Protein is the building block of muscles. This is why bodybuilders consume protein foods to help their muscles recovery and grow. There are many different protein products on the market with the most common being made from Whey. A whey protein isolate is designed to be very low in carbs and easily digested for post workout to get protein to the muscle as quickly as possible. Mass gainers have carbs added to provide more calories for the hard gainers wishing to bulk up. Casein is a slow digesting protein and is suitable for night time usage as protein uptake is extended over a longer period. There are also Vegan protein powders which are made from plant sources.