Without a doubt, protein is the most important supplement available for muscle mass, energy, recovery and general health. Most protein powders contain a high amount of amino acids needed for muscle repair and growth. There are many types of protein on the market. Whey is the most popular kind of protein powder and is one of the fastest acting proteins available. Casein is the second most popular and is slow acting in comparison to whey protein. Whey protein is ideal in between meals and before and after training. Casein protein is ideal if you are going more than 3 hours without food and also last thing at night.