Cutting calories through dietary changes seems to promote weight loss more effectively than does exercise and physical activity. But physical activity also is important in weight control.
The key to weight loss is burning more calories than you consume. Because 3,500 calories equals about 1 pound (0.45 kilogram) of fat, you need to burn 3,500 calories more than you take in to lose 1 pound. So if you cut 500 calories from your diet each day, you'd lose about 1 pound a week (500 calories x 7 days = 3,500 calories).
For most people, it's probably too difficult to eliminate the amount of calories through exercise that you could through dieting. That's why cutting calories through dieting is generally more effective for weight loss. But doing both — cutting calories and exercising — can help give you the weight-loss edge. Exercise can help burn off even more calories than just dieting.
Exercise also is important because it can help you maintain your weight loss. Studies show that people who lose weight and keep it off over the long term get regular physical activity. If you lose weight by crash dieting or by drastically restricting yourself to 400 to 800 calories a day, you're more likely to regain weight quickly, often within six months after you stop dieting. Getting regular exercise also can help prevent excess weight gain in the first place.