To reduce body fat and stay at the same weight, you would need to build muscle at the same time as you lose fat, which isn't possible for most people. Bodybuilders often bulk up to build muscle, then slim down to lose extra body fat, which is an easier, more effective way to go about this than trying to do both at the same time. The end result is that you weigh the same as before but you have more muscle, less body fat and you look leaner.
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Eat the Right Number of Calories
To maintain your current body weight, a woman typically needs between 12 and 13 calories per pound of body weight if she doesn't exercise; between 14 and 15 calories per pound if she's moderately active and about 16 calories if she's very active. Men usually need between 14 and 18 calories per pound, depending on their activity level.
Each pound consists of about 3,500 calories, and you can only gain about half a pound of muscle per week, so you'll need to eat an extra 250 to 500 calories per day while trying to gain weight in the form of muscle. It's most likely you'll also gain some fat in the process, however. Once you've built up your muscle and are ready to lose fat, you then go on a reduced-calorie diet, cutting 500 to 1,000 calories per day to lose weight at a healthy rate of 1 to 2 pounds per week, while continuing to exercise to lose fat so you can return to your previous weight.
Get Plenty of Protein
Eating plenty of protein is necessary when you're trying to gain muscle and also trying to lose fat. Between 10 and 35 percent of the calories you eat should come from protein, but don't eat more protein than this, as it can be risky. On a 2,000-calorie diet, this means eating 50 to 175 grams of protein per day. Eating something containing protein about 15 minutes before and within an hour after a resistance training workout may help improve muscle gains. Focus on lean protein, such as eggs, legumes, low-fat dairy products, fish and poultry, to avoid consuming large quantities of unhealthy saturated fat.
During weight loss, higher protein consumption helps limit muscle loss and maximize fat loss. A study published in the Journal of the American Dietetic Association in 2008 noted that people who followed a diet that was higher in protein lost less muscle during weight loss than those who followed a low-protein diet.
Regardless of whether you're trying to build muscle or lose fat, you also need carbohydrates and fat, which provide fuel for your muscles and workouts. Between 20 and 35 percent of your calories should come from healthy unsaturated fats and the rest of your calories should be from high-quality carbohydrates such as fruits, vegetables and whole grains.
Cardio to Reduce Body Fat
Although you don't want to do too much cardio when you're trying to gain weight in the form of muscle, you'll get better fat loss results if you increase your cardio when trying to lose weight. Cardio is important for burning fat. If you're short on time for cardio workouts, you may want to give high-intensity interval training a try. This involves short, 30- to 60-second bursts of high-intensity exercise -- during which it is impossible to talk -- followed by longer intervals or about two minutes, of moderate intensity exercise. Repeat these intervals eight to 10 times, depending on your fitness level. This type of workout helps reduce fat and helps increase fitness in a shorter time than a workout with a steadier intensity level. To burn fat, you should aim for about 30 minutes per day of high-intensity exercise or about 60 minutes per day of moderate-intensity exercise, but you shouldn't do these HIIT workouts more than once or twice per week or you could increase your risk for injury -- and you should only do them periodically -- not as a regular workout throughout the year, according to the American Council on Exercise.
Resistance Training for Muscle Building
Resistance training is important when trying to build muscle and lose fat. The older you get, the harder it is to maintain the muscle you have and also to build more, so regular resistance training is essential. This means at least two resistance training sessions that focus on all major muscle groups per week on non-consecutive days, because your muscles need time to heal between workouts. Include exercises that work the hips, legs, arms, shoulders, chest, back and abdominal muscles. If you're going to work out on two consecutive days, work different muscles each day, to minimize the risk of injury.
The right mix of diet and exercise will help you lose more fat and less muscle as you lose weight. Any weight lost through dieting will consist of about 25 percent muscle if you don't do resistance training workouts. A study published in Diabetes Care in 2010 noted that a combination of resistance training and a high-protein diet during weight loss can help improve body composition and weight loss better than a lower-protein diet, with or without resistance training.