I remember sitting in a hipster cafe. It was 12 years ago. CrossFit still felt like Fight Club. A man high up in the underground world said to me casually, “I just eat bacon and crush whatever.”

I knew this probably wasn’t the best chronic choice for anaerobic performance or muscle gain, but the comment was so absurd to me at the time I couldn’t even formulate an educated opinion on the topic. 

Now I can.  

Keto + CrossFit =  Shredded Beef

Doesn’t matter if you are male or female, if you smash CrossFit and Butter you will look like Matt Fraser in two…maybe three weeks. 

And look you can snatch all the 25s. Veteran move Shutterstock.


We actually now have two studies that looked at the potent Kool-Aid Combo of Keto and CrossFit.

The first is a study by Kephart et al. 2018 [1] which took 12 kind of trained subjects (FFMI of 21 and a 1RM Back Squat of 245lbs) and put them through 12 weeks of CrossFit. They trained about two times per week and one group ate Keto and one group kept eating what they had been eating.

At the end of the 12 weeks, the Keto CrossFit group lost 5.5 lbs of fat and the Control CrossFit group well…didn’t.

But, neither group put on any muscle and both groups didn’t really get that much better at CrossFit, although they all could do about 8 more pushups after 12 weeks.

The second study by Gregory et al. 2017 [2] was a 6 week study in 27 not very trained individuals.

Both groups hit four CrossFit workouts per week and again one group ate Keto and one group didn’t do anything to their diet.

Similarly, the Keto group lost about 6 lbs of fat…in half the time.

But, again neither group put on any muscle.


Ok, so it looks like nobody made gains or even really got that much better at CrossFit. 


Thus, is the problem Keto or CrossFit?


Well, we just so happen to have a nice little study by Vargas et al. 2018 [3] which had 24 kind-of-trained individuals hit a solid 4 day-a-week Upper/Lower split for 8 weeks. One group was Keto and the other group ate 55% Carbs, 20% Protein, and 25% Fat and thankfully both groups were instructed to eat 2 g/kg of protein.  They also had a small control group that didn’t do anything.

The Keto group lost about 2.5 lbs of fat, but gained no muscle.

The Normal diet group lost no fat, but gained 3 lbs of muscle which isn’t quite as good as the 12 week dreamer bulk study where participants gained 4.4 lbs of muscle (and 4 lbs of fat) [4], but it is pretty much par for the course in this particular population with a solid training protocol and enough protein [5, 6]. These results are consistent with another 10 week Keto and Resistance training study in 18 overweight females [7].

Thus, the problem looks like it might be Keto, but could it also be CrossFit?

On the CrossFit side we have seven studies [8-14] all of which had relatively untrained participants WOD out 2-3 times per week and none of these studies had a dedicated nutritional arm.

Four studies found no GAINZ [9, 12-14]

In the three studies that found a significant effect on muscle mass, one found a muscle gain of about 2.2 lbs in 8 weeks in physically inactive subjects [11], another with a questionable body composition analysis found a 1 pound increase in females and a 3 lb increase in males [10] in 12 weeks, and the most questionable of all in 8 cancer survivors found that CrossFit put on 8.4 lbs of muscle in just 5 weeks, all while simultaneously losing 7.3 lbs of fat (suspicious).

Thus, the majority of studies found no effect on muscle gain even in untrained subjects and two of the studies that found an increase in muscle either utilized a questionable body composition analysis or were in cancer survivors. 

Do I think that CrossFit can put on muscle in untrained subjects? YES, probably but I need to see the individual data because they might just be spending the majority of their time learning the vocabulary and how to double-under.


To summarize…

“Just Eat Keto” + CrossFit = Potentially Lose 2.5-3 Kilos of Fat. No Muscle Gain. 

Structured Keto “Gain” Protocol + Upper/Lower Split = Lose 1 Kilo of Fat and No Muscle Gain. 

CrossFit Alone – Meh Maybe Maybe 1 Kilo of Muscle Gain in Novices. 


But, what about the “Just Eat Keto” for weight loss…how does that compare to the first two trials?

