Mass gainers are a blend of protein and carbohydrates which are higher in calories than standard protein shakes. See More The increased calories and the addition of carbohydrates in mass gainer formulas can help users make greater muscle and size gains as well as enhancing gainers are the next step up from standard protein powders for those who wish to make greater gains in size and strength. Mass gainers are essentially a protein shake that has had the calories increased with the addition of carbohydrates. As building muscle is a calorie intensive process, more calories than the body requires to maintain weight are needed to fuel the process of hypertrophy and as carbohydrates, or more precisely, the muscle glycogen they turn into when ingested, are the body’s primary energy source, an abundance in the diet provides the foundation required for growth.
It's also a good idea to add in a protein source that digests at a medium rate -- one that's slower than whey but faster than casein. This bridges the gap, so to speak, between whey and casein to provide a fast yet steady and long-lasting supply of amino acids to your muscles. Two of the best proteins to consider here are egg protein and soy protein. Not only do these proteins digest at a different rate than the milk proteins whey and casein, but they provide other benefits that the milk proteins don't. And no, soy does not decrease a man's testosterone levels or increase estrogen, as research confirms.