We give them the same pile of food to eat, every day, for one month. Totaling 4,000 calories, this it’s a diet rich in poultry, beef, rice, and pasta. They have to just sit on the couch and do nothing for that month.
What do they look like at the end of the month? Remember they have had identical activity levels (none) and eaten the exact same amount of food. At the end of that month, Mr. Skinny would have gained a great deal of weight. Mr. Muscle would remain the same.
How can this be? Why would Mr. Muscle automatically burn up more calories than Mr. Skinny, who got fat as a result of what were excess calories to him? The answer lies in lean body mass. Mr. Muscle carries about 110 more pound of muscle on his frame than Mr. Skinny does. And all that muscle requires more maintenance calories, even if it is just to sit on the couch all day.
The secret to being lean then, of course, is to hold more muscle on your frame. The more muscle you hold, the more calories your metabolism will automatically burn up each day. The less muscle you hold, the fewer calories you need each day.
Mr. Skinny is an example of those habitual dieters you see who can never seem to keep any fat off. Mr. Muscle is an example of the guy you know who never does cardio, yet holds some good muscle and always seems to be at a low body fat anyway. What is his secret? Simple. He holds more muscle.
Bottom line: If you want to lose fat, you need to gain muscle!
Source: http://www.bodybuildingtoday.com/index.php/miscellaneous/bodybuilding-training-gaining-weight-to-lose-weight.html