Could Sports Drinks be improved with the addition of protein? That question has long gripped physiologists and nutritionists. It’s well established that the carbohydrates (sugars) that sweeten most sports drinks aid performance. They provide immediate fuel for straining muscles, keep blood-sugar levels stable and allow you to work out for a longer period of time or at a higher intensity, or both, than if you don’t swallow any extra fuel. But why wouldn’t taking in protein, together with carbohydrates, during a workout or race make you even more speedy and durable? Protein, after all, is what muscles fundamentally are made of, so it seems reasonable to imagine that adding it to sports drinks could provide some additional benefit.

But to date most studies have not shown that to be true. Some earlier experiments that did find athletic-performance benefits from protein-enhanced sports drinks used protein beverages that contained more calories than the carbohydrate-only versions and, as some critics pointed out, the extra calories rather than the protein, per se, probably provided the benefit. More typically, most studies came to the same conclusion as one published earlier this year in the journal of the American College of Sports Medicine. For that study, cyclists consumed a carbohydrate sports drink or one enriched with whey protein while they warmed up with two hours of steady-state cycling and then completed a strenuous one-hour time trial. The researchers found no benefit from the protein drink. The cyclists downing it didn’t produce more power while pedaling or cover more miles during the time trial, nor did they harbor fewer markers of muscle damage the next day. The protein didn’t hurt their performance, but it didn’t help in any measurable fashion, either.