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Lecture 3

NUTR 3210 Lecture Notes - Lecture 3: Calorimeter, Insulin Resistance, Food Energy

7 pages84 viewsFall 2016

Course Code
NUTR 3210
Jennifer Monk

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NUTR3210 Energy
Important Ideas:
ATP (adenosine triphosphate) = cellular source of energy
Energy is defined as the capacity to do work or to perform an activity
Cellular source is supplied by nutrients in the diet (predominantly macronutrients)
Energy value of food = calorie: measure of heat that is used to express the energy content
of food
kcal = 1000 calories = 1 Calorie = 1 Cal *calories on nutrition facts = kcal
1 kcal = 4.18 KJ
1 Calorie = energy required to raise the temperature of 1 kg (1L) of water by 1 degree
Energy Balance: IN = food and drink; OUT = metabolic and cellular function
Positive balance
o Growth, pregnancy
o Weight gain/ obesity
o Cardiovascular disease
o Insulin resistance
Negative balance
o Weight loss
o Infection
o Fever
Fuel Combustion and Metabolism:
Fuel + O2 CO2 + H20 + HEAT *combustion
Fuel + O2 (ADP+PiATP) + CO2 + H2O *metabolism
o HEAT from metabolism and ADP-ATP = heat from combustion
Heat of combustion = Gross Energy (GE)
Food oxidation follows the same process as combustion in a high oxygen environment
We oxidize nutrient in the presence of metabolic oxygen and ultimately produce carbon
dioxide, water and heat
Estimating the Potential Energy of Foods:
Calorimetry estimates how much energy is in food
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o Bomb Calorimetry measures heat produces when food sample is combusted in a
high oxygen environment
Dry and weigh sample (~1g) and place in enclosed chamber with oxygen
Water surrounds chamber
The sample is ignited and the heat released is absorbed by water and
Heat of combustion = max amount of energy in the sample
Does not take in account energy used for digestion and absorption
over estimates usable energy
Change in water temperature is used to calculate GE
In a bomb calorimeter:
Fat = 9.4 kcal/g
Protein = 5.65 kcal/g
Carbohydrates = 4.13 kcal/g
o Calorimetry measures heat production and allows for the estimation of the
potential energy that was present in the food
Measures heat release
This provides direct measure of the amount of energy stored in the
chemical bonds of foods
o =Gross Energy (GE) or Heat of Combustion of the food
maximum energy which could be obtained when the food is completely
oxidized metabolically or by chemical combustion
Partitioning of Energy from Foods: human body doesn’t fully digest and absorb ALL the the
food energy (cant digest fibre so some energy is not fully extracted)
Gross Energy Energy lost in feces = Digestible Energy (DE)
Digestible Energy Energy lost in urine (nitrogen in the form of urea) = Metabolizable
Atwater’s Physiological Fuel Values Measure Metabolizable (available) Energy
Fat = 9kcal/g
Protein = 4 kcal/g
Carbohydrates = 4 kcal/g
*urea = how the body excretes nitrogen = 1.25
o urine sample can be dried and combusted in a bomb calorimeter and the result is
1.25 kcal/g of the protein that was consumed in the diet
Why does fat provide more kcal/g of Gross Energy than carbohydrates of energy?
CHO ratio of H:O = 2:1
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