Exercise guidelines for adults differ among health organizations, depending on whether they emphasize overall health, weight loss or weight maintenance. American College of Sports Medicine: Moderate activity 150 to 250 minutes a week to prevent weight gain. Institute of Medicine: 60 minutes a day to prevent becoming overweight. Department of Health and Human Services: At least 150 minutes a week for health benefits. American Heart Assn.: At least 30 minutes a day, five days a week, of moderate activity or 20 minutes a day, three days a week, of vigorous activity to maintain health. Brigham and Women’s Hospital study: 60 minutes a day for normal-weight women to maintain weight.