body fat

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A measurement of the amount of fat in the human body, usually expressed as a percentage of total body weight. Most adult males have between 15 and 25 per cent body fat, and most females have 20-30 per cent; values for athletes and others who exercise regularly and vigorously are usually less. Between 4 and 15 per cent of body fat is contained within muscles. This is the most metabolically active and accessible form of fat. It is sensitive to the ‘exercise hormones’ (adrenaline and noradrenaline) and is a very important energy source for ultra endurance activities.

Body fat tends to increase with age, but it is uncertain whether this is an inevitable consequence of the ageing process, or whether it is due to a decrease in daily physical activity.

There are a number of ways of measuring body fat, including the rather macabre cadaver (dead body) dissection analysis; hydrostatic weighing (this involves weighing a person under water and in air); skinfold measurements and the modern techniques of ultrasound analysis; nuclear magnetic resonance; biological impedance; and computerized tomography. One of the easiest ways of determining body fat is by measuring the thickness of the skin at specific points (see skinfold measurements). See also adipose tissue and obesity.

The amount of fat in a human body. It is usually expressed as a percentage of total body weight. An average adult male has about 15-17% body fat: and an average female has about 25% body fat. Athletes, especially those involved in vigorous activities, tend to have low body fat. Body fat can be measured directly by cadaver dissection analysis, but it is usually estimated from body density, for example, by using the Siri equation: percentage body fat = (495/body density) - 450. Other methods of estimating body fat include skinfold measurements, ultrasound, computerized tomography, magnetic resonance imaging, and on special scales using bioelectrical impedance. The absolute body fat is the total weight of fat in the body. It is the product of percentage body fat and total body weight.