One pound of fat contains 3,500 calories. Therefore, a negative caloric balance of 500 to 1000 calories per day through dietary changes and increase in physical activity should allow one to lose one to two pounds per week. Any greater weight loss will be extremely hard to continue over a period of time. In addition, restricting calorie intake to less than 1,200 calories a day may cause serious health problems. For adolescents, calorie restriction may impair normal growth.
Aerobic exercise combined with healthful eating helps people lose fat rather than muscle.
Dieting without exercise is seldom successful, because it leads to the loss of muscle mass. Maintaining muscle mass requires more energy than maintaining fat, so losing muscle mass will ultimately slow down weight-loss efforts. The foods you choose should be based on the Dietary Guidelines. People who choose foods they like that comply with the dietary guidelines are more likely to be successful at maintaining a healthy weight. Aerobic exercise should be done at least three days per week for 20 minutes each session at a low to moderate intensity.