Its called a body building diet.

I saw a documentary on how Sporting Lisbon build up Luis Figo's physique. They put him on a strict meat and milk diet.

Lets say your some skinnybone ... if you were ask to play in a physically demanding competition, and you don't have body mass .. how are you gonna hold your ground when a big size opponent come running to you.

Of course the only way to build body mass is to eat ... the traditional way is eat protein rich food.