If you don't replace it immediately by consuming carbohydrate, your body will synthesize it from protein stores. That means that the protein that could have gone to making your muscles bigger was used instead to fuel normal body and brain functions. Many strength trainers think that they need massive amounts of protein to gain weight. But studies show that the body can synthesize no more than 1.9 grams of protein per kilogram of body weight. Any excess gets stored as fat.
Protein is important but in moderate amounts.
The creatine advantage. One way to jumpstart your weight gain program is to use a dietary supplement called creatine for a month or more. Creatine is a legal and safe supplement, and using it according to directions, along with a good resistance training program as outlined above, usually leads to a weight gain of five to eight pounds in four weeks. The increased weight is accompanied by increased strength, too. Be a sprinter.