NEW YORK (Reuters Health) – Results of a study show that overweight women who want to lose weight and keep it off should try to get at least 275 minutes of exercise a week, or about 55 minutes a day for 5 days a week, in addition to limiting calories.

Dr. John M. Jakicic of the University of Pittsburgh and colleagues say their research “would suggest that the level of physical activity that may be necessary to sustain weight loss for as long as 24 months is approximately twice the public health recommendation for physical activity.”

The minimum amount of weekly exercise recommended under current public health guidelines is 150 minutes, but more and more experts believe that people need to spend more time being physically active in order to sustain weight loss long-term, Jakicic and his team note in the latest issue of the Archives of Internal Medicine.

To better understand how much exercise overweight women really need to maintain a healthy weight, the researchers randomized 201 overweight and obese women to four different exercise intensity groups: burning 1,000 calories weekly in moderate exercise; burning 1,000 calories a week by exercising vigorously; burning 2,000 calories with moderate exercise; or burning 2,000 calories with vigorous exercise.

Study participants cut their calorie intake to 1,200 or 1,500 daily depending on their weight at the beginning of the study. They also attended group meetings and received periodic phone calls from intervention team members.

At 6 months, the women in the study had lost an average of 8 percent to 10 percent of their body weight, and there was no difference in the amount of weight loss among the four exercise intensity groups. At 24 months, average weight loss was 5 percent, again with no difference among the groups.

But when the researchers looked at the women who had lost 10 percent or more of their body weight and kept it off, they found that their average physical activity level at both 6 and 24 months was 1,800 calories. This is equal to about 254 minutes of exercise each week, or 55 minutes a day for 5 days a week.

These women also completed more of the follow-up calls with the intervention team (81.5 percent vs. less than 69 percent for women who kept off 5 percent of their weight or less), ate less fat, and scored higher on a standard test of healthy eating behaviors.

“This study demonstrates the difficulty in sustaining weight loss of 10 percent or more of initial body weight,” as well as the difficulty of keeping up a high level of physical activity long-term, the researchers say. Staying in touch with the intervention team and healthier eating habits may also have been important factors in weight loss success, they conclude.

SOURCE: Archives of Internal Medicine, July 28, 2008.