supplied by macronutrients in the diet
- sustains physical energy, anabolism, active transport, etc.
what is the energy value of food?
- a Calorie
- chemistry calorie and food Calorie are different
- 1000 chemistry calories = 1 food Calorie
- 1 food Calorie = 1kcal = 4.18KJ
what is a food calorie?
the energy required to raise the temperature pf 1kg (1L) of water by 1 degree C
what is energy balance
energy in (food and drink) vs. energy out (metabolic and cellular function, physical activity)
what is positive energy balance?
energy in > energy out
results in…
- weight gain/obesity
- infertility
- increased blood lipids
- insulin resistance
what is negative energy balance?
energy in < energy out
results in…
- weight loss
- infection
- loss of performance
- reduced bone mass
Historical perspective of energy intake
Antoine Lavoisier
- compared heat produced by a guinea pig with the production of CO2
- used an ice calorimeter (heat produced estimated by the amount of ice that melts)
- CO2 formed from the rxn between oxygen and organic matter
Justin Liebig
- recognized that protein, CHO and fat are oxidized by the body
Max Rubner
- measured the energy values of certain foods to determine caloric content
what is calorimetry
- measurement of heat production
- used heat as an indicator of the amount of energy stored in the chemical bonds of foods (C-H bonds)
- chemical composition determines how much heat is produced
bomb calorimetry
- dry and weigh sample and place in closed chamber (bomb) with oxygen
- ignite the sample and the heat released is absorbed by water and measured
- the result is heat of combustion: gross energy
what is gross energy
maximum energy
- not necessarily what you will get from calorimetry
potential errors with bomb calorimetry
- overestimates the energy (caloric content) - we do not digest food like a bomb calorimeter
- doesn’t take into account the energy needed for digestion and absorption
physiological fuel values of different nutrients
CHO = 4
Fat = 9
Protein = 4
can calculate from (heat of combustion - energy lost in urine) x apparent digestibility
a = heat of combustion
b = energy lost in urine
c = apparent digestibility
CHO: 4.25, none, 97
Fat: 9.4, none, 95
Protein: 5.65, 1.25, 92
what are different names for physiological fuel values
- available energy
- metabolizable energy
- Atwater value
1 and 2 take into account incomplete digestion
why does fat provide more kcal/g vs. CHO and protein?
- lipids are less oxidized and their ratio of H:O is much greater than 2:1
- lipids have lots of H atoms available for cleavage and oxidation of energy
- CHO have a ratio of 2:1 H:O
- protein has N which combines with H and is eliminated as urea (this loss of H affect heat of combustion)
FA structure and gross energy of stearic acid, oleic acid and linoleic acid
Stearic acid: 18:0, 9.53 kcal/g
Oleic acid: 18:1, 9.48 kcal/g
Linoleic acid: 18:2, 9.42 kcal/g
what are factors that effect heat of combustion for FAs?
chain length: longer chain length releases more energy
degree of unsaturation: more double bonds = less energy released for an equivalent length FA
How do we use Atwater values to determine caloric content?
multiply the amount of a nutrient (fat, protein or CHO) by its atwater value and add the 3 together to get caloric content
- if kcals don’t add up, has to do with the carbs and fibre
what is heat increment feeding?
- includes the different amounts of energy used for digestion, absorption, distribution and storage of nutrients
- comprises 5-30% of daily energy usage
- used too determine net energy (metabolizable energy -HIF)
- also called the thermic effect of food
what is net energy?
supports basal metabolism
- energy required to sustain basic bodily functions such as physical activity, growth and pegnancy
how is energy lost at different stages during metabolism
Gross energy - digestible energy: energy lost in feces (not 100% digested)
- metabolizable energy: gases (ruminants) and energy loss in urine (birds)
- net energy: heat increment of feeding
- net energy then goes towards basal metabolic activity and excess energy ends up being stores in adipose tissue
What are the primary components of energy expenditure
- basal metabolic rate (BMR)
- thermic effect of food (HIF)
- physical activity energy expenditure (PAEE)
- less prominent component is thermoregulation which is the body’s attempt to be at a comfortable temp
physical activity energy expenditure
- included any physical activity, mostly walking
- the more active you are the more energy you need
- amount varies greatly between individuals
what is BMR
- the amount of calories your body uses to support basic functions
- kcal per 24 hours
- largest component of energy expenditure - 60-80%
how is BMR measured?
