For every pound you lose, your resting metabolism drops by about 2 to 10 calories a day. Lose 10 pounds, and you now have to eat 20 to 100 fewer calories to maintain your trimmer physique, not factoring in exercise. However, you can prevent your metabolic rate from slipping while you get slim. One way is to lose fat but maintain muscle. You can do this by reducing calories and increasing aerobic and resistance exercise, says Hickey. Crash diets (fewer than 1,000 calories a day) may result in a higher percentage of muscle loss.
Tip Lose weight by cutting 250 calories a day and burning 250 calories per day through exercise. That will help you retain or even gain muscle while you lose a greater percentage of body fat.
Source: Prevention Magazine