Adults need at least 250 minutes per week -- equal to 50 minutes of exercise five days a week -- to lose significant weight, according to the latest recommendations from the American College of Sports Medicine (ACSM).
If you are trying to maintain your weight rather than lose, you may still be OK with the 30-minute workouts. The ACSM recommends that adults participate in at least 150 minutes per week of moderate-intensity physical activity to prevent significant weight gain. Overweight and obese adults, however, are more likely to reach their goals with at least 250 minutes. The report also recommends strength training as part of the exercise regimen, in order to increase fat-free mass and further reduce health risks.