The study suggests that a replacing 25 grams per liter of carbohydrate with milk protein in standard carbohydrate-electrolyte sports drink can improve the rehydration ability of the drink by improving fluid retention.

“The results of the present investigation indicate that, when matched for energy density, fat content and electrolyte concentration, a carbohydrate–milk protein solution is better retained than a carbohydrate solution after exercise-induced dehydration,” wrote the researchers, led by Dr Gethin Evans from the Manchester Metropolitan University in the UK.

Rehydration after exercise has been well investigated, with previous research showing that for complete recovery of fluid balance, both the volume and composition of a rehydration fluid are vital.

It is known that the volume of the fluid consumed must be greater than the volume of sweat lost, and account for ongoing – post exercise – fluid losses. However, for the effective, long term, maintenance of fluid balance the composition of the fluid is also of critical importance.

On top of the addition of electrolytes, such as sodium and potassium, to rehydration fluids, the consumption of solutions containing protein has been suggested to offer advantages in terms of fluid retention. With previous research demonstrating that low-fat milk containing proteins is brought about better fluid retention than either a carbohydrate–electrolyte sports drink or water.

The new study investigated these findings in more details, examining the effects of milk proteins on rehydration after exercise in the heat.

The results observed that a solution made up of 40 grams per litre of carbohydrate and 25 grams per litre of milk protein was offered better fluid retention than a 65 gram per litre carbohydrate solution – as a post exercise rehydration drink.