Health Checkup: Women and Health

Calories in, calories out. It's a simple rule, and for the weight-conscious, it means one thing: the more you eat, the more you have to burn.

But how much does it take to keep you trim?

According to a study published in March in the Journal of the American Medical Association, middle-aged women who aren't counting calories need an hour of moderate physical activity per day to maintain a healthy weight — surprising since that's nearly three times the 150 minutes per week currently recommended by the Department of Health and Human Services.

The study followed more than 34,000 healthy women for up to 13 years and tracked their weekly activity. In general, for women who began with a normal range body mass index (BMI), 60 minutes per day of exercise like hiking was enough to maintain a healthy weight. For women who were already overweight, however, exercise alone was not sufficient to lower BMI. The findings emphasize the importance of obesity prevention: once you put the weight on, it's hard to take it off.