CHICAGO -- Overweight adults who are not on a diet need only a small amount of exercise - the equivalent of a half-hour of brisk walking per day - to prevent further weight gain, a study found.
Participants who got no exercise during the eight-month study gained an average of almost 2.5 pounds, according to the study, which was led by Duke University researchers. But 73 percent of those who briskly walked 11 miles a week, or about 30 minutes a day, were able to maintain their weight or even lose a few pounds.
The most noticeable weight loss occurred in those who did the most vigorous exercise - jogging about 17 miles weekly. They lost an average of nearly eight pounds over eight months, and also shed more than 10 pounds of body fat and gained about 3 pounds of lean body mass on average.
The study involved 120 overweight or mildly obese adults who were instructed not to diet during the research. The findings appear in Monday's Archives of Internal Medicine.
The study confirms that exercise without cutting calories is not the most effective way to lose weight, said Dr. Samuel Klein, director of the Center for Human Nutrition at Washington University School of Medicine in St. Louis.
But demonstrating that small amounts of exercise alone can prevent weight gain is significant, given the nation's growing obesity epidemic, Klein said.
"That's important because on average we gain about a pound of fat a year from age 25 to 55 in this country," he said. "Preventing that would be very important."
The men and women studied were ages 40 to 65. They had an average body-mass index of 29.7; anything between 25 and 29 is considered overweight, while 30 and above is obese. The index is a height-weight ratio.
Government estimates suggest more than 60 percent of American adults are overweight.
The study may help settle confusion over conflicting recommendations from the Institute of Medicine and the federal Centers for Disease Control and Prevention.
The institute, a private group that advises the government, has recommended adults get at least an hour of moderate-intensity exercise daily. The study's findings suggest that may be unrealistic and unnecessary for weight maintenance; they are more in line with the CDC's recommendations for a half-hour of moderate exercise per day, said Duke researcher Cris Slentz, the study's lead author.
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