It's once again time for New Year's resolutions—the time of year when we solemnly vow to eat right, exercise, save more than we spend, and be nicer to the people around us (at least for a few days). Fortunately, the editors at the Journal of the American Medical Association were nice enough to provide us with a New Year's resolution holiday gift: a newstudy that says it's not so bad to be a bit overweight, as long you're in goodshape.

This study, led by Xuemei Sui of the University of South Carolina, followed 2,600 people over the age of 60 for an average of 12 years. The authors looked at overall fitness (measured by treadmill testing), body mass index (BMI), and other measurements such as waist circumference and body-fat percentage. They then investigated which of these was most important in predicting survival.

What they found struck a blow for common sense—and for the occasional holiday cookie. It was a person's level of fitness, not his or her BMI, that was associated with the lowest mortality over the 12-year study. In fact, people in the lowest 20 percent of physical fitness had more than twice the risk of dying, compared with people who were walking as little as 30 minutes a day, five days a week.

BMI also predicted mortality, but only for people who were severely overweight. And in more good news for the occasionally overindulgent, mortality was about the same for people in the thin and overweight (but not obese) categories.

One of my favorite pieces of advice for patients is to try to be as fit as they can. Studies like this show that even modest steps in this direction can have big payoffs.