Understanding if dietary supplements are ergogenic and how they should be used, depending on individual goals and requirements, is key to the success of nutritional interventions.
Some research suggests that elite players may respond to supplementation differently when compared to amateurs, and differences in the methodology of each study may lead to misleading results. For example, a recent systematic review and meta-analysis of nitrate supplementation revealed no ergogenic effect in well-trained endurance athletes, but performance benefits were observed in recreationally active, young, healthy men.
Another important aspect has to do with the differences observed among elite and amateur players; elite players have better physical performance indicators than amateur players, meaning that some dietary supplements when used among amateur athletes may improve their athletic performance while with elite players may be useful to maintain performance.
The authors of the current review, from Portugal Football School, Portuguese Football Federation, argue that literature about the use of dietary supplements within elite soccer players is still scarce. They note that the fact that elite soccer players often cope with very competitive and congested calendars may reduce their willingness to participate in research work, and this might be the reason for most studies being conducted with recreational or trained players, or athletes from other sports.
Therefore, they conducted this systematic review to provide a comprehensive overview of the effects of dietary supplements on the athletic performance of highly trained, elite, and world-class adult soccer players.
The review was the first to approach dietary supplements for athletic performance exclusively in highly trained and elite soccer players.
The authors conclude that the results of this systematic review may contribute to increasing confidence in using dietary supplements such as creatine monohydrate, protein, and caffeine.
However, they warn: "Nitrate and tart cherry supplementation, typically available in the form of drinkable concentrates, should be evaluated mindfully, as its efficacy depends on several factors.
"Finally, several substances still lack evidence for performance benefits in highly trained players, meaning extra caution should be taken when considering its use – in the case of yohimbine, its use is strongly discouraged."
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The systematic review involved studies enrolling soccer players in interventions using dietary supplements (searched in MEDLINE/PubMed, Web of Science, Scopus, and EBSCO databases between June 20th and 24th, 2022).
In total, 18 studies, all of them randomized placebo-controlled trials, involving a total sample of 307 adult highly trained and elite soccer players (244 men and 63 women), met the inclusion criteria and were extracted for qualitative analysis.Caffeine was the most frequent dietary supplement investigated, in the form of beverages, capsule or chewing gum. Four studies assessed creatine supplementation, isolated in different forms or in combination with sodium bicarbonate. Two studies investigated protein supplements (whey vs. soy protein and milk protein vs. placebo). The remaining studies investigated beverages with carbohydrates and electrolytes, tart cherry juice, beetroot juice, a supplementation protocol with sodium bicarbonate and minerals, yohimbine, and Resurgex Plus (a proprietary blend of nutrients). Supplementation protocols ranged from one day to five weeks.
The authors note that various factors may prevent studies from being conducted with higher-level soccer players, making data in this area scarce. For instance, elite players’ longer competitive calendars mean less time for participating in intervention studies, or elite players may feel less available to participate. Therefore, the review authors say health and performance support teams should be cautious in interpreting available evidence.
The report states: "Elite soccer players should seek appropriate nutritional support, meaning better, evidence-based practices regarding food and nutritional strategies. Dietary supplements may be valuable and convenient for meeting players’ nutritional requirements, but this review reinforces that their use requires a critical sense of safety and effectiveness.
"Regularly providing supporting teams with training regarding dietary supplementation can increase their knowledge and confidence, leading to better advice for athletes. Finally, more research on top-tier male and female soccer players is needed to better understand the validity of dietary supplements for highly trained athletes."
Discussing a limitation of this review, the authors note that because they conducted their review according to tiers defined by McKay et al., this might have conditioned the number of eligible studies to be included and might be limited to providing information on many other substances currently available (and used) in elite soccer (e.g. vitamins, probiotics, or omega 3 fatty acids).
Source: Journal of the International Society of Sports Nutrition
"Effects of dietary supplements on athletic performance in elite soccer players: a systematic review"
Authors: Rodrigo Abreu, Catarina B. Oliveira, Júlio A. Costa, João Brito & Vitor H. Teixeira