Question

What are the two components of body composition, and of what are they composed?

Answer 1

The body is composed of carbohydrate, protein, lipid (fat), water, vitamins, and minerals. The body composition divides the body into a fat component and fat-free component. The method is based on a two compartment model of body composition, fat mass and fat free mass, based on Boyle’s law. Body fat is the most variable constituent of the body. The total amount of body fat consists of essential fat and storage fat. It uses the inverse relationship between pressure and volume to derive body volume for a subject. If both volume and bodyweight are known body density can be calculated by using the following equation:

Body Density = mass/volume, where mass = body weight (kg) and volume = liters (l)

Measurement of %fat by densitometry relies on certain assumptions:

a) The proportions of body compartments other than fat (i.e. those that make up fat-free mass as shown in the image on the right) are relatively constant from person to person.

b) Subjects being measured differ from the reference standards for body composition only in their amounts of body fat.

c) The determination of body composition by densitometry also relies on certain factors that can affect fat-free mass composition and density. These include growth and maturation, physical training, aging, race, and sex. Some or all of these factors need to be taken into account when using densitometry for body composition assessment.