Energy Intake and Expenditure L3

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 MethodAccuracy Skinfolds4% 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…  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)