Dear DOCTOR Owen:

I have seen many different ways to measure obesity and find them quite confusing. I used to use the old Metropolitan Life Insurance tables. Most recently, we were using Body Mass Index (BMI), and I have seen the waist-to-hip ratio. There is underwater weighing, and recently I have seen an x-ray device (DEXA) that is supposed to be the most accurate. Which of these tests is the best to predict my risk relative to obesity?

Confused

Dear “Confused”:

Don’t feel like the Lone Ranger, as many physicians are just as confused as you are. Let me quickly summarize the different measurements used and what they mean in practical terms.

• Metropolitan Life Insurance tables, 1959: The standard for measuring “fatness” until approximately 1990. The developers of this measurement system simply took a height and plugged in a weight relative to that height, based on averages in 1959 of body size, and measured the risk of death relative to that body size. For life insurance purposes, this was quite accurate in predicting risk. Quite simply, the heavier an individual relative to his or her height, the greater the risk of death. For scientific purposes, though, this was neither a very good way to define obesity nor to predict risk in trying to make a treatment decision on an individual.
• Percent body fat, either by skinfold measurement or underwater weighing: Commonly used to measure percent body fat, this test involves pinching the skin with a caliper and making estimates of body fat, or measuring the fat directly by seeing how buoyant an individual is in a tub of water. The percent fat predicts the amount of risk. Though both tests are comparable in accuracy, they still do not predict the risk of cardiovascular outcome relative to fatness very precisely. Some individuals, who are genetically fat all over, do not have a high risk of cardiovascular disease. Therefore, for medical treatment decisions or scientific studies, the tests still lack predictive value.
• Body Mass Index (BMI): This is a mathematical formula, which measures the height and weight of an individual, and calculates for size of the individual frame indirectly. The BMI is an attempt to get around the large-frame issue and make everyone fairly standardized. It is very accurate in predicting risk of cardiovascular diseases, and is now the standard used by the Centers for Disease Control. Anyone with a BMI of 25 is considered in the high-risk category and should seek fatness intervention. To calculate your BMI, click on the drdiet.com Web site. While more accurate than the tests outlined above, it still tends to “lump” large groups of people together and, therefore, loses some accuracy.
• DEXA x-ray: While certainly the most accurate test on the market, the DEXA measures every gram of fat in the body and can isolate fat to a particular region, such as the trunk. It is expensive and takes considerable technical skill to administer. The DEXA is the most accurate method for measuring body fat and risk, but is used more for scientific research purposes than for the general public.
• Waist-to-hip ratio: Now considered the most accurate and easiest measure of risk of death from cardiovascular disease. The small-legged/big-bellied person, male or female, is at high risk for diabetes, hypertension, high cholesterol, and cardiovascular diseases. The weight, called visceral fat, tends to accumulate, literally, in the belly—around the organs. Some women with thin arms and legs, as well as big potbellies, are also at high risk. The test is simple. First, measure (using a tape measure) around your stomach at approximately the naval or the widest margin; next, measure around your hips at the level of the buttocks. If your stomach is 1.5 times larger, you are at risk.

These measurements are compared and a good review of the subject appears in Obesity Research, Vol. 7, No. 3. I hope this clears up some of the confusion. The bottom line is, the leaner you are the healthier you are, especially non-smokers.