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NUTR 3210 > Energy Metabolism > Flashcards

Energy Metabolism Flashcards

1
Q

what is the cellular source of energy?

A

ATP
- supplied by macronutrients in the diet
- sustains physical energy, anabolism, active transport, etc.

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2
Q

what is the energy value of food?

A
  • a Calorie
  • chemistry calorie and food Calorie are different
  • 1000 chemistry calories = 1 food Calorie
  • 1 food Calorie = 1kcal = 4.18KJ
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3
Q

what is a food calorie?

A

the energy required to raise the temperature pf 1kg (1L) of water by 1 degree C

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4
Q

what is energy balance

A

energy in (food and drink) vs. energy out (metabolic and cellular function, physical activity)

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5
Q

what is positive energy balance?

A

energy in > energy out
results in…
- weight gain/obesity
- infertility
- increased blood lipids
- insulin resistance

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6
Q

what is negative energy balance?

A

energy in < energy out
results in…
- weight loss
- infection
- loss of performance
- reduced bone mass

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7
Q

Historical perspective of energy intake

A

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

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8
Q

what is calorimetry

A
  • 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
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9
Q

bomb calorimetry

A
  • 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
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10
Q

what is gross energy

A

maximum energy
- not necessarily what you will get from calorimetry

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11
Q

potential errors with bomb calorimetry

A
  • 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
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12
Q

physiological fuel values of different nutrients

A

CHO = 4
Fat = 9
Protein = 4
can calculate from (heat of combustion - energy lost in urine) x apparent digestibility

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13
Q

a = heat of combustion
b = energy lost in urine
c = apparent digestibility

A

CHO: 4.25, none, 97
Fat: 9.4, none, 95
Protein: 5.65, 1.25, 92

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14
Q

what are different names for physiological fuel values

A
  1. available energy
  2. metabolizable energy
  3. Atwater value
    1 and 2 take into account incomplete digestion
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15
Q

why does fat provide more kcal/g vs. CHO and protein?

A
  • 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)
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16
Q

FA structure and gross energy of stearic acid, oleic acid and linoleic acid

A

Stearic acid: 18:0, 9.53 kcal/g
Oleic acid: 18:1, 9.48 kcal/g
Linoleic acid: 18:2, 9.42 kcal/g

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17
Q

what are factors that effect heat of combustion for FAs?

A

chain length: longer chain length releases more energy
degree of unsaturation: more double bonds = less energy released for an equivalent length FA

18
Q

How do we use Atwater values to determine caloric content?

A

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

19
Q

what is heat increment feeding?

A
  • 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
20
Q

what is net energy?

A

supports basal metabolism
- energy required to sustain basic bodily functions such as physical activity, growth and pegnancy

21
Q

how is energy lost at different stages during metabolism

A

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

22
Q

What are the primary components of energy expenditure

A
  1. basal metabolic rate (BMR)
  2. thermic effect of food (HIF)
  3. physical activity energy expenditure (PAEE)
    - less prominent component is thermoregulation which is the body’s attempt to be at a comfortable temp
23
Q

physical activity energy expenditure

A
  • included any physical activity, mostly walking
  • the more active you are the more energy you need
  • amount varies greatly between individuals
24
Q

what is BMR

A
  • the amount of calories your body uses to support basic functions
  • kcal per 24 hours
  • largest component of energy expenditure - 60-80%
25
Q

how is BMR measured?

A
  • 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
26
Q

what tissues are most reflective of BMR?

A

muscle and bone

27
Q

how do you calculate basic BMR?

A

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

28
Q

what is the problem with the basic BMR equation

A
  • does not take into account the different characteristics of individuals (such as muscle mass)
29
Q

Harris-Benedict equation for BMR

A
  • takes into account biological sex, weight, height, age, physical activity
  • improvements made
  • a persons BMR decreases with age
30
Q

BMR vs RMR

A
  • BMR follows strict experimental guide when calculating
  • RMR doesn’t require strict guidelines
31
Q

What factors can affect BMR?

A

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)

32
Q

how can you use body fat % to calculate BMR?

A
  • using the Katch-Mcardle BMR equation
  • same formula for men and women
  • find out body fat % to get a more accurate FFM %
33
Q

calorimetry: general combustion equation

A

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)

34
Q

direct calorimetry

A
  • measures the heat a person generates (total heat loss)
  • expensive and impractical
35
Q

indirect calorimetry

A

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

36
Q

pros and cons of indirect calorimetry

A

pros: useful with animals, can determine the type of substrate being oxidized
cons: hyperventilation, hard to get an airtight seal, masks are impractical

37
Q

what is the respiratory quotient (RQ)

A
  • 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
38
Q

How do RQ values vary for different macronutrients?

A
  • 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
39
Q

RQ value table

A
  • 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
40
Q

assumptions made when using RQ table to answer questions

A
  1. only CHO and fat are metabolized
  2. no synthesis is taking place at the same time as breakdown (no anabolic processes)
  3. amount of CO2 exhaled = amount of CO2 produced by tissues
41
Q

Changing RQ: the crossover concept

A

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

NUTR 3210 (12 decks)

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