WASHINGTON - When it comes to living longer, fitness may trump fatness, U.S. researchers said.

Men and women who were fit, as judged by a treadmill test, but were overweight or obese had a lower mortality risk than those of normal weight but low fitness levels, the study in the Journal of the American Medical Association showed.

Exercise expert Steven Blair of the University of South Carolina and colleagues tracked about 2,600 people age 60 and up, examining how physical fitness and body fat affected their death rates over 12 years.

Those in the lowest fifth in terms of fitness had a death rate four times higher than participants ranked in the top fifth for fitness.

"Being fit provides protection against mortality in these men and women 60 and older, whether they're normal weight, overweight or obese," Blair said in a telephone interview.

The findings are particularly relevant as people in the United States and many other countries live increasingly sedentary lifestyles and obesity rates remain high. At the same time, the populations are aging in many nations.

"I believe we have an obesity epidemic. It's a bad sign. We should not ignore obesity," Blair said. "But what happens all too often is we focus nearly exclusively on obesity and forget the activity and fitness part."

MODEST EFFORT HELPS

The researchers assessed the fitness of the participants using a treadmill test, seeing how long they could walk while the treadmill's incline increased. They measured body mass index -- calculated from a person's weight and height -- as well as waist circumference and body fat percentage.

The study showed that even a modest effort to improve physical activity can provide health benefits, the researchers said. Those in the bottom fifth in terms of fitness were about twice as likely to die than those in the next fifth.

"You shouldn't be scared and think, 'Oh, I'm overweight, I'm obese, it's useless for me to be physically active,'" Dr. Xuemei Sui, another University of South Carolina researcher who worked on the study, said in a telephone interview.

Drastic steps may not be needed, the researchers said.

"If you're overweight or obese and you're sedentary and unfit and you start taking three 10-minute walks a day and you do that at least five days a week, you're not going to lose an enormous amount of weight," Blair said.

"You're going to still be heavy. But you're going to be much healthier if you do that," Blair said.

Blair also stressed the importance of a healthful diet including lots of fruit, vegetables and whole grains.

More than a third of U.S. adults are obese, according to the U.S. Centers for Disease Control and Prevention. Obesity is a major risk factor for cardiovascular disease, certain types of cancer and the most common form of diabetes, the CDC said.

The CDC also has found that more than half of adults do not engage in regular physical exercise. Exercise cuts the chances of dying of coronary heart disease, as well as lowering the risk for stroke, colon cancer, diabetes and high blood pressure, the CDC said.

(Editing by Maggie Fox and Eric Walsh)