'Gym and tonic' – doubts about sports drinks

The Guardian says “Research pours cold water on alleged benefits of sports products”, as specialist sports drinks are a “waste of money”, while the BBC says that “fancy trainers” will not make you run faster.

Both stories are based on research that looked at whether there is any evidence to support the claims made by advertisers for sports-related products, such as sports drinks and trainers. The researchers say they found a significant lack of evidence to support most claims that such products lead to enhanced performance or recovery. Half of all the websites they looked at provided no evidence at all and of those that did half the evidence was judged to be unreliable. Only three of the 74 studies were found to be of high quality and these showed no significant beneficial effect of the product.

This is not to say that it is a good idea to run a marathon in high heels, but it does appear that the hype about expensive trainers making you faster or fitter is not supported by scientific evidence.

The research forms part of a wider investigation into sports products and, in particular, the sports drinks industry, that is being undertaken jointly by the BBC and the BMJ.

There is also compelling evidence that many of the doctors who drew up guidelines about how much, and when, athletes should drink had potential conflicts of interest. For example, three out of the six clinicians responsible for drawing up the 2007 US guidelines on sport and hydration had financial links to sports drinks companies.

One independent expert, Professor Tim Noakes, argues that there is a very simple method of knowing when you need to drink more liquids – thirst.

Where did the story come from?

The study was carried out by researchers from the University of Oxford. There was no specific funding for this study. The study was published in the peer-reviewed medical journal BMJ Open.

It was widely and accurately covered in the media. However, the study does not support the Daily Mail’s claim that sports drinks “can be harmful”.  Although, as Professor Noakes points out, the high calorie count of many sports drinks may not be ideal if you are trying to lose weight through exercise.

What kind of research was this?

This was a systematic assessment of the claims for improved sports performance made by advertisers for a broad range of sports-related products. It also looked at the quality of the evidence on which these claims are based.

The authors say that, currently, the public is faced with a large number of adverts that make claims about enhanced performance and recovery for a wide range of products including drinks, supplements, clothing and footwear. Regulations require that marketing material containing health claims must be supported by documentary evidence and must not mislead consumers. They point out that the marketing of sports products has become “a multi billion dollar industry” and the consumption of “so-called energy drinks” is increasing yearly, but that research in this area is thought to be poor.

What did the research involve?

The researchers searched the top 100 general magazines and the top 10 sport and fitness magazines in the UK and USA and their associated websites, for the month of March 2012 (excluding magazines specifically aimed at body building). They identified all adverts relevant to sports, with claims related to sports performance (such as improvement in strength, speed or endurance) or enhanced recovery (for example, reduced muscle fatigue). They included adverts for sports drinks, oral supplements, footwear and clothing or devices (such as wristbands). Adverts related to weight loss, skin or beauty products and sports equipment were excluded.

They extracted and compiled data from each relevant web page, including any references related to the claims. They emailed all manufacturers with both the claims and the retrieved references asking whether the list of claims and references was complete and whether other data existed to support the claims, including unpublished research.

The authors then obtained full text copies of all cited references and appraised the methods used in the research, assessing first whether the studies were suitable for critical appraisal. They then assessed the level of evidence provided in those that were – using as criteria an established hierarchy – and the risk of bias.  

They also collected information on the participants in the trials included (categorised as “regular people” who do not exercise or compete seriously in sport, amateur athletes and sports professionals), adverse events and other aspects, such as study limitations and whether the intervention had been tested again.

What were the basic results?

The authors viewed 1,035 web pages and identified 431 performance-enhancing claims for 104 different products. They found 146 references underpinning these claims. Of these:

• The authors were unable to perform critical appraisal for approximately half (72 out of 146) of the identified references. This means that the research did not fulfil the established criteria for critical appraisal.
• More than half (52.8%) of the websites that made performance claims did not provide any references.
• None of the references referred to systematic reviews (the highest level of evidence).
• Of the studies that were critically appraised (74), 84% were judged to be at high risk of bias.
• Only three of the 74 studies that were critically appraised were judged to be of high quality and at low risk of bias. Meaning that these were the only studies where the reader could have high confidence in the results. All three of these studies reported no significant effects of the intervention.

The researchers received responses from 16 of the 42 companies they contacted. They received additional reference material from nine companies, five of which were included in their analysis. They also received a bibliography of 174 references on Lucozade, which arrived too late to be included in this study.

In the 74 studies appraised, nearly half of participants were classified as “regular people”, nearly 40% as serious athletes and 10.8% as professionals.

How did the researchers interpret the results?

The researchers say there is a striking lack of evidence to support the claims for enhanced performance or recovery made by the vast majority of sports-related products including drinks, supplements and footwear. They say it is virtually impossible for the public to make informed choices about the benefits and harms of advertised sports products, based on the available evidence.

Conclusion

Perhaps predictably, this study has found little good evidence to support the advertising claims made for a range of sports products including drinks, supplements and trainers. The study was not a systematic review of all the evidence on sports products but rather an examination of the research behind the claims made for them. It is worth pointing out that the study had some limitations that the researchers point out. For example, it is possible the products analysed were at the “worst” end of the spectrum and the manufacturers were not given enough time to respond to requests for information.

The study highlights doubts over sports drinks in particular. The drinks are often marketed as having advantages over water, yet one of the study’s authors is reported in the papers as saying that some of these products contain so many calories that they encourage weight gain and for most people they cancel out the benefits of exercise.

Another important issue is how much people should drink when exercising, especially when performing endurance exercise, for example a marathon. A BMJ feature claims that links between academia and the sports drinks industry has “helped market the science of hydration” in an effort to encourage people to consume sports drinks. The feature says that drinking too much of any liquid can be dangerous and that people involved in sport should “drink to thirst”, which means only drink when they are feeling thirsty.