From Ergo Log
Athletes who train hard at high temperatures can drink one shake at the end of a workout to restore their fluid levels and provide amino acids to help their muscle recover. Sports scientists at Nottingham Trent University in England draw this conclusion in the Journal of Athletic Training.
Fluid & casein
Dramatic fluid loss reduces athletes' performance, and restoring fluid balance is a priority after a training session. A sports drink containing sugars works better than just water, but a 2007 study suggests that skimmed milk works better than a fluid containing carbohydrates. [Br J Nutr. 2007 Jul;98(1):173-80.]
Lewis James of Nottingham Trent University suspected that the milk protein casein would form curds in the acid environment of the stomach, and curds are digested relatively slowly, preventing the stomach from being emptied quickly. [Br J Nutr. 2011 Feb;105(3):393-9.] That means that the fluid in milk or in a casein shake only enters the body gradually, and the body is thriftier with it.
Fluid & whey
But what about whey? Whey doesn't form curds and the amino acids in whey enter the bloodstream relatively quickly. Once there they should in theory boost the production of urine – and thus delay fluid balance recovery. James attempted to gain clear up the matter by doing an experiment with 12 male recreational athletes.
James got his subjects to cycle on two different occasions at a temperature of 35 degrees until they had lost 1.7 percent of their bodyweight in the form of fluid. Afterwards the subjects were given one and a half times the amount of fluid they had lost over a period of one hour – on one occasion in the form of a sports drink containing carbohydrates, on the other occasion a sports drink containing carbohydrates and whey.
The sports drink with whey restored the fluid balance just as well as the sports drink containing only carbohydrates, James concluded after analysing the amount and osmolality of the urine.
"Muscle protein synthesis after exercise has been shown to be greater with the coingestion of protein and carbohydrate than with ingestion of an isoenergetic amount of carbohydrate", the researchers write.
"Therefore, our findings suggest that although retention did not differ between a solution of whey protein isolate and carbohydrate and a solution of isoenergetic carbohydrate, the potential benefits for muscle glycogen resynthesis and muscle protein synthesis might make the addition of whey protein isolate to a rehydration solution attractive in some athletic situations."
J Athl Train. 2012 Jan-Feb;47(1):61-6.