Casein vs whey is a long debated topic, and whilst they are very similar there are very clear differences between the two. Both casein and whey are complete proteins found in milk that are rich in amino acids. However, casein is absorbed by your body at a much slower rate than whey. This slower absorption rate means that casein provides your cells with small amounts of amino acids over a longer time. Many therefore believe that whey may be better for muscle-building and casein better for preventing muscle breakdown.