Nutrition 3210

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Nutrition 3210
2012-02-13 15:17:49
Energy Metabolism

midterm week 3
Show Answers:

  1. What is the cellular source of energy and how is it supplied?
    What is the energy value of food? How is it measured?
    • ATP - supplied by nutrients in the diet - mostly macronutrients
    • Calorie (cal): measure of heat contained in chemical bonds of food
    • 1Cal = 1kcal = 1000 calories = 4.19kJ
  2. How does energy come in and out? What is positive energy balance, negative energy balance and basal energy?
    • Energy comes in through food and drink and goes out through metabolic and cellular functions
    • Positive energy balance: weight gain/obesity or pregnancy - in>out
    • Negative energy balance: weight loss or infection/illness - in < out
    • Basal energy requirement to sustain life
  3. How are potential energy of foods estimated?
    • Calorimetry = measurement of heat production
    • Use heat as an indicator of the amount of energy stored in the chemical bonds of foods (C-H bonds - oxidizing food)
    • Bomb calorimetry: measures heat released when foods are burned
  4. How is bomb calorimetry used to estimate food energies?
    • 1. Dry and weight sample and place in enclosed chamber with oxygen
    • 2. Sample ignited and bonds are broken
    • 3. Heat released is absorbed by water and measured as a change in water temperature
    • 4. heat combustion - represents TOTAL or GROSS ENERGY value o the food
    • However this is different then what the body can take in - we are nto as efficient
  5. Why does fat provide more kcal per g then carbs or proteins?
    • Based on the chemical structure
    • Carbs have a H:O ratio of 2:1
    • In lipids the ratio is > 2:1 thus lipids have more Hs that can be cleaved away and oxidized to generate energy
  6. What is the heat of combustion, apparent digestibility coeff. and physiological fuel value of CHO?
    • HofC: 4.15 kcal/g
    • ADC: 97%
    • PFV: 4 kcal/g
  7. What is the heat of combustion, apparent digestibility coeff. and physiological fuel value of fat?
    • HofC: 9.40 kcal/g
    • ADC: 95%
    • PFV: 9kcal/g
  8. What is the heat of combustion, loss in urine, apparent digestibility coeff. and physiological fuel value of proteins?
    • HofC: 5.65kcal/g
    • loss in urine: 1.25 kcal/g (in body N is not oxidized therefore excreted)
    • ADC: 92%
    • PFV: 4 kcal/g
  9. How is the physiological fuel value calculated?
    (HofC - loss in urine) x apparent digestibility coeff
  10. What is gross energy and metabolizable energy? How are each calculated? Give an example of 2 FA in diet and explain why their values vary.
    • Gross energy: total amount of energy possible from a nutrient - divide energy released in bomb calorimetry by molecular weight
    • Meta. energy: amount of energy that it absorbed in the diet - multiply the GE by the ADC
    • All FA are different chain lengths therefore different energy values ex: stearic acid (18 C saturated FA common in diet VS butyric acid )
    • For all FA in diet, GE and ME have been calculated and they have been weighted averaged
  11. How can ME be calculated on a food label? Why are carbs ME value an overestimation?
    • Multiply mass on label by PFV
    • Carbs are an overestimation because it includes dietary fibre which is not digestible therefore not supplying 4kcal/g directly however it is generall included
  12. What is Heat increment of feeding (HIF)?
    • Thermic energy of food
    • Energy expended in digestion, absorption (ATP dependent mechanisms), distribution and storage of dietary nutrients
    • 5-30% expenditure
    • Subtracted from ME to yield net energy
  13. What is net energy? Which digestive system has a high energy investment?
    • Supports basal metabolism, physical activity, growth, pregnancy, etc.
    • Ruminant digestive system is a lot more E investment - HIF is higher
    • depends on nutrient composition of diet - high protein means high HIF because N isn't oxidized
  14. Describe the partitioning of energy from foods.
    Gross energy - [lose fecal energy - non digestible nutrients] -> digestible energy - [lose gases and urinary energy] -> Metabolizable energy - [used for heat increment of feeding] -> net energy - [used for basal metabolic acitivity]
  15. What are the 3 components to energy expenditure?
    • 1. Basal metabolic rate (BMR) - 60-75%
    • 2. Thermic effect of food (TEF) or also called HIF - 5-10%
    • 3. Physical acitivity energy expenditure - variable and have most control over (20-30%)
  16. In what conditions must BMR be measured? What does the BMR measure?
    • Shortly after waking
    • post-absorptive state (fasted state ensures no conribution of thermic effect)
    • Lying down - no physical activity
    • Completely relaxed
    • Comfortable room temperature - no thermogenesis
    • BMR = kcal/24hrs
    • Measure how many cal need to keep stable weight then consider physical activity
  17. How do you calculate BMR?
    • BMR = A x [M0.75] kcal/day
    • A - metabolically active tissue rather than body weight (there are factors for species that predict this)
    • M - body weight in kg
    • 0.75 - Kleiber's law - used fr all vertebrates, invert. and even unicellular organisms
  18. what are some factors that affect BMR?
    • genetics: inheritance of fast or slow BMR
    • age: young > old becuse greater mass of metabollically active muscle
    • sex: men > women because greater muscle mass
    • Exercise: changes body tissue proportions (adipose tissue decreases and muscle increases)
    • Temperatures: maintaining thermoregulation
  19. How is total energy expenditure measured?
    • All metabolic processes in the body generate heat
    • Heat production can be used as a measure of energy expenditure
    • Can use diect calorimetry or indirect calorimetry
  20. What is direct calorimetry?
    • Measures the heat a person generates - total ehat loss
    • Very expensive and impractical
    • Put a human in a giant human calorimeter to directly measure caloric expenditure
  21. What is indirect calorimetry?
    • More accurate
    • Energy releasing reactions in the body depend on utlization of oxygen - assumption
    • estimates heat production by measuring:
    • 1. Oxygen consumption (L)
    • 2. CO2 production (L)
    • *These are the most important
    • 3. Urinary nitrogen loss (g) - not always measured because assumed mostly carbs and fats are oxidized
  22. What is the respiratory quotient (RQ) and how is it determined? What information does it provide?
    • Determined from indirect calorimetry
    • provides information about energy expenditure and biological substrate being oxidized
    • ratio of metabolic gas exchange: RQ = CO2 produced / O2 consummed
  23. Why do RQs vary for macronutrients? What are the values for CHO and fats and what can this indicate?
    • They vary because there are differences in chemical composition meaning that each macronutrient requires a different amount of oxygen uptake in relation to CO2 produced
    • CHO RQ = 1 - value if purely carbs
    • Fat RQ = 0.7 - value if purely fats
    • Depending on RQ value can tell if primarily fats or CHO
  24. What does the conversion RQ table show us?
    • For each non-protein RQ value, there is a corresponding caloric value for each L of O2 consummed or CO2 produced
    • This table shows us that knowing the nonprotein RQ tells us information about the substrate being oxidized for energy
  25. How is RQ used to determine energy expenditure?
    • 1. Calculate RQ by CO2/O2
    • 2. Use the table to find the conversion factors for O2 and CO2 - multiply the conversion factor by the amount of O2 consummed or CO2 produced - should get the same number
    • 3. Multiply the calories consummed/produced per hour by 24 to find the basal energy requirement/expenditure in the day