Consuming fewer calories through dietary changes seems to promote weight loss more effectively than does exercise and physical activity. But physical activity is also important in weight control. The key to weight loss is burning more calories than you consume.
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).
To lose weight by adding exercise alone:
Info collected from the Mayo Clinic at:
http://www.mayoclinic.com/health/weight-loss/MY00432