For bodybuilding you need to be able to get as much nutrition from the foods you eat as possible. Bodybuilders have leakygut also. While you have leakygut you will find muscle mass weight gain difficult and recovery times longer. Depends on your overall health.
Still you would need a complete source of protein on top of that to get good gains. People who are vegetarians tend to be leaner. Unless they eat a lot of lentils, beans, seeds and nuts and combine protein sources to make sure they get a complete protein in every meal. Whey is also a good source of protein. A lot of people make a fruit smoothie using the protein powder. That's a lot healthier than just mixing with water or milk. By the way if you by plain yogurt you will see some semiclear liquid -- that's whey. Sally Fallon book (Nourishing Traditions) calls for this a lot in her recipies.