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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
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
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
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
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
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
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
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
How is the physiological fuel value calculated?
(HofC - loss in urine) x apparent digestibility coeff
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
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
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
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
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]
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%)
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
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
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
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
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
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
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
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
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
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
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