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Keto and CrossFit: Does It Even Work? Part 1


A short note on studies performed on the ketogenic diet: 

It’s important to consider that many studies that claim to find that keto is “bad” for athletic performance usually don’t allow the study participants to become fully “fat-adapted” to the ketogenic diet.

When transitioning from a carbohydrate-based diet to a ketogenic diet, there is a transition phase in which the body is not using any energy source efficiently. This has been dubbed the “keto flu.”

While the severity of the keto flu varies drastically (I personally had no symptoms at all), there are strategies to minimize this short-term loss of energy. It usually takes the body around 1-2 months to become fully fat-adapted; however, with proper guidance this time can be drastically reduced through smart implementation of the keto diet.

First Study: Effects on Body Composition, Blood Parameters and Performance of the Keto Diet on CrossFit Athletes

Let’s start with an exciting study on keto and CrossFit®. This one is called The Three-Month Effects of a Ketogenic Diet on Body Composition, Blood Parameters, and Performance Metrics in CrossFit® Trainees: A Pilot Study.

This study included two groups, a ketogenic diet (KD) group which followed a 12-week ketogenic diet plan, and a control group. All participants followed a similar CrossFit® training regimen throughout the study.

Findings from the study show that the KD group lost fat mass on average of 12.4%, significantly more than the control group, and no significant change in performance was found (the metrics tested were 1 RM back squat, 400m run times, and VO2Max).

Overall, because the change in total lean body mass was insignificant in both groups and the performance metrics stayed the same, the study shows that the improvement from the KD group was the loss of fat mass and improved body composition.

The study abolishes the notion that keto is bad for Anaerobic Performance.

It’s important to note that, as the body transitions into running off of fat for fuel, the body loses fluids and glycogen at the beginning, and then slowly restores those glycogen stores, so lean body mass measurements can be skewed against keto in the beginning.

What this means for CrossFit® is that better body composition means better movement, and ultimately, better performance. This first study illustrates that the ketogenic diet and CrossFit® can work well together!

Second Study: Keto and CrossFit, Effects on Exercise Metabolism

In this section, we review a study done specifically on CrossFit® athletes who went on the ketogenic diet for about a month. This study determines that Keto and CrossFit® are perfectly compatible.

The study is titled Effect of a four-week ketogenic diet on exercise metabolism in CrossFit®  trained athletes, and looked at recreational CrossFit® athletes. They took pre-measurements, then put them on a four-week ketogenic diet (KD), and performed the incremental cycling test (ICT) again to determine oxygen uptake, carbon dioxide exhalation (which will tell you how much fat and sugar they are burning), and energy expenditure.

What they found was that the males had a notable increase in fat utilisation at intensities up to 80% of VO2max. The females also saw increased fat utilisation. This means that the body can learn to use fat more efficiently during exercise if you begin training your body to use fat for fuel with a ketogenic diet.

I think this bodes well for CrossFit® because, if you are still burning fat at higher exercise intensity, a virtually unlimited fuel source on your body, then you are sparing your precious, limited glycogen stores for those max effort bursts of intensity.

The fat-based athlete is not immediately beginning to deplete their glycogen, but they are saving it for higher intensity efforts.

A higher amount of fat was also burned at higher workout intensities than before the KD.


I hope this has piqued your interest regarding the ketogenic diet and CrossFit®. Hopefully, after reading this, you feel we have established what parameters should be examined for CrossFit® performance and have started to unravel the impact of the ketogenic diet on those parameters.

You now can see that the ketogenic diet and CrossFit can work well together. The KD diet caused better body composition with no loss in performance. But the question still stands, is the ketogenic diet an optimal diet for CrossFit®?

Stay tuned for more posts in this series as we explore the ketogenic diet and CrossFit®. Part Two will examine the ketogenic diet and its impact on various aspects of athletic performance for CrossFit® including strength, gymnastics, endurance, and weightlifting.

Nic and Lindsay are certified Ketogenic Living Health Coaches, accredited by both NASM (National Academy of Sports Medicine) and AFAA (Athletics and Fitness Association of America).

Collectively known as the Millennial Keto Couple, Nic and Lindsay run Millennial Methods to help others fix underlying health issues or optimise their body composition and athletic performance through keto. You can find more of their work under: https://www.millennialmethods.com/8-week-keto-fit-challenge.

All content within this article is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or nutritionist. Please consult a health care professional before drastically changing your diet.

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