Machine measures of fat mass and fat distribution

MACHINE MEASURES OF FAT MASS AND FAT DISTRIBUTION
Technological developments in the area have led to a number of different machines now being available for directly or indirectly measuring body fatness. Some of these are extremely expensive and would not be used in the normal day-to-day counseling situation. Others are now becoming more portable and more accessible and provide at least an opportunity for adding to other measures. The current range of machines include: underwater weighing, bio-impedance analysis, near infrared analysis, etc.
Near infrared analysis (NIR). NIR is a technique developed for the US Food, Drug and Agriculture Apartment (FDA) to measure fat content of beef carcases. It is based on the principles of light absorption and reflection using near infrared spectroscopy.
A small, hand-held probe, which emits electromagnetic radiation through a central bundle of optic fibres is placed on the skin at a selected site (usually the biceps for overall fat measurement). Optic fibres on the edge of the same probe absorb the energy reflected back from the tissues and this is then passed on to a spectrometer for measurement. Because muscle tissue is denser than fat, muscle and fat can be determined by the end of the light spectrum reflected back to the machine through several centimetres of tissue. When multiple sites are used, the measure is quite valid. MR machines using only one site, (i.e. the biceps) are now commercially available and reasonably portable (there is even one hand-held device) and within the cost range of someone working in counselling. They require one simple measure which takes about 20 seconds, plus some other information fed into the computer on age, sex, fitness level etc. The whole measurement process takes only 1-2 minutes.
Again, the estimation of body fat is based on algorithms built into the computer and hence the estimates are only as good as the algorithms that support them. In general NTR has been found to be slightly less valid than BIA measures, but reliability is unclear. The sensitivity of the measure is unknown. Used by a skilful operator it can be an effective motivational tool and can be used to measure relative changes in body fat in different body locations, i.e. total and regional fat assessment.

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