Skimmed milk better than isotonics for post-sport rehydration?

Writing in the British Journal of Nutrition , researchers from Loughborough University's School of Sports and Exercise Sciences report that volunteers in their trial remained hydrated after drinking milk, but remained dehydrated after drinking the other drinks.

"The results of the study are really exciting as they show skimmed milk to produce a significant improvement in re-hydration compared to the other drinks evaluated in the study.

As dehydration can have an impact on performance, it is essential to re-hydrate in preparation for subsequent exercise in order to help maximise one's abilities," said lead author Susan Shirreffs from Loughborough University.

According to market analyst Mintel, the sports drink market in the UK was worth £137m ($252m, €200m) in 2003, and is dominated by isotonic drinks like Lucozade Sport, Powerade and Gatorade.

In the US, the sports drinks market is reported to have generated almost $3bn (£1.6bn, €2.4bn) with Gatorade dominating the market with 82 per cent of the market.

Powerade is a distant second with a reported 13 per cent of the market.

The researchers recruited 11 healthy volunteers (average age 24) for the randomized crossover trial.

Lactose intolerant people were excluded from participating.

The participants performed exercise to lose 1.8 per cent of their body weight and then consumed one of the beverages - the volume drunk was equivalent to 150 per cent of the sweat lost.

Drinks included skimmed milk (0.2 per cent), skimmed milk with added sodium chloride, water, or Powerade.

Urine samples were taken five hours after exercise.

The researchers report that urine excretion over the recovery period was unchanged as a result of drinking the milk, while excretion increased between one and two hours after drinking the water and sports drink.

"It is possible to speculate, based on previously published work, that the ingestion of water and the sports drink resulted in a marked haemodilution, stimulating the formation of urine and the rapid return to a net negative fluid balance," they wrote.

No additional benefit on fluid levels was observed when the milk contained additional salt, said the researchers.

"It is likely that the presence of sodium along with a relatively large quantity of potassium (approximately 45 mmol/l) in milk accounts for the effectiveness of milk at restoring fluid balance following exercise-induced dehydration," they said.

"The results suggest that milk is more effective at replacing sweat losses and maintaining euhydration than plain water or a commercially available sports drink following exercise-induced dehydration by approximately two per cent of initial body mass," added the researchers.

"Given that hypohydration results in an increase in cardiovascular and thermoregulatory strain, and a reduction in exercise capacity in the heat, it is important to ensure that fluid losses accrued during exercise are replaced prior to the performance of a subsequent exercise bout," they concluded.

Commenting on the research, Judith Bryans, director of The Dairy Council, said: "This study joins the growing volume of literature which suggests that skimmed milk is a natural and effective post exercise recovery aid.

Drinking milk is not only a valuable way to re-hydrate the body but also provides an excellent source of energy, protein and a vast array of different vitamins and minerals essential to the good health of hardworking sportspeople and the population as a whole."

In the UK, semi-skimmed, or half-fat milk, now accounts for 60 per cent of total milk sales.

Skimmed milk is also growing in popularity, now accounting for a further 14 per cent of the total.

Source: British Journal of Nutrition Volume 98, Pages 173-180 "Milk as an effective post-exercise rehydration drink" Authors: S.M. Shirreffs, P. Watson, R.J. Maughan