The Medical and Scientific Commission of the International Olympic Committee assembled a panel of experts in at their offices in Lausanne, Switzerland, to discuss the place of dietary supplements in the nutrition strategy of the high-performance athlete (read the consensus paper). Participants from fields of practice, policy and research were selected because of their experience and expertise in one or more relevant areas, including nutrition, dietetics, physiology, pharmacy, medicine and anti-doping. Detailed discussion papers were prepared in advance of the meeting and were circulated to all participants. The evidence that informed these papers was presented and analysed in depth over the three days of the meeting. The papers are also published in the International Journal of Sports Nutrition and Exercise Metabolism.
Practitioners who work with Olympic and highly competitive athletes know that the pressures of elite sport and the substantial rewards that follow success provide a high level of motivation to adopt any safe and legal strategy that might promise even the smallest performance gain. Dietary supplements operate in this space, whether they promise a large performance boost or just create the fear that an athlete cannot afford to miss out on what their rivals are using. Dietary supplements encompass a wide range of products, including essential nutrients (vitamins, minerals, proteins, amino acids, etc), herbals and botanicals, and specific products with potential for maintenance of health and optimisation of performance. The use of dietary supplements is widespread among elite athletes, as it is in the general population. Users cite many different reasons for consuming dietary supplements, though these reasons are often based on unfounded beliefs rather than on any clear understanding of the issues at stake, and may reflect encouragement from individuals who are influential rather than being experts on this topic.
There is now a widespread acceptance that some supplements can offer benefits to the elite athlete if used appropriately but that some may be harmful to health and/or performance. Benefits from the use of supplements and sports foods may include convenience and provision of a known amount of a key nutrient, as, for example, in the use of protein supplements after training with the aim of promoting training-induced adaptations in muscle and other tissues. Supplements should be used by athletes only when safety is assured - though an absolute guarantee is seldom possible - and a health or performance benefit is likely, but there is limited evidence of efficacy of most supplements. More well-conducted and sports-specific studies research on supplements are needed, as many of the published studies have used inappropriate experimental models and subject populations that are not representative of the elite athlete. Assessment of the evidence requires a consideration of potential limitations to study design, including confounding variables and bias, and of the relevance to real-life practices of elite athletes, as well as the need for verification of the composition of supplements used. Performance changes should be interpreted in light of what is meaningful to the outcome of sporting competition. It must be remembered, though, that absence of evidence of efficacy is not the same as evidence of absence of efficacy.
A comprehensive nutrition assessment is the first step in advising athletes on dietary strategies or medical uses of supplements. Nutrition assessment requires the systematic collection, verification and interpretation of the data needed to identify nutrition-related problems, their causes and their significance. A complete assessment should include dietary evaluation, body composition analysis, biochemical testing, nutrition-focused clinical examination, and patient health and performance history. Assessment should take account of maturation status, sex, ethnicity and culture. The limitations and uncertainties in all of the methods employed must be recognised, though valid and reliable methods are available for some specific nutrients.
A few specific supplements may offer performance benefits to some athletes, but their use requires careful evaluation. Supplements supported by good evidence of efficacy, in at least some exercise models, include carbohydrate, protein, caffeine, creatine, specific buffering agents and nitrate. Because responses seem to vary between individuals and depend on the exercise model used, supplements should be thoroughly trialled in training or simulated competition before implementation into a competition environment. Indeed, it is possible that deleterious responses may outweigh any expected performance-enhancing affect.
Over the past two decades, a new hazard related to supplement use has emerged: inadvertent ingestion of substances that are prohibited under the anti-doping codes that govern elite sport, but are present in some supplement products. In some cases, the level of banned or toxic substances in supplements presents a health hazard for all consumers. In other cases, the content may be too small to cause any health or performance effect but large enough to record an Anti-Doping Rule Violation for athletes who submit to doping tests. These problems may arise from poor quality assurance during production or from deliberate adulteration of otherwise ineffective products.
The lack of evidence to support claims made about a supplement may be ignored by athletes because the stakes are so high: the cost:benefit ratio therefore favours experimentation in the absence of clear proof. The use of dietary supplements should not compensate for poor food choices and an inadequate diet, except as a short-term strategy when nutrient intake is challenged or dietary changes are not possible. Use of products that have been subjected to one of the available quality assurance schemes can help to reduce, but not eliminate, the risk of an inadvertent doping infringement. Vulnerable populations, including especially young athletes, may require particular support in making choices about supplement use. In general, use of supplements by young athletes is discouraged except when full evaluation of nutritional status suggests that it is warranted.
The full text of the review paper can be found at: http://dx.doi.org/10.1136/bjsports-2018-099027
