Keto for Athletes

Can athletes be successful on a keto diet? Can a triathlon thrive on a diet with only 20 grams of carbs a day? You’ve most likely heard that carbohydrates are necessary for energy, so how can you run a marathon without eating carbs. You’ve read about endurance athletes carb loading before events. You’ve seen the all the gels they take during races. How can an athlete consume the majority of their calories from fat and be successful?

Several recent studies have examined the ketogenic diet and athletes. While these are small studies, they have shown that athletes, even endurance athletes, can be successful on the keto diet or a low carb, high fat diet.

A 2017 study of twenty male endurance athletes who normally ate a carbohydrate-based diet, self-selected either a high-carb diet (n=11, 65%CHO /14%PRO /20%FAT) or low carb, keto diet (n=9, 6%CHO /17%PRO /77%FAT). Both groups went through the same training: endurance, strength, and HIIT. The athletes followed the diet for 12 weeks and then completed body composition assessment, 100 km time trial, six second sprint, and critical power test. During the post-intervention testing, the high carb group consumed 30-60 g carbs/hr the keto group consumed only water and electrolytes.

Conclusion: The endurance athletes on a keto diet reduced their body fat percentage, increased fat oxidation, increased sprint power, and performed better on a critical power test than athletes on a high-carb diet over the course of 12 weeks (1).

In another 2017 study, 27 non-elite CrossFit athletes were randomly assigned to either a low carb diet (n=12, <50 g carbs) or told to maintain their usual diet (n=15). The athletes participated in four CrossFit sessions per week for six weeks. The study tested body fat percentage, fat mass, lean body mass, and performance.

Conclusion: The low carb group had a significant decrease in body fat percentage and fat mass. Lean body mass and performance were the same in both groups (2).

And more recently, a 2018 pilot study examined 16 expert triathlon athletes who followed either a keto diet (n=8) or a Western diet (n=8) for five weeks. The study tested: VO2max, Peak Power Output, Respiratory Ratio, Heart Rate, VO2, blood lactate during a one hour cycle at 45% of PPO, and body composition.

Conclusion: The Keto Diet group showed a significant increase in VO2max, increase in PPO, decrease in fat mass, decrease in lactate, and decreased RR. There was no change in lean body mass or time to exhaustion (3).  

Still skeptical? Check out these professional athletes who follow Ketogenic or LCHF diets:

  • LeBron James

  • Australian Rugby Team

  • Chris Fromme - Three time winner Tour de France

  • Paula Newby-Fraser - Eight time Ironman World Champion

  • Zach Bitter - Ultramarathoner, holds the 100-mile American record and 12-hr world record (4)

Curious about trying a ketogenic or LCHF diet to help improve your athletic performance, check out The Art and Science of Low Carbohydrate Performance by Jeff Volek, PhD, RD and Stephen Phinney, MD, PhD.  


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