How Much of You Is Fat

During your evaluation, your tester will probably weigh you. Just know that your weight is of limited value. When you hop on a scale, you learn the grand total weight of your bones, organs, blood, fat, muscle, and other tissues. This number can be misleading because muscle weighs more per square inch than fat.

Consider two men who stand 5'8" and weigh 190 pounds. One guy may be a lean bodybuilder who has a lot of muscle packed onto his frame. Another guy may be a couch potato whose gut hangs 4 inches over his belt buckle. Even a low weight doesn’t necessarily indicate good health or fitness. It may simply mean that you have small bones and little muscle.

More helpful than your body weight is your body composition — how much of your body is composed of fat and how much is composed of everything else. Your body composition is also called your body-fat percentage. If you score a 25 percent on a fat test, this means that 25 percent of your weight is composed of fat.

Like your weight, your body-fat percentage is not necessarily a measure of your health. True, cardiovascular disease, diabetes, and certain cancers are more prevalent among overweight people — men who have more than about 20 percent body fat and women who have more than about 30 percent body fat. However, some researchers believe that these health problems are not caused by the extra fat itself but rather by a lack of exercise and a poor diet. In other words, if you exercise regularly and eat well, extra body fat may not compromise your health. So consider your body-fat score in a context with other health measures, such as your cholesterol levels, blood pressure, and other gauges of fitness, such as a submaximal test and your resting heart rate. An additional number to consider is the circumference of your waist. Excess abdominal fat — the type that lies deep in your belly, clumped around your organs — is linked to increased risk for heart disease. Heavy thighs, on the other hand, do not appear to be related to health problems. (In other words — to use terms we can all relate to — a beer belly is more harmful to your health than saddlebags.) Men with waist measurements greater than 40 and women with waist measurements greater than 35 should consult a physician. Although body fat testing has its limits, your results can give you great insight into how your fat-loss and exercise program is coming along. Sure, your scale can tell you that you lost 7 pounds. But a body-fat test can tell you that your 7-pound loss means that you lost 10 pounds of fat and gained 3 pounds of muscle, results that are probably more motivating.

Body-fat testing also can tell you if you have too little fat. Maybe you can never be too rich, but you definitely can be too thin. For women, super-low body fat — below about 16 percent — may lead to problems such as irregular menstrual periods, permanent bone loss, and a high rate of bone fractures. Keep in mind that every body-fat testing method has room for error. At a recent fitness convention, Suzanne had her body fat measured by two different methods — and appeared to have gained 11 percent body fat in a matter of 15 minutes. You may even get wildly different readings using the same test, depending on the skill of the tester or the condition of the equipment. The only way to measure body fat with complete accuracy is to burn yourself up and take a carbon count of the ashes. Because that technique doesn’t draw too many volunteers, scientists have developed a number of other methods. Here’s a look at the ones you’re most likely to come across.