MEASUREMENTS AND ASSESSMENT OF FATNESS

Summary of main points.

• Accurate measurements of body fat, mass and distribution require a variety of techniques and there is no one entirely satisfactory measure.

• A combination of measures is usually necessary to determine health risk.

• Validity, reliability and sensitivity of measures are an important indication of their worth.

• BMI is a good measure of body mass; waist circumference of fat distribution; skinfolds are useful measurements in the hands of experienced operators and with thon severely obese.

• New measures of central fat, such as abdominal diameter, may have important uses in the future.

Typically, the most commonly used measure of body fatness has been body weight. This is then compared with a table of ‘ideal weights’ prepared by life insurance companies on the basis of actuarial data, relating weight to the risk of an early death or to average weights in the population, and some measure of overweight calculated on the basis of population figures.

The advantage of weight is that it is a simple, accurate and reliable measurement. For individuals, significant changes in weight over the long term usually reflect significant changes in body composition. However, weight is often not a true reflection of obesity—particularly in those in the population (e.g. athletic males) who might have high body density due to muscular structure—nor a good indication of health risk, because measures of weight (in contrast to body fat distribution) do not correlate highly with illness risk. Height is, of course, a confounding factor and hence the calculation of body mass index, or BMI, which corrects for height, has become the norm.

More recently, it has been realised that BMI is also not always a good representation of fatness, again because of the bias against those with a high body density (i.e. those with a high fat free mass to fat mass ratio, FFM:FM). Hence there has been a recent move towards new measures of total body fat and fat distribution, including the better use of simple anthropometric measures such as height, weight and circumference measures. There has also been a move to develop cost-effective machines which accurately measure fat, in contrast to body mass.

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