Efficacy of Low-Carb Ketogenic Diet in Endurance Athletes

by Bianca Garilli, ND, IFMCP

Endurance-trained athletes must maintain excellent physical fitness in order to regularly perform activities requiring large quantities of sustained energy. Nutrition plays a major role in their ability to achieve superior athletic goals. However, athletes often do not meet recommended nutritional requirements based on sport, age and sex.¹

A study conducted in 146 endurance athletes from Lithuania found that 80.8% of endurance athletes used lower than recommended amounts of carbohydrates in their diet, while more than 70% of the athletes consumed higher than recommended levels of total fat, saturated fat, and cholesterol.¹ Female athletes demonstrated the largest nutrient gaps, with low intakes of carbohydrates, dietary fiber, protein, omega-3 fatty acids, B vitamins, potassium, calcium, phosphorus, iron, manganese, and zinc.¹ Age also played a role, with adolescent athletes aged 14-18 years frequently consuming either excessive or inadequate protein for their needs.¹

The importance of optimizing and individualizing the diets of highly trained endurance athletes requires constant exploration and analysis of novel approaches to nutrition. A publication in Metabolism studied 20 male endurance-trained athletes who had previously been following a carbohydrate-based diet.² The objective of the study was to determine if altering their diet to a low-carbohydrate, high-fat ketogenic diet (LCKD) would improve body composition and performance outcomes in these well-trained athletes.²

Participants were separated into two groups; the first group remained on a high-carbohydrate (HC) diet (C:P:F* = 65:15:20), and the second group consumed a LCKD (C:P:F = 6:17:77).² Both groups remained on the specified diet for 12-weeks.² During this time, both groups followed an athletic training program including endurance, strength and high intensity interval training (HIIT).² Prior to the start of the study and at the conclusion of the study, both group’s body composition was assessed and participants performed a 100 km time trial (TT), a six second (SS) sprint, and a critical power test (CPT).²

Results:²

• The LCKD group experienced:
  • Significantly greater decrease in body mass and body fat % when compared to the HC group
  • Significantly higher fasting serum beta-hydroxybutyrate (ketone body) when comparing baseline to week 12 measurements
• SS sprint peak power: increased by 0.8 watts per kilogram bodyweight (w/kg) in the LCKD group and decreased by 0.1 w/kg in the HC group
• CPT peak power: increased by 1.4 w/kg in the LCKD group and decreased by 0.7 w/kg in the HC group
• The LCKD group experienced a significantly greater fat oxidation level throughout the 100 km TT

While improvements were noted in the LCKD intervention arm,² further research is warranted to understand the efficacy of the ketogenic diet in different types of athletic performance. A randomized crossover trial demonstrated that the ketogenic diet impaired anaerobic exercise performance in exercise-trained men and women.³

Why is this Clinically Relevant?

• Many endurance athletes are not meeting nutritional recommendations to perform at their peak capacities
• LCKD may improve peak performance in those athletes needing to optimize sprint speed and peak power
• LCKD may support greater fat oxidation during athletic performance
• LCKD lowers body mass and body fat percentage
• Nutritional recommendations should be individualized for sport, age and sex

* C:P:F = indicates the carbohydrate to protein to fat ratio

Link to abstract

Citations

1. Baranauskas M, Stukas R, Tubelis L, et al. Nutritional habits among high-performance endurance athletes. Medicina (Kaunas). 2015;51(6):351-62.
2. McSwiney FT, Wardrop B, Hyde PN, Lafountain RA, Volek JS, Doyle L. Keto-adaptation enhances exercise performance and body composition responses to training in endurance athletes. Metabolism. 2018;81:25-34.
3. Wroble KA, Trott MN, Schweitzer GG, Rahman RS, Kelly PV, Weiss EP. Low-carbohydrate, ketogenic diet impairs anaerobic exercise performance in exercise-trained women and men: a randomized-sequence crossover trial. J Sports Med Phys Fitness. 2018;59(4):600-607.