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Lecture 4

BIOL 2P97 Lecture Notes - Lecture 4: Adipocyte, Weight Loss, Polyphagia

Biological Sciences
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Chapter 22: Metabolism and Energy Balance
Energy in the Body: Energy input (diet) = energy output
Energy input: DIET- hunger, satiety, social and psychological factors
Energy output: HEAT- (50%) unregulated; thermoregulation
WORK- (50%) transport across membranes, mechanical and chemical
-energy in food is usually measured in kcal
-1 kilocalorie (=1 Cal which is equal to 1000 calories) is the amount of heat needed
to raise the temp of 1kg of water by 1 degree celcius
-the caloric content of any food can be calculated by remembering 3 simple
-Carbohydrates: 4 kcal/g
-Protein: 4 kcal/g
-Fat: 9 kcal/g
Example of calculating the caloric content:
A plain bagel contains 2g fat, 7g protein, 38g Carbs
2g fat x 9 kcal/(2g fat) = 18 kcal
7g protein x 4 kcal/(7g protein) = 28 kcal
38 Carbs x 4 kcal/(38g carbs) = 152 kcal
How much energy do you use?
Metabolic rate: an individuals energy expenditure
Basal metabolic rate (BMR): an individuals lowest metabolic rate (just so you can
stay living); during sleep
-di<cult to measure accurately
Measuring metabolic rate
-metabolic rate is often measured after a 12 hour fast in a person who is awake but
resting (resting metabolic rate – RMR)
-metabolic rate is estimated using O2 used, CO2 produced, the ratio of CO2
expelled/O2used is often used (called respiratory quotient)
-the ratio of CO2/O2 depends on the composition of the diet
-respiratory quotient changes depending on the food consumed: (CO2/O2=1 for
-Carb: 1 Pure protein: 0.8 Pure fat: 0.7 Avg American diet: 0.82
-this tells us that on average, you produce 0.82 of CO2 for every 1L O2 consumed
-the energy released from di@erent foods is relatively constant
-4.5-5kcal of energy for each 1L of O2 consumed
Example of measuring metabolic rate
-70kg male consumes 430L O2 per day
-assume 1L of O2 is needed for each 4.8 kcal metabolized
Estimated metabolic rate: 430L O2/day x 4.8 kcal/L O2 = 2064 kcal/day (rough
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