Energy Intake and

ExpenditureL3

Energy Intake

The amount of calories consumed per day

Measured in:

Calories (Kcal) – The amount of energy required to heat up 1000ml of water by 1 degree centigrade

Joules (J) - energy expended, by a force of one newton moving an object one metre along the direction of the force

Energy Expenditure

The amount of calories used per day

REMEMBER: This should balance your intake if you want to maintain your weight, or be more than your intake if you want to lose weight

Body Composition

The body is composed of two elements:

1. Lean body tissue (ie. Muscles, organs, bones, blood)

2. Body fat (or adipose tissue)

The proportion of these two components in the body is called body composition

This is more important than total weight

How can you measure body fat?

1. Skinfold Measurement

2. Underwater weighing

3. Bio-electrical Impedence

4. Near-infra-red interacterance

1. Skinfold Measurement

Skinfold measurements taken at various places on the body (four most common are triceps/biceps/subscapular/suprilliac)

The sum of these measurements is read off an equation chart, which then gives a body fat %

Allowances made for age and sex in equations

What may be the drawbacks of this method?

2. Underwater weighing

A person is weighed when submerged underwater, then again on dry on land

The two readings are used to calculate body density, the principle being that fat is more buoyant than muscle or bone.

Generally considered the gold standard but very expensive

3. Bio-electrical impedance

An electrode is attached to the foot and hand, and a very mild electrical current passed between them.

Body fluids and electrolytes conduct the current.

Body fat creates a resistance, so the body fat % can be calculated by the amount of electrical impedance met.

4. Near-infra-red interactance

An infra red beam is shone perpendicularly through the upper arm.

The amount of light reflected back to the analyser from the bone depends on the amount of fat in the arm, which is correlated to body fat %

Age, weight, height, sex, activity level are all taken into account in calculations.

How accurate are these methods?

Underwater weighing most accurate for athletes

Skin fold measurements second most accurate

Method AccuracySkinfolds 4%

Underwater weighing

3%

Electrical impedance

>5%

Near-infra red

5-10%

Calorimetry

Calorimetry is the science of measuring the heat of chemical reactions or physical changes.

Calorimetry involves the use of a calorimeter.

Direct calorimetry

Directly measures energy produced by combination of food with oxygen

Involves the burning of food in a controlled way, and measuring heat energy produced

Heat energy is measured by observing the rise in temperature of a quantity of water heated by the burning food.

Alternative: Measure body’s heat production in a calorimeter chamber The heat energy created by the subject radiates to

the walls and heats the water. Temperatures of incoming and outgoing water and

air are recorded and used to calculate BMR and total energy expenditure.

Indirect Calorimetry

Uses the fat that every atom of carbon in food combines with a molecule of oxygen during the chemical reaction to produce one molecule of carbon dioxide and release a definite and constant amount of energy.

Similarly, two hydrogen atoms in food combine with one atom of oxygen to produce one molecule of water and release a different but also constant amount of energy.

Method involves the measurement of the amount of oxygen consumed – which can therefore be related to the amount of energy released by food

For example…

134.4 litres of oxygen will oxidise 180g of glycogen to release 2867kJ of heat energy

Therefore, for all food feuls, one litre of oxygen produces 22kJ of heat energy.

Measuring carbon dioxide production and oxygen consumption by calculating the respiratory exchange ratio (RER)