Another method of evaluating a person’s weight is estimating the percentage of body fat. Obese is defined as 32 percent or higher for women and 25 percent or higher for men. The amount of body fat a person has is nearly impossible to measure directly; many tests have been developed to estimate it. Many of these methods estimate body fat percentage by evaluating the density of a person’s body by submerging him or her in water. Since fat is less dense then muscle and bone, formulas can be used that incorporate how much water a person has displaced to estimate his or her body fat percentage.
An easier, yet probably less accurate, way to estimate body fat percentage is a skin-fold test: Calipers measure the thickness of fat on various areas of the body. The calipers, which resemble tongs, are used to pinch typically fatty areas such as the stomach, thigh, or back of the upper arm. The measurements are then plugged into a formula to convert the thickness of these fat folds into a percentage of body fat. The numbers can fluctuate, however, depending on the type of calipers used, the consistency of the measurer, the distribution of body fat of the person being measured, and the formula used. The estimate is also dependent on the measurer testing in a precise location and using a fixed pressure. A measurer who presses too hard would increase the amount of fat measured and overestimate the fat percentage. The number of measurements taken can also affect the body fat estimate. Some formulas rely on seven measurements from the body, whereas other formulas only require three measurements. If a person is measured on the part of the body that is more fatty than other areas that are not measured, that individual’s fat percentage could be overestimated. At best, these percentages might be used to measure the change in one person over a period of time if the same measurer and same areas of the body are used. As with all calculations used to determine the appropriateness of one’s weight, the numbers do not take into account the variations in body type.
Source: "Drugs The Straight Facts: Weight-Loss Drugs," Chelsea House, 2009
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