|Runners who drink too much during race finish last|
Marathon runners have been persuaded to drink too much during a race by the drinks industry, researchers have said, as a study finds those who shed more of their body weight finish faster.
Athletes have been repeatedly told that even marginal dehydration can harm their performance leading to a booming market for sports drinks.
However a new study has found that marathon runners who finished a race fastest had also lost the largest proportion of their body weight. This suggests they did not drink more than their body needed, it was concluded.
Conversely those who actually gained weight during the race, performed the worst, the research found
The results are published in the British Journal of Sports Medicine.
The research involved tracking 643 competitors who finished the 2009 Mont Saint Michel Marathon in France – a distance of 42 kilometres (just over 26 miles).
They were all advised to drink 250ml of either water or a sports drink every 20 minutes during the race.
It was found that the fastest finishers, those who completed the course in under three hours, lost three per cent or more of their body weight.
Those finishing in between three and four hours lost an average of 2.5 per cent of their body weight and those finishing in more than four hours lost two per cent in weight.
Almost one in ten runners actually gained weight and finished the slowest.
Co-author Professor Timothy David Noakes, Department of Human Biology, University of Cape Town, wrote in the journal: "Interestingly, 9.5 per cent of runners in this sample overdrank and gained body weight during the race.
"There is no benefit to overdrinking during exercise. Instead significant overdrinking will cause potentially fatal exercise-associated hyponatraemic encephalopathy.
"Since overdrinking cannot be produced by internal biological signals, the high prevalence of overdrinking must be due to behavioural conditioning.
"Such overdrinking was neither promoted by the information provided by the race organisers nor encouraged by the relatively few aid stations located only every 5km.
"Rather, such overdrinking most likely results from specific messaging directed, especially by the sports drink industry."
He said that runners would not ignore their thirst when drinks were readily available so it must be that even those who lost body weight drank sufficient amounts to prevent them falling ill.
A spokesman for the British Soft Drinks Association said: “Sports drinks are designed with the help of the latest sports science and there is a range of them, each intended for a specific sporting purpose or need.
"As you would with the equipment or footwear you need, it makes sense to choose the right drink for your sporting activity.”