School of Kinesiology & Nutrition, College of Education and Human Sciences, University of Southern Mississippi, Hattiesburg, MS 39406, USA.
Department of Kinesiology, Harris College of Nursing and Health Sciences, Texas Christian University, Fort Worth, TX 76129, USA.
Int J Environ Res Public Health. 2023 Jan 8;20(2):1110. doi: 10.3390/ijerph20021110.
Extreme carbohydrate deficits during a ketogenic diet (KD) may result in metabolic adaptations reflective of low energy availability; however, the manifestation of these adaptations outside of exercise have yet to be elucidated in cyclists and triathletes. The purpose of this study is to investigate the chronic and postprandial metabolic responses to a KD compared to a high-carbohydrate diet (HCD) and habitual diet (HD) in trained competitive cyclists and triathletes. For this randomized crossover trial, six trained competitive cyclist and triathletes (F: 4, M: 2) followed an ad libitum KD and HCD for 14 d each after their HD. Fasting energy expenditure (EE), respiratory exchange ratio (RER), and fat and carbohydrate oxidation (FatOx and CarbOx, respectively) were collected during their HD and after 14 d on each randomly assigned KD and HCD. Postprandial measurements were collected on day 14 of each diet following the ingestion of a corresponding test meal. There were no significant differences in fasting EE, RER, FatOx, or CarbOx among diet conditions (all p > 0.050). Although postprandial RER and CarbOx were consistently lower following the KD meal, there were no differences in peak postprandial RER (p = 0.452), RER incremental area under the curve (iAUC; p = 0.416) postprandial FatOx (p = 0.122), peak FatOx (p = 0.381), or FatOx iAUC (p = 0.164) between the KD and HD meals. An ad libitum KD does not significantly alter chronic EE or substrate utilization compared to a HCD or HD; postprandial FatOx appears similar between a KD and HD; this is potentially due to the high metabolic flexibility of cyclists and triathletes and the metabolic adaptations made to habitual high-fat Western diets in practice. Cyclists and triathletes should consider these metabolic similarities prior to a KD given the potential health and performance impairments from severe carbohydrate restriction.
生酮饮食（KD）期间的极端碳水化合物缺乏可能导致反映能量供应不足的代谢适应；然而，这些适应在运动员中除了运动之外的表现尚未得到阐明。本研究的目的是调查与高碳水化合物饮食（HCD）和习惯饮食（HD）相比，KD 对训练有素的自行车运动员和铁人三项运动员的慢性和餐后代谢反应。在这项随机交叉试验中，六名训练有素的自行车运动员和铁人三项运动员（F：4，M：2）在 HD 后分别遵循 14 天的随意 KD 和 HCD。在 HD 和随机分配的 KD 和 HCD 后 14 天，分别收集禁食能量消耗（EE）、呼吸交换率（RER）以及脂肪和碳水化合物氧化（分别为 FatOx 和 CarbOx）。在每种饮食的第 14 天，在摄入相应的测试餐后，收集餐后测量值。在所有饮食条件下，禁食 EE、RER、FatOx 或 CarbOx 均无显着差异（均 p > 0.050）。尽管 KD 餐后 RER 和 CarbOx 持续较低，但餐后峰值 RER 无差异（p = 0.452），餐后 RER 增量曲线下面积（iAUC；p = 0.416），餐后 FatOx 无差异（p = 0.122），峰值 FatOx（p = 0.381）或 FatOx iAUC（p = 0.164）在 KD 和 HD 餐之间。与 HCD 或 HD 相比，随意 KD 不会显着改变慢性 EE 或底物利用；KD 和 HD 之间的餐后 FatOx 似乎相似；这可能是由于自行车运动员和铁人三项运动员的代谢灵活性以及在实践中对习惯性高脂肪西方饮食的代谢适应。由于严重的碳水化合物限制可能会对健康和表现造成损害，因此运动员在进行 KD 之前应考虑这些代谢相似性。
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