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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
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
26
what tissues are most reflective of BMR?
muscle and bone
27
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
28
what is the problem with the basic BMR equation
- does not take into account the different characteristics of individuals (such as muscle mass)
29
Harris-Benedict equation for BMR
- takes into account biological sex, weight, height, age, physical activity - improvements made - a persons BMR decreases with age
30
BMR vs RMR
- BMR follows strict experimental guide when calculating - RMR doesn't require strict guidelines
31
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)
32
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 %
33
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)
34
direct calorimetry
- measures the heat a person generates (total heat loss) - expensive and impractical
35
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
36
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
37
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
38
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
39
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
40
assumptions made when using RQ table to answer questions
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
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

NUTR 3210 (12 decks)

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