Cutting calories appears to promote weight loss more effectively than does increasing exercise.
The key to weight loss is to consume fewer calories than you burn. For most people, it's possible to lower calorie intake to a greater degree than it is to burn more calories through increased exercise.
That's the reason cutting calories through dietary changes is generally more effective for weight loss. But doing both — cutting calories through diet and burning calories through exercise — can help give you the weight-loss edge.
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.
Exercise 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.