Lose body fat without losing muscle by doing heavy weight lifting and being smart about your nutrition. Rapid weight loss methods such as those used by athletes to make weight classes can have many negative effects and increase injury risk. There are a few training and dietary methods that will allow you to avoid this.
A recent review of rapid weight loss methods used by combat sport athletes (judo, tae kwon do, and boxing) who have to “make weight” to compete showed that more than 60 percent of competitive athletes engage in rapid weight loss, losing 5 percent or more body weight in a short period. Methods used are often extreme, including fasting, restricting fat, restricting liquids, using diuretics or laxatives, or vomiting.
Unfortunately, it appears that rapid weight loss strategies can significantly impair cognitive function and mood, but they seem to have less of a negative effect on anaerobic and strength performance. At least three studies suggest that as long as athletes have a chance to rehydrate and re-feed after weigh in, greater weight loss leads to better performance.
Weight reduction is a tricky issue since the immediate ends such as winning appear to justify the means since long-term detriments don’t seem relevant. Reasonable strategies to avoid decreased performance and health problems from weight loss include the following:

1) Gradual weight loss in the range of 1 kg a week is reasonable for athletes, assuming nutrient deficiencies are avoided and adequate protein is consumed. For instance, a recent study showed that when elite athletes involved in heavy weight training reduced energy intake by 500 compared to 1,000 calories a day they were able to completely avoid muscle loss and they improved 1RM squat performance by 12 percent. They also increased jump height by 7 percent. It took them 3 weeks longer to lose the same amount of weight as the 1,000-calorie-reduction group, but their athletic performance improved significantly.

2) Athletes should aim to minimize muscle loss and dehydration when cutting by eating a high-protein diet and getting adequate water and electrolytes.

3) Try taking branched chain amino acids in conjunction with a weight-training program to avoid muscle loss. Creatine supplementation has also been beneficial.

4) Short-term low-carb diets of a few days have led to decreased physical performance, but longer-term low-carb, high-protein diets that allow for metabolic adaptation so that body can efficiently burn fat have produced more positive results.
For example, a study of elite male gymnasts showed that putting them on a very low-carb diet in which they ate 54.8 percent fat, 40.7 percent protein and 4.5 percent carbs for one month with training produced a 2 kg loss of body fat and no decrease in muscle mass. Just as important, the gymnasts performed equally well on strength and power tests before and after the low-carb diet.