Background The ketogenic diet has become popular among endurance athletes as a performance enhancer. This paper systematically reviews the evidence regarding the effect of the endurance athlete’s ketogenic diet (EAKD) on maximal oxygen consumption (VO 2 max) and secondary performance outcomes. Methods PubMed and Web of Science searches were conducted through November 2019. Inclusion criteria were documentation of EAKD (< 50 g daily carbohydrate consumed by endurance athletes), ketosis achieved (measured via serum biomarker), VO 2 max and/or secondary outcomes, English language, and peer reviewed-publication status. Articles were excluded if they were not a primary source or hypotheses were not tested with endurance athletes (i.e., individuals that compete at submaximal intensity for extended time periods). Study design, diet composition, adherence assessment, serum biomarkers, training protocols, and VO 2 max/secondary outcomes were extracted and summarized. Results Searches identified seven articles reporting on VO 2 max and/or secondary outcomes; these comprised six intervention trials and one case study. VO 2 max outcomes ( n = 5 trials, n = 1 case study) were mixed. Two of five trials reported significant increases in VO 2 max across all diets; while three trials and one case study reported no significant VO 2 max findings. Secondary outcomes ( n = 5 trials, n = 1 case study) were Time to Exhaustion (TTE; n = 3 articles), Race Time ( n = 3 articles), Rating of Perceived Exertion (RPE; n = 3 articles), and Peak Power ( n = 2 articles). Of these, significant findings for EAKD athletes included decreased TTE ( n = 1 article), higher RPE ( n = 1 article), and increased Peak Power ( n = 1 article). Conclusion Limited and heterogeneous findings prohibit definitive conclusions regarding efficacy of the EAKD for performance benefit. When compared to a high carbohydrate diet, there are mixed findings for the effect of EAKD consumption on VO 2 max and other performance outcomes. More randomized trials are needed to better understand the potentially nuanced effects of EAKD consumption on endurance performance. Researchers may also consider exploring the impact of genetics, recovery, sport type, and sex in moderating the influence of EAKD consumption on performance outcomes.

中文翻译：

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耐力运动员生酮饮食综述：性能增强剂还是安慰剂效应？

背景生酮饮食已成为耐力运动员中的一种性能增强剂。本文系统地回顾了关于耐力运动员生酮饮食 (EAKD) 对最大耗氧量 (VO 2 max) 和次要表现结果影响的证据。方法 PubMed 和 Web of Science 搜索一直进行到 2019 年 11 月。纳入标准包括 EAKD（耐力运动员每天消耗的碳水化合物<50 g）、达到的酮症（通过血清生物标志物测量）、VO 2 max 和/或次要结果，英语语言和同行评审的出版状态。如果文章不是主要来源或假设没有经过耐力运动员（即长时间以次最大强度比赛的个人）测试，则将其排除在外。研究设计、饮食构成、提取并总结了依从性评估、血清生物标志物、训练方案和 VO 2 max/次要结果。结果 搜索确定了七篇报道最大摄氧量 2 和/或次要结果的文章；其中包括六项干预试验和一项案例研究。VO 2 最大结果（n = 5 项试验，n = 1 案例研究）是混合的。五项试验中有两项报告了所有饮食中 VO 2 max 的显着增加；而三项试验和一项案例研究报告没有显着的 VO 2 max 结果。次要结果（n = 5 项试验，n = 1 个案例研究）是疲劳时间（TTE；n = 3 篇文章）、比赛时间（n = 3 篇文章）、感知用力评级（RPE；n = 3 篇文章）和峰值功率（n = 2 篇文章）。其中，EAKD 运动员的重要发现包括 TTE 降低（n = 1 条）、RPE 升高（n = 1 条）、并增加了峰值功率（n = 1 篇文章）。结论 有限且异质性的研究结果无法确定关于 EAKD 对性能益处的功效的结论。与高碳水化合物饮食相比，EAKD 消耗对最大摄氧量 2 和其他表现结果的影响有不同的发现。需要更多的随机试验来更好地了解 EAKD 消耗对耐力表现的潜在细微影响。研究人员还可以考虑探索遗传、恢复、运动类型和性别在调节 EAKD 消费对表现结果的影响方面的影响。关于 EAKD 消耗对 VO 2 max 和其他表现结果的影响，有不同的发现。需要更多的随机试验来更好地了解 EAKD 消耗对耐力表现的潜在细微影响。研究人员还可以考虑探索遗传、恢复、运动类型和性别在调节 EAKD 消费对表现结果的影响方面的影响。关于 EAKD 消耗对 VO 2 max 和其他表现结果的影响，有不同的发现。需要更多的随机试验来更好地了解 EAKD 消耗对耐力表现的潜在细微影响。研究人员还可以考虑探索遗传、恢复、运动类型和性别在调节 EAKD 消费对表现结果的影响方面的影响。