Too Fat? First, Get off the Couch

There's been a lot of debate over the past several years about whether you can be both fit and fat. That is, can you be overweight but as healthy as a lean person if you exercise regularly? A study released today in the Archives of Internal Medicine suggests that at least as far as heart disease in women goes, body weight and exercise are both important variables.

The discussion is complicated by the fact that the body mass index, the number researchers typically use to gauge overweight and obesity, is not always a perfect measure of body fatness. On one hand, because it simply relates weight to height, it may put musclebound but lean athletes into the "overweight" category. (Here's a study looking at its use in college athletes and nonathletes.) And as I wrote earlier this month, a low BMI may give some thin people a false sense of security, even though their percentage of body fat is high.

Studies looking at the relationship between health and exercise and body weight are often confusing. One, published in December in the Journal of the American Medical Association, found that among people 60 and older, fitness was the better predictor of longevity than BMI. And the study released today says that yes, exercise absolutely makes a difference in the risk of heart disease among the overweight and obese. But so does weight. Compared with women of normal weight (a BMI less than 25) who were active (or burned off at least 1,000 calories a week), inactive overweight women had an 88 percent higher chance of developing heart disease; active overweight women had a 54 percent higher risk. In women who were obese, the active group had an 87 percent higher chance of getting the disease, while the inactive obese women were at highest risk: Their odds of getting heart disease were more than 2½ times as high as those for the lean active women.

The lean women, even the inactive ones, still had far lower odds of later developing heart disease than the overweight women, including those who were exercising. "The physical activity did make a significant difference and reduced the risk of heart disease. But according to our study, to fully reverse the risk of heart disease from being overweight or obese, you'd also have to lose weight," says Amy Weinstein, an instructor of medicine at Harvard Medical School and an author of the study.

Most nutritionists would say that rather than being obsessed with the scale or your BMI, you should get regular exercise (the more the better, according to this latest study) and eat healthfully. If you do that, with an eye to portion control, you're likely to settle into a healthy, maintainable weight range. For more on how to eat well, check out this story about dietary patterns. And for help in overcoming excuses we all use not to exercise, try this piece.