What happens when you take 74 NCAA Division III football players and give them either A.) a protein shake containing whey, B.) a protein shake containing casein, or C.) a protein shake made up of whey plus casein?
Pretty much the same thing it turns out. Since these guys were all training as hard as possible (trying to get a starting job on the team, presumably), and following the lifting and training routine outlined by their coaches (presumably strength and conditioning specialists), I really believe that these results are highly applicable to the real world.
At the end of 8 weeks there were no observed differences in overall performance (1rm lifts, 40 yard dash time, etc…) between the groups, although the casein group ended up losing more fat mass than either the whey or whey + casein groups.
In highly trained athletes (those playing collegiate football, in this case), giving them an extra 40 grams of protein (a whopping 160 calories per day) regardless of the source, just isn’t going to do much in terms of registering performance gains over placebo.