- shortly after walking (overnight you would be fasting, anything from the last meal is cleared
- post-absorptive state ( not right after a meal)
- lying down
- completely relaxed
- comfortable room temperature
what tissues are most reflective of BMR?
muscle and bone
how do you calculate basic BMR?
BMR = A x [M^0.75] kcal/day
A = metabolically active tissue (fat-free mass - bone and muscle)
- the “A” value for humans is 70
M = body weight in kilograms
0.75 = Kleibers law - a constant used for all vertebrates, invertebrates and unicellular organisms
what is the problem with the basic BMR equation
- does not take into account the different characteristics of individuals (such as muscle mass)
Harris-Benedict equation for BMR
- takes into account biological sex, weight, height, age, physical activity
- improvements made
- a persons BMR decreases with age
BMR vs RMR
- BMR follows strict experimental guide when calculating
- RMR doesn’t require strict guidelines
What factors can affect BMR?
Genetics: inheritance of fast or slow metabolic weight
Age: young > old (greater muscle mass)
Biological sex: men > women (greater muscle mass)
Exercise: changes body tissue proportion
- fat tissue (20% body weight, 5% metabolic activity)
- muscle (30-40% body weight, 25% metabolic activity)
- brain, liver, heart and kidney (5% body weight, 60% metabolic activity - size of these doesn’t change with exercise)
Temperature: maintaining thermoregulation (sweating)
how can you use body fat % to calculate BMR?
- using the Katch-Mcardle BMR equation
- same formula for men and women
- find out body fat % to get a more accurate FFM %
calorimetry: general combustion equation
Fuel + O2 –> CO2 + H2O + Heat
fuel = diet (CHO, fat, prot)
O2 and CO2: measured in indirect calorimetry (looks at gas exchange)
heat : direct calorimetry (bomb calorimeter)
direct calorimetry
- measures the heat a person generates (total heat loss)
- expensive and impractical
indirect calorimetry
estimates energy requirements by measuring…
- oxygen consumption (L)
- carbon dioxide (L)
- urinary nitrogen loss (g) - only in protein approach
- non-protein approach is more common
- this method does not account for anaerobic processes
pros and cons of indirect calorimetry
pros: useful with animals, can determine the type of substrate being oxidized
cons: hyperventilation, hard to get an airtight seal, masks are impractical
what is the respiratory quotient (RQ)
- provides info about energy expenditure and the biological substrate being oxidized
ratio of gas exchange: RQ = CO2 produced/O2 consumed - we use non-protein RQ because protein contributes little to energy metabolism
How do RQ values vary for different macronutrients?
- differences in chemical composition give rise to different amounts of oxygen intake in relation to CO2 produced for each macronutrient
Carbohydrate: RQ = 6 CO2/6 O2 = 1 - carbs require less oxygen
Fat: RQ = 16 CO2/23 O2 = 0.7
range = 0.7-1, anything over1 means the person is hyperventalating
RQ value table
- for each non-protein RQ value there is a caloric value for each L of O2 consumed or CO2 produced
if value is 1, 100% of fuel for energy comes from CHO
of value is 0.7, 100% of fuel for energy comes from fat
assumptions made when using RQ table to answer questions
- only CHO and fat are metabolized
- no synthesis is taking place at the same time as breakdown (no anabolic processes)
- amount of CO2 exhaled = amount of CO2 produced by tissues
Changing RQ: the crossover concept
substrate utilization during exercise: low intensity vs. high intensity
- the crossover point is where CHO-derived fuel use is greater than lipid-derived fuel
- endurance (lipid) vs. high intensity (CHO)
- training will enable a person to move the crossover point to the right, meaning lipid is used more than CHO
