Losing weight vs staying off it

Losing weight is difficult, and keeping it off may be even harder. So Harvard researchers set out to determine exactly how much physical activity women need in midlife to avoid gaining weight as they age.

The researchers found that one hour of moderate activity a day, including recreational activities such as brisk walking, leisurely bicycling, ballroom dancing and playing with children, prevented women of normal weight from gaining more than five pounds over any three-year period. Half that amount of vigorous activity, like running, jogging or fast biking, will do the trick as well, they said.

Women who got the same amount of exercise but were heavier to start with were not able to avoid gaining weight, however. Neither were women of normal weight who got less than seven hours a week of moderate activity, according to the study, published in the March 24 issue of The Journal of the American Medical Association.

The average weight gain over the course of the 15-year study, which followed 34,079 healthy women with an average age of 54 at the beginning, was just over five pounds. The researchers did not take diet into account.

"It's so hard to lose weight and maintain the loss, so whatever weight you are, you should try to stay that weight. That is a success," said the paper's lead author, Dr I-Min Lee, an associate professor of epidemiology at Harvard School of Public Health.