Post workout rehydration: which drink fares the best?

Dr Andy Blannin with Professor Alice Roberts

Which drink should we reach for after a hard work-out? Exercising in a hot environment leads to dehydration, so we need to consume fluids in the post-exercise period in order to replenish the fluid lost through sweating. For optimal rehydration, is it necessary to consume a sports drink, or are other drinks as good? Dr Andy Blannin (Senior Lecturer in Exercise Metabolism) looks at this issue with Professor Alice Roberts (Professor of Public Engagement in Science at the University of Birmingham) on Britain’s Favourite Foods: Are They Good For You? (21:00, Tuesday 14 April, BBC2).

Andy, Alice and 12 undergraduates reconstructed an experiment in the School of Sport, Exercise and Rehabilitation Sciences this January. On three separate occasions the volunteers were dehydrated by exercising in the school’s environmental chamber (35°C and 50% humidity), until they lost 1% of their body weight.

The dehydrated volunteers then consumed either water, a sports drink or milk. The efficacy of these drinks to rehydrate was assessed by fluid retention - measured via urine output over the next four hours. The volunteers returned on two further occasions to repeat the procedures with the other drinks.

Dr Blannin explained, “The results showed that milk was the best drink to consume for post-exercise rehydration, and most of the fluid ingested on the milk trial was retained.  In contrast, after consuming the sports drink or water, more of this fluid was lost as urine, leaving the volunteers slightly dehydrated.”

One of the reasons for this difference is likely to be the composition of the milk, which is released more slowly from the stomach due to the protein and fat within the milk. The slower delivery of the milk from the stomach to the intestine means the fluid does not get absorbed into the bloodstream so quickly. The other drinks, in contrast, are rapidly absorbed flooding the bloodstream, which triggers a diuretic response, leading to urine production and fluid loss. 

Dr Blannin added, “The idea of drinking milk after a grueling work-out might seem odd to people, and some of our volunteers found it a little difficult to stomach, but it really is an excellent post-exercise recovery drink.”

Britain’s Favourite Foods: Are They Good For You? is available on the BBC iPlayer till 14 May 2015.