Commentary: Recent research suggests...

By IAIN MURRAY, Special to UPI  |  June 27, 2002 at 6:16 PM
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WASHINGTON, June 27 (UPI) -- "Globesity" is the public health issue of the moment. Southwest Airlines has said it will now charge two fares for obese passengers. Ted Kennedy has held Senate hearings on the issue. The World Health Organization is so worried by the fact that, according to its calculations, 22 million children worldwide are overweight or obese that it has advocated taxes and marketing restrictions on sugary food and drink. There is a widespread perception that Americans are too fat, and this is backed up by the official statistics.

But there's a problem. Under federal body mass standards adopted in 1998, Tom Cruise is now probably obese. So is Russell Crowe. Even Michael Jordan is overweight. The guidelines, from the National Heart, Lung and Blood Institute, moved 29 million Americans who had previously been defined as healthy into a category that doctors should regard as being at risk because of their weight. Even more alarmingly, 61 percent of Americans are now categorized as overweight and 26 percent as obese. The trouble is that the scientific debate on this issue is far from settled.

The standards rely on something called the Body Mass Index, BMI, which is derived by dividing weight in kilograms by the square of the height in meters, thus getting a good indicator of weight adjusted for height. Researchers generally agree that a BMI up to 24 is an indicator of little or no risk to health. A BMI of 27 or above is linked to higher risk of heart disease, diabetes, stroke and other weight-related problems. The risks increase especially when the BMI is greater than 30. The problem is what to do with the band whose BMI is 24 to 27. The National Center for Health Statistics has only ever classified those with a BMI of 27 or above as "overweight," but the new standards start that category at a BMI of 25, well below the level clearly associated with health risks.

This categorization is controversial. "I'd rather see a caution zone from 25 to 26.9, where you tell people, 'Don't gain more weight, become physically active,'" Judith Stern, professor of Nutrition at the University of California, Davis, told Newsweek in 1998. She went on, "There's no evidence that BMIs lower than 27 are associated with significant increases in mortality."

Moreover, there are weaknesses in the science behind the BMI. It does not distinguish between fat mass and lean mass. That's how Michael Jordan can be classified as overweight. Most body-builders, without an ounce of fat on their bodies, will also count as overweight. This is because BMI derives its authority from the traditional method of assessing risk associated with weight, which has been to look at how mortality corresponds with weight. This is problematic, as many causes of death also cause people to lose weight. Smoking is a prime example, as smokers tend to weigh less but die earlier than non-smokers. On the other hand, alcoholism often leads to weight gain, which might be incidental to the death of the alcoholic.

Another important issue in the development of healthy weight standards is race. The standards have been developed from predominantly white populations, and may not be appropriate for other groups. In Hong Kong, for instance, a very small proportion of the populace is obese -- only 6 percent has a BMI of 30 of higher -- but incidences of diabetes, hypertension and other metabolic complaints are much higher, indicating that for Asians, perhaps the BMI standards are inappropriate.

But it is those athletic film stars and glamorous athletes who sum up the greatest problem with the BMI. It is perfectly possible to be healthy, attractive and "overweight." Waist circumference is perhaps the best way to tell whether someone is overweight and unhealthy (fat is stored primarily at the waist). Some physicians do correct for waist circumference. Michael Jordan's BMI under this system falls to 21. Shaquille O'Neill, however, who has only 5 percent body fat, despite his much-publicized consumption of burgers, still comes out as overweight.

The simple lesson is that BMI is a useful tool, but it doesn't tell you everything about an individual. As for whether America is worryingly overweight, we do not know how many of the 35 percent of adult Americans who the government now classes as overweight are actually in Stern's "caution zone," but we do know that 26 percent -- well over 50 million people -- have a BMI of 30 or greater. That is well into the "danger zone."

It is interesting, however, that Americans don't view this as a public health problem. In a recent survey by Harvard and Princeton researchers, 65 percent blamed individuals for lacking the willpower to diet and exercise. They may have a point. Studies carried out at Dallas' Cooper Institute seem to indicate that even moderately active overweight people have far lower death rates than sedentary people of the same weight. Even one half-hour walk per day takes overweight people out of the risk categories. The will to exercise, it seems, may be a more important factor in determining health than a simple measure of weight.

(Iain Murray is director of research at STATS -- the Statistical Assessment Service, a Washington-based non-profit, non-partisan public policy organization dedicated to analyzing social, scientific and statistical research. This column examines the facts behind recent statistical studies that have made the news but been misinterpreted, failed to make the news for some reason or are just plain weird.)

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