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How fat are you?

Joan Conway and her colleagues are pioneering a new method for measuring total body fat. They shine near-infrared light on the skin at selected body sites, and then, using a spectrophotometer, measure the degree to which that light is absorbed or modified b irradiated tissue within 1 or 2 centimeters of the skin surface. Since fat, water and protein each absorb most efficiently different spectral frequencies, one can focus on fat's peak interacting wavelengths to gauge total body fat, explains Conway.

These "infrared interactance" measurements are made at 1-nanometer intervals between about 750 and 1,100 nm. It takes less than a minute to scan the range of frequencies at each body site, using a 2-centimeter-diameter fiber-optic cable, which also transmits the tissue-altered frequencies back for analysis. Although Conway now averages readings from five sites to calculate total body fat, her data--based on a survey of more than 200 peope aged 19 to 65--show these five-site averages to be virtually identical to biceps-fat readings alone.

Conway says her data show the technique is more accurate than the commonly used calipered measurement of pinched skin folds, and is more reliable than the electrical-impedence technique (which, because it measures the body's electrical conductivity, can be affected by such factors as blood flow, body water content and body sales content). In fact, Conway's studies show that her technique gives fat calculations within 3 percent of the best techniques--deuterium oxide dilution and underwater weighing. Moreover, where deuterium oxide dilution requires drawing blood and underwater weighing requires immersion in a calibrated pool, the infrared technique can be completed in three minutes and may ultimately require no more than the rolling up of one's sleeve.

Conway's system, the only one of its kind in existence, now sprawls across a desktop. But she expects that within tow or three years a commercial version, perhaps only the size of a thick paperback book, could be available.
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Title Annotation:new method for measuring total body fat
Author:Raloff, Janet
Publication:Science News
Date:Nov 30, 1985
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