You can get plenty of protein in your diet, but protein powder has other advantages: It's convenient and generally lower in calories than an entire "high protein" meal. Drinking a protein shake after every workout speeds muscle recovery and supplies your body with the amino acids needed for muscle growth. There are two widely used proteins: whey and casein. Whey is absorbed more quickly by the body, while casein is digested slowly-providing the body with a longer-lasting supply of muscle-building nutrients. That's why many researchers recommend taking a mixture of the two to help sustain the release of amino acids into the blood for as long as possible.