The hydration myth, why less is more

Millions are spent promoting sports drinks, but we do not need them, says Peta Bee

Drink. Before and during your work-out, and some more when you finish. Coconut water, sports drinks, energy fluids, whichever super-fluid takes your fancy, as long as its replete with electrolytes and the unique ability to replace the losses from sweat. For, if we are to believe the hype, a 2 per cent drop in body weight through lost fluid can impair performance by as much as 10 per cent.

But should we swallow such claims? Last week, an investigation by The Times revealed that Coca-Cola, a major sponsor of world sports events, has poured millions into scientific research, and the foundation of the seemingly independent European Hydration Institute — a body that recommends the consumption of the kinds of sports and energy drinks the company sells. More than a dozen British researchers, some from top universities, were found to have financial links with the drinks giant. It sullies, somewhat, the science that has spawned an industry intent on shaping our opinions on our drinking habits.

We’ve all seen the ad campaigns featuring hard-bodied types melting into pools of sweat; watched Premier League footballers and international rugby players swigging sports drinks mid-game; heard how sweat analysis has become de rigueur for top athletes, with physiologists employed to pinpoint the exact amount of liquid needed to keep levels topped up. And we’ve lapped it up. A Mintel report revealed that the sports drinks market grew from £1 billion in 2009 to an estimated £1.5 billion last year, and that more than 61 per cent of Britons had drunk one in 2014.

It’s rare to see a jogger or gym-goer set off now without a drink in hand. Research from Loyola University in Chicago found that 36.5 per cent of recreational runners drink according to a preset schedule or to maintain a certain body weight, while 8.9 per cent drink as much as possible and before they are thirsty.

Tim Noakes, a professor of exercise science and sports medicine and the author of Waterlogged, a book that investigates the “serious problem of overhydration in endurance sports”, believes that the marketing and much of the science is part of a ploy by the soft drinks industry to promote their products to the exercising public as “a medicine that must be ingested to prevent heat illness and optimise sports performance”.

Our appetite for sports drinks does seem at odds with some practices in elite-level sport. The British runner Ron Hill drank nothing when he won the 1970 Commonwealth Games marathon with a time of two hours, nine minutes and 28 seconds. Neither did Mike Gratton when he won the 1983 London marathon, and so it has continued. Kenyan runners adopt what researchers described in the Medicine & Science in Sports & Exercise journal as an “ad libitum fluid intake”, drinking what and when they feel like throughout the day. Likewise, a 2011 study published in the Journal of the International Society of Sports Nutrition found that among the top Ethiopian runners, no fluids were drunk before or during training, with only modest amounts imbibed afterwards. And none of this, it seems, to any ill effect.

There’s an argument that the highly tuned bodies of such sports people behave differently to ours. Even so, the scientific discrepancies are puzzling.

John Brewer, once a director of Lucozade’s sports science institute and now professor of applied sport science at St Mary’s University, Twickenham — a school with no financial links to the drinks industry — says it’s a little-known fact that some fluid loss can help rather than hinder performance, and that “tactical dehydration” is a growing trend among runners, triathletes and cyclists, and not just at an elite level. “Think about it,” Brewer says. “Each litre of fluid lost equates to approximately 1kg of body weight. Carrying around less weight has a positive impact on endurance performance, so people train their bodies to cope with dehydration, rather than fighting to prevent it.”

A report by New Zealand sport scientists, meanwhile, suggests that a 3 per cent drop in body weight through fluid loss doesn’t slow down athletes, while a 2012 paper in the Clinical Journal of Sports Medicine found that elite runners in the heat of the Dubai marathon recorded fluid losses of almost 10 per cent, yet still ran exceptionally fast times.

A few years ago, I took part in a sweat analysis organised by the sports drink company Gatorade, overseen by experts in fluid research from Loughborough University’s school of sport, exercise and health sciences. I was put through my paces, completing a sweat-inducing 40-minute bike ride in a warm and airless room while scientists probed the hi-tech sticking plasters dotted around my body, designed to assess the quality and quantity of my sweat. The result was an eye-opener. I lost just 315ml of it an hour (one to two litres is shed by some people) and a tiny amount of salt (1g), suggesting I am in the camp that can cope with drinking very little.

It was not what I nor, presumably, Gatorade, had expected. What’s more, suggestions that the sugars added to sports drinks increase the body’s absorption of fluid have been disproven. They top up energy “but are only necessary in lengthy endurance events”, Brewer says. “For anything up to the equivalent of a ten-mile run, you are fine with water before hand and when you finish.”

Noakes believes “that the body is adapted for conditions of mild dehydration”, pointing out that our ancestors didn’t have camel bags and water stations to aid their survival when hunting. The blanket approach to drinking before you are thirsty and consuming half a litre or more every hour is not only wrong, he says, but risky. Over-hydration is the cause of the potentially fatal complication, exercise-associated hyponatraemia (EAH), in which blood levels of sodium become excessively dilute. Drinking too much is now a more serious risk than drinking too little in many mass-participation events — a 2011 paper in the British Journal of Sports Medicine reported that 14 runners attended one hospital with EAH after the London marathon.

Dr Mitchell Rosner, a kidney specialist from the University of Virginia school of medicine, recently chaired a group of 16 independent experts from four countries to look into the issue. “We’ve documented at least 14 deaths [from EAH] since 1981,” he says. “The common feature in all cases is excessive water consumption during athletic events. This is driven by misbeliefs that overhydration can improve performance and even prevent dehydration. It is worth noting that data demonstrates mild degrees of dehydration don’t impair performance.”

How, then, should we drink? Guidelines from two decades ago recommended consuming as much liquid as you could tolerate before exercise, that thirst was not a reliable indicator of how much fluid your body needed. In an updated consensus statement published in the Clinical Journal of Sport Medicine, Dr Rosner and his panel stress a reliance on listening to your body. “We recommend using your thirst as a guide,” he says. “If you drink when thirsty, you will not become hyponatremic and you will not suffer from significant dehydration.”

Risks of EAH apply, he said, to sports drinks and water, and Brewer added that anyone exercising moderately for weight loss should avoid sugary sports drinks altogether. “Run 5km and you might burn 340 calories,” he says. “Take a sports drink and you offset 130 of those immediately.” In most cases, water consumed before you leave the house will suffice. “The body is actually incredibly adept at withstanding fluid losses,” Brewer says. “You are not going to crash from dehydration on an average workout.”