CHICAGO -- Just a small amount of exercise appears to be enough to keep overweight adults who are not on a diet from gaining more weight.

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A study conducted by researchers at Duke University found that it may take no more than 30 minutes of brisk walking per day to keep from packing on the extra pounds.

According to the study of 120 overweight people, published in Monday's issue of the Archives of Internal Medicine, 73 percent of those who briskly walked 30 minutes a day were able to maintain their weight or even lose a few pounds.

Those who got no exercise during the eight-month study gained an average of almost 2 1/2 pounds.

The researchers said that their study provides the first scientific basis for a "more is better" approach to exercise. People who lost the most weight did the most vigorous exercise -- jogging about 17 miles weekly. They lost an average of nearly eight pounds over eight months. They also shed more than 10 pounds of body fat and gained about three pounds of lean body mass on average.

"Simply put, the more you exercise, the more you benefit," said lead researcher Cris Slentz. "Just as importantly, the control group of participants who performed no exercise gained weight over the period of the trial."

Study Abstract