Common sense tells us a pound of muscle and a pound of fat have to weigh the same, but they do differ in density. This means if you look at five pounds of muscle and five pounds of fat side by side, the fat takes up more volume, or space, than the muscle. That’s important when you’re on a diet and part of your goal is the lean look of muscle, not the flabby look of fat.

Quick Summary of Fat Fat can not become muscle and muscle can not become fat. Fat can only be reduced if the number of calories expended in a day exceeds the number of calories consumed in a day. Fat will be gained if the opposite occurs. If you stop training, but compensate for this with a slight reduction in diet, your body fat will not increase. If you begin training but also increase your dietary intake, you can gain fat. Fat cells act as one, meaning you can not choose where you lose it or gain it.   Quick Summary of Muscle Changes in muscle size, density and/or efficiency cause an increase in strength; however, these changes only result if the muscle is stimulated beyond what it is accustomed to. Weight training is the easiest way to control and monitor the changes in your muscle physiology. By manipulating your sets, reps and weight lifted you can achieve various responses. Because of this, it is possible to increase your strength without adding bulk, and it is also possible to increase both. When you stop stimulating the muscle, your muscle composition may return to normal or, depending on your regular routine, it may simply stay as is. Unlike fat, each muscle can be specifically targeted, so you can choose the specific area you would like to improve. With that said, realize that while you can work your abdominal muscles, for example, you may not see the enhanced shape and form if you have a thick layer of fat covering them up.