Milk contains both whey and casein protein. Whey digests faster while casein is thicker and more slowly digesting. How to put them to best use is a matter of debate, and a study published in the International Journal of Sport Nutrition and Exercise Metabolism weighs in with new research on both proteins, including a mix of the two.

A group of 31 men with weight room experience took part in a 9-week resistance training program. After each training session, subjects consumed 20 grams of whey protein, 20 grams of casein protein or 20 grams of protein consisting of equal parts whey and casein.

Although there was greater availability of the BCAA leucine after consuming whey compared to casein or the protein blend, muscle size and strength gains were similar across all 3 post-workout protein shakes after 9 weeks of training.