The study, published in the British Journal of Nutrition, 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 Lewis James from Nottingham Trent University.
Fluid retention
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.
Improved retention
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.
The authors reported ingestion of the 65 grams per litre carbohydrate solution resulted in a significant fluid deficit, despite taking in a fluid volume equivalent to 150 percent of body mass lost.
Substituting 25 grams per litre of the carbohydrate (maltodextrin) for 25 grams of milk protein increased fluid retention, and resulted in a less negative net fluid balance. The researchers noted that although net fluid balance for the milk protein solution was still negative, it was not found to be statistically different from pre-exercise levels.
Effective composition
James and his co-workers stated that their research suggests that “gram for-gram, milk protein is more effective at augmenting fluid retention than carbohydrate.”
“These findings emphasise the importance of drink composition in ensuring complete recovery of fluid balance after exercise-induced dehydration,” wrote the researchers.
“Although not determined during this investigation, it is likely that the success of the carbohydrate–milk protein solution at maintaining fluid balance is due to a reduced rate of gastric emptying and, therefore, overall fluid uptake, although further investigation should be conducted in order to determine this relationship,” they added.
Source: British Journal of Nutrition
Published online ahead of print, doi: 10.1017/S0007114510003545
“Effect of milk protein addition to a carbohydrate–electrolyte rehydration solution ingested after exercise in the heat”
Authors: L.J. James, D. Clayton, G.H. Evans