Lec4.MeasEnergy.student

8/7/2019 Lec4.MeasEnergy.student

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Professor V. Katch MVS 110: Measurement of Energy

Expenditure

Measurement of Human Energy

Expenditure Understand the following:

Heat of combustion (Calories)

Atwater factors How to measure kCal

Quantify energy release in metabolism

Quantify food mixture metabolized


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Expenditure

What is a Calorie?

A measurement of food energy

Quantity of ____ necessary to raise thetemperature of 1 ___ (1 L) of water 1 degree

___ (from 14.5 to 15.5C) If a food contains 300 kCal then releasing the

potential energy trapped within this foodschemical structure increases the temperture of

300 L of water 1C. Different foods contain different amounts ofheat energy.


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Expenditure

How to Measure Calories?

The Bomb Calorimeter

Figure 1. Bomb calorimeter directly measures the energy value of food.


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Expenditure

Heat of Combustion

The heat liberated by oxidizing (burning)food in a bomb calorimeter represents its

_______ ____ _______ or total energyvalue of the food.

Average heats of combustion

CHO = 4.2 kCalg-1

Lipid = 9.4 kCal g-1

Protein = 5.65 kCalg-1


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Expenditure

Net Energy Value of Foods

Gross energy value from the bomb calorimeter

are different than what happens in the body.

Net energy values equal what is available to thebody after digestion:

CHO =

Lipid = Called Atwater factors

Protein =


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Expenditure

Energy Value of What You Eat

Calculate energy value of a meal

Atwater factor x food grams = total kCal

Go through an example for 100 g of food thatcontains 4% protein (4 g), 13% fat (13 g) and21% CHO (21 g).

[(4 x 4.0) + (13 x 9.0) + 21 x 4.0)]

[16 + 117 + 84 = 217 kCal


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Expenditure

Measuring Human kCal Production

CA LO RIM ET RY

Direct Indirect

CO2 +N2 Balance

Oxygen Consumption

Open Circuit ClosedCircuit

MET ABOLISM


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Expenditure

Measuring Human kCal Production

INDI T L I T D I T L I T

U ITH H T

2

FOODSTUFF + OXYGEN > HEAT + CO2+ H2O


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Expenditure

Measuring Human kCal ProductionDirect Calorimetry [Atwater-Rosa]


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Expenditure

Indirect CalorimetryMeasuring VO2 uptake

[Closed Circuit Method]

Positive:Negative Aspects


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Expenditure

IndirectCalorimetry

[Measure VO2 uptake]

Open Circuit Method

Positive:Negative Aspects


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Expenditure

Direct v Indirect Calorimetry

Calorific Transformation for Oxygen

For every liter (L) of oxygen consumed, 5kCal of energy are transformed

Thus, indirect calorimetry is a goodmeasure of heat production


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Expenditure

What Food is Metabolized?

The Respiratory Quotient (RQ)

RQ =

Every food substance has a specific RQ


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Expenditure

RQ for CHO

RQ =

C6H12O6 + 6 O2 > 6 CO2 + 6 H2O


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Expenditure

RQ for Lipid

RQ =

Between 0.69 and 0.73


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Expenditure

RQ for Protein

RQ =


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Expenditure

RQ for Mixed Foods

RQ =


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Expenditure

Thermal Equivalent of Oxygen

for the RQ RQ = 0.70 = 4.686 kCal per L O2

RQ = 0.84 = 4.85 kCal per L O2

RQ = 1.0 = 5.05 kCal per L O2


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Expenditure

Liters of Oxygen and kCals

1 Liter per min OxygenConsumed

5 kCal per min HeatLiberated

250 mL per min OxygenConsumed

1.25 kCal per min heatliberated

At Rest

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