As sports drink commercials start promoting their latest concoctions for optimal performance just in time for the Olympics, new evidence from the host country shoots down many of their claims.

The prestigious medical journal BMJ published seven articles on the topic in its current issue, investigating everything from scientists' links to sports drinks companies to the dubious benefits of hydrating with high-caloric liquids.

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"There is a striking lack of evidence to support the vast majority of sports-related products that make claims related to enhanced performance or recovery, including drinks, supplements or footwear," say the researchers.

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For example, Carl Heneghan, MD, of the University of Oxford, says that no more than half of the products reviewed with performance-enhancing claims had no references to studies.

Researchers found 431 claims for various performance enhancements in advertisements for 104 products. But when the researchers tried to find references, they could locate only half of the 146 references provided by the products' websites. And of those, they deemed only three to be legitimate.

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An accompanying commentary sums up the bottom line: Drink or eat a little during prolonged exercise, and encourage your kids to drink water, not sports drinks.

"From our analysis of the current evidence, we conclude that over prolonged periods carbohydrate ingestion can improve exercise performance, but consuming large amounts is not a good strategy particularly at low and moderate exercise intensities and in exercise lasting less than 90 minutes. There was no substantial evidence to suggest that liquid is any better than solid carbohydrate intake and there were no studies in children. Given the high sugar content and the propensity to dental erosions children should be discouraged from using sports drinks," writes Tim Noakes, the Discovery Health Chair of Exercise and Sport Science from the University of Capetown.

Forget pre-hydrating or forcing yourself to down liquid at every water stop in a 10K. The consequences of overhydration can be much worse than the consequences of dehydration.

"People optimise their hydration status by drinking according to the dictates of thirst," Noakes writes. "Over the past 40 years humans have been misled — mainly by the marketing departments of companies selling sports drinks — to believe that they need to drink to stay 'ahead of thirst' to be optimally hydrated."

Not only can just a 2 percent increase in total body water can impair both physical and mental performance, he says, but can result in severe cerebral oedema "that produces confusion, seizures, coma, and ultimately death from respiratory arrest."

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