Is it okay to be fat if you’re fit?

(This article was first printed in the March 2005 issue of the Harvard Health Letter. For more information or to order, please go to www.health.harvard.edu/health.)

Research suggests that physical activity may cancel out some of the bad effects of being overweight or obese.

Humanity is getting pudgy, and worse. High-calorie diets and low-activity lifestyles have created a massive “globesity” problem. About 300 million people around the world are now obese (a body mass index [BMI] of 30 or more).

One person who saw it coming was Ancel Keys, a pioneering epidemiologist and early champion of the Mediterranean diet who died in late 2004 at age 100. A 2004 editorial in the New England Journal of Medicine opened with this 1949 quote from Keys: “While our calorie intake goes up, our output goes down. The wonderful advances of technology not merely free us from back-breaking toil; they make it almost impossible to get a decent amount of calorie-using exercise.”

The typical response to gaining pounds is to try to lose them, usually by dieting. But what if we were to accept some tubbiness as a consequence of our cushy 21st-century lifestyles and instead figure out ways to offset its bad effects? Several studies have suggested that exercise might be just the thing.

Heavy but healthy

Physical activity “cools off” inflammatory processes and helps our bodies keep insulin and blood sugar at healthy levels. Extra weight, especially when it’s concentrated in a pot belly, stirs up inflammatory processes and disrupts blood sugar regulation. So it makes sense that exercise might significantly blunt obesity’s ill effects even if it doesn’t cause weight loss.

Moreover, research shows that it’s possible to be heavy and fit, cardiovascularly speaking. In various studies, a sizable percentage of people who are overweight — particularly in the moderate range (a BMI between 25 and 30) — do well on treadmill tests and are fairly physically active, judging by their answers to questionnaires.

The studies seesaw

The first major fatness versus fitness study was conducted by researchers at the Cooper Institute, a nonprofit organization in Dallas that promotes fitness. In a study of 22,000 men, ages 30–83, the researchers measured subjects’ body composition (the proportion of fat to muscle) and put them through treadmill tests. During eight years of follow-up, 428 of the men died. Men who were overweight but fit (as measured by a treadmill test) were two times less likely to have died than men who were lean but not fit. Moreover, the all-cause mortality rate of fit, overweight men wasn’t significantly different from that of the fit, lean men. Their heretical conclusion: If you’re fit, being overweight doesn’t increase mortality risk.

A study in the Journal of the American Medical Association (JAMA) in September 2004 came to a similar conclusion. For almost four years, the researchers tracked heart attacks and other “cardiovascular events” among 900 American women who had had a coronary angiogram. They found that lack of physical activity, as calculated from answers to standard questionnaires, was a better predictor of an adverse event than weight.

A few months after the JAMA study, Harvard researchers — including Health Letter board members Drs. Walter Willett and JoAnn Manson — weighed in with a study of their own. Writing in the New England Journal of Medicine, they analyzed weight, physical activity, and mortality data culled from the Nurses’ Health Study over a 20-year period.

Both sides in the fitness vs. fatness debate could take some comfort in the results. Physical activity lowered the death rate across all weight categories — lean (BMI under 25), overweight (BMI 25–29.9), and obese (BMI 30 or over). And nurses in the mid-range overweight category who were physically active (as little as one hour a week counted) had a lower risk of death than lean nurses who were inactive (exercising less than an hour per week). Being a little active and a little fat wasn’t such a bad combination.

But physical activity didn’t completely eliminate the risks that attended being overweight or obese. In fact, when the nurses were grouped by how active they were, the heavier nurses were more likely to have died than the lighter ones at every activity level.

Here’s the real bad news: Even putting on a medium amount of weight (9–20 pounds) during adulthood was associated with a higher risk of death.

The battle of the bulge: A two-front war

Despite the differences in these studies, they all suggest that physical activity will offset some of the effects of excess weight, if it’s just a few extra pounds. So apart from any weight-loss goals you’ve set for yourself, it’s important to exercise regularly. Yet exercise isn’t going to magically erase all the health risks of being heavy. If you are lean, it’s worth the effort to stay that way. And if you’re heavy, it’s a good idea to hop on the scale and, yes, try to lose some of that weight, particularly around the waist.

Ancel Keys recognized over 50 years ago that the modern waistline will expand because of our sedentary lives. Besides, as a JAMA editorial pointed out, there really isn’t much choice between losing weight and exercise. Exercise is really the only way to improve fitness. But it’s also an essential feature of successful weight-loss programs. If you want to lose weight and keep it off, you have to exercise anyway.

(This article was first printed in the March 2005 issue of the Harvard Health Letter. For more information or to order, please go to www.health.harvard.edu/health.)

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