Chronic and Postprandial Metabolic Responses to a Ketogenic Diet Compared to High-Carbohydrate and Habitual Diets in Trained Competitive Cyclists and Triathletes: A Randomized Crossover Trial

Austin J Graybeal; Andreas Kreutzer; Kamiah Moss; Petra Rack; Garrett Augsburger; Robyn Braun-Trocchio; Jada L Willis; Meena Shah

doi:10.3390/ijerph20021110

Chronic and Postprandial Metabolic Responses to a Ketogenic Diet Compared to High-Carbohydrate and Habitual Diets in Trained Competitive Cyclists and Triathletes: A Randomized Crossover Trial

Int J Environ Res Public Health. 2023 Jan 8;20(2):1110. doi: 10.3390/ijerph20021110.

Authors

Austin J Graybeal¹, Andreas Kreutzer^{2

3}, Kamiah Moss^{2

4}, Petra Rack², Garrett Augsburger², Robyn Braun-Trocchio², Jada L Willis⁵, Meena Shah²

Affiliations

¹ School of Kinesiology & Nutrition, College of Education and Human Sciences, University of Southern Mississippi, Hattiesburg, MS 39406, USA.
² Department of Kinesiology, Harris College of Nursing and Health Sciences, Texas Christian University, Fort Worth, TX 76129, USA.
³ School of Health Promotion and Kinesiology, College of Health Sciences, Texas Woman's University, Denton, TX 76209, USA.
⁴ Physical Medicine and Rehabilitation, Baylor Institute for Rehabilitation, Dallas, TX 75246, USA.
⁵ Department of Nutritional Sciences, College of Science & Engineering, Texas Christian University, Fort Worth, TX 76129, USA.

Abstract

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.

Keywords: carbohydrate oxidation; endurance athletes; endurance performance; energy expenditure; fat oxidation; high-carbohydrate diet; ketogenic diet; low energy availability; metabolism.

Publication types

Randomized Controlled Trial
Research Support, Non-U.S. Gov't

MeSH terms

Blood Glucose / metabolism
Cross-Over Studies
Diet, High-Fat
Diet, Ketogenic*
Energy Metabolism
Postprandial Period

Substances

Blood Glucose

Grants and funding

This work was supported in part by the Harris College of Nursing & Health Sciences Graduate Student Research Grant.