Nutrition and exercise are critical for improve body composition. Keeping your calories, fiber and protein in check is a good first step. All exercise can help with fat loss, but weight training is the best way to increase muscle mass. if you start exercising, you may gain two pounds of muscle in the first month. At the same time, you may lose two pounds of fat due to burning more calories through exercise or changes in your diet. Fat mass refers to all the fat tissue in your body. Fat-free mass is everything else, including muscle, organs, bone and fluid.