NUTR 3210 Lecture Notes - Lecture 3: Calorimeter, Insulin Resistance, Food Energy
1 May 2018
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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
Celsius
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
find more resources at oneclass.com
find more resources at oneclass.com
2
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
measured
▪ 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
Energy
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
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Energy balance: in = food and drink; out = metabolic and cellular function: positive balance, growth, pregnancy, weight gain/ obesity, cardiovascular disease, insulin resistance, negative balance, weight loss, infection, fever. Over estimates usable energy: change in water temperature is used to calculate ge. 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. *the bomb calorimeter measures the total energy potential of a compound. Total energy expenditure: components, hif (more constant, basal metabolic rate (largest part of energy expenditure; ~60% of energy, physical activity energy expenditure (variable, thermoregulation (variable) How to estimate bmr across diverse species: kleiber"s law: the metabolic rate is directly proportional to mass(or surface area)0. 75, *this is an estimate; does not work well for humans too much variability.
