NEW YORK (Reuters Health) - Greater amounts of physical activity than currently recommended may be necessary to prevent people from gaining weigh, and to help them lose weight and keep it off, according to updated guidelines issued by the American College of Sports Medicine (ACSM).

"In the midst of a genuine crisis in Americans' health related to what we eat and how little we move, these guidelines are meant to provide an understanding and clarification of the role of physical activity and its relationship to weight," Dr. Joseph E. Donnelly of the University of Kansas in Lawrence and chair of the advisory committee noted in a statement.

"Now that we have the latest information on how much physical activity is part of the equation, we can continue the educational process to help people who struggle with their weight," Donnelly added.

In a 2001 position paper, the ACSM recommended a minimum of 150 minutes per week (roughly 30 minutes per day 5 times per week) of moderate-intensity physical activity for overweight and obese adults to improve health; however, 200 to 300 minutes per week was recommended for long-term weight loss.

"More recent evidence has supported this recommendation and has indicated that more physical activity may be necessary to prevent weight regain after weight loss," reads the ACSM's position paper published in the latest issue of the College's journal Medicine & Science in Sports & Exercise.

Specifically, evidence published after 1999 indicates that between 150 and 250 minutes per week of moderate intensity physical activity is effective in preventing weight gain greater than 3% in most adults but will provide "only modest" weight loss.

Greater amounts of weekly physical activity -- in the order of 250 minutes or more per week -- have been associated with "significant" weight loss, the ACSM notes. Overweight and obese adults will most likely lose more weight and keep it off with at least 250 minutes per week of exercise.

The ACSM also recommends strength training as part of a health and fitness regimen. "Resistance training does not enhance weight loss but may increase fat-free mass and increase loss of fat mass and is associated with reductions in health risk," the writing committee notes.

Dieting combined with increased physical activity will increase weight loss as compared to dieting alone.

SOURCE: Medicine & Science in Sports & Exercise, February 2009.

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