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Fall 2005

Early Death Risk Due to Obesity Debated

Experts say results of 2005 study may be skewed by faulty methodology

A widely publicized study published in the Journal of the American Medical Association reported that the risk of premature death related to obesity was much less than previously estimated, and that being overweight but not obese does not increase the likelihood of early mortality. Subsequently, many experts have pointed out that the results may have been skewed by faulty methodology. Among other things, the study failed to control for factors such as tobacco use: Smokers are more likely than non-smokers to be thin, and are at greater risk for dying early.

The confusing results also underscore the growing awareness among doctors that body mass index (BMI)—the measure typically used to determine obesity—is not always an accurate indicator. “BMI is simply the proportion of weight to height, which is not a real definition of a person’s body fat,” says Zhaoping Li, M.D., associate professor of medicine and associate chief of clinical nutrition at UCLA.

For most adults, BMI is highly correlated with body fat measures. But for two groups in particular, the correlation is much weaker. At one extreme, highly conditioned athletes might appear to be obese based on their weight levels, but their low body fat levels tell the true story. At the other extreme, many elderly individuals will show normal BMI levels but carry high levels of fat. “As people get older, their body composition can change so their weight is the same as always but their fat percentage rises to the definition of obesity,” Dr. Li explains. “A significant number of people, especially the elderly, lose muscle and become obese, even though they don’t gain weight. It’s most important to eat right and exercise.”

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