A study published in the Journal of the American Medical Association found that middle-aged women with usual diets who averaged an hour of moderate-intensity exercise per day maintained normal weight (BMI < 25) or gained less than five pounds over a thirteen-year period.
This is pretty discouraging for middle-aged women, says Dr. Whelan. Apparently, exercising twenty or thirty minutes per day is not enough to lose weight, maybe not even maintain it. Many women will find the idea that they need to exercise an hour per day to be unrealistic. I guess the ultimate lesson is that if you want to lose weight, you have to change your eating habits in addition to exercising.