Harvey et al. 2019 [15] is the closest thing I could find inside of this time domain and they had a structured Keto program for 3 weeks and then had subjects eat kind-of ad libitum for 9 weeks.

Subjects lost about 4 kilos of body weight over the 12 weeks (maybe 25% of that was muscle without an exercise arm so likely 3ish kilos of fat) which is comparable to the first two studies we reviewed where muscle mass was preserved. But, with sufficient protein intake even vacuum cleaning 110 minutes a week [16] can preserve muscle mass in untrained weight loss subjects so not a huge win there, but a win nonetheless. 

In comparison, if you take a much more structured dietary weight loss program like Veum et al. 2017 [17] who had subjects weigh and measure and submit their food intake 5 days per month you see about 10 kilos (22 lbs) of weight loss in 12 weeks regardless of the carbohydrate content.

So wait you are saying that “Just Eat Keto” and “Do CrossFit” is not the best approach for Body Composition changes whether you want to lose fat or gain muscle?

Probably not.

And if you are advanced and trying to get even more jacked VERY VERY probably NOT.

This is not to say that there are not people who have achieved phenomenal results utilizing Keto and/or CrossFit, but they likely have a more planned approach and thus are not really just eating Keto while doing Constantly Varied High Intensity Exercise.

Finally, even if we play the Whack-A-Mole mechanism game, neither Keto nor CrossFit have much of an UP side for hypertrophy.


Potential Negative Mechanisms of Keto and Hypertrophy

Reduced mTOR [18-21]?

Reduced Glycogen Content [22, 23]? Reduced PDH activity[24-26] and reduced recoverability and repeat volume tolerance? 

Reduced appetite [27]?


Potential Positive Mechanisms of Keto and Hypertrophy

Reduced inflammation [28]…I would bet the farm this isn’t going to matter in trained subjects with solid body comp numbers though.

Increased Protein Intake…you don’t have to be low carb or Keto to eat sufficient protein.

Increased strength to power ratio…Yes, this has been found previously [29, 30] and Keto looks like it can be a viable cutting strategy for weight restricted power sports, but that is a very different research question than the one we are analyzing here.


Potential Negative Mechanisms of Random CrossFit Workouts and Hypertrophy

Muscle Confusion AKA you don’t really get good at any one exercise enough to overload it and if you are programming and having a periodized approach you by definition are not doing CONSTANTLY varied high intensity training anymore. This lowering of effective volume may have been why males who had a starting FFMI of around 22 in the Feito et al. [12] study showed a trend towards losing a 2ish lbs of muscle in 16 weeks. Also, CrossFit is the BEST at moving the goal posts and thriving on the learned effect of testing. Oh, you didn’t get better at your 5RM Back Squat…but look you can do 20 wall balls 3 seconds faster and you added 5 reps to your Cindy total just by getting better at Cindy.

Interference Effect [31-33] – Trying to do everything all at once probably isn’t going to work for very long. A good CrossFit coach can likely dissipate the interference effect, but again by definition not CrossFit anymore.

Injury Risk – we don’t want to get sued, but 3.1-3.2 injuries per 1000 hours[34, 35] is 15x more than 0.24 per 1000 hours for bodybuilding [36]. The injury risk of high rep snatching in fatigue may in fact be overstated as a recent epidemiological study by Feito et al. found an injury risk of 0.27 injuries per 1000 hours [37]. However, this is the same lead author who published two of the studies above on CrossFit and body comp and whose research gate profile reads, “The long-term goal of our laboratory is to evaluate psychobiological mediators that enhance participation in high-intensity functional training, and examine the effectiveness of HIFT.” Biased?

High systemic fatigue with compound lifts combined with high relative perceived exertion without peripheral or muscular progressive overload. 2 Stones – Zero Thunder-Jacked Hypertrophy Birds.


Potential Positive Mechanisms of Random CrossFit Workouts and Hypertrophy

Effort and Adherence – People love love CrossFit and they have done the community fitness tribe business better than anyone. The model has the potential to squeeze every ounce of effort out of you. It will show you what you are capable of, but if you don’t succeed people generally don’t blame the programming or CrossFit…they blame their effort.  

Unfortunately, working hard doesn’t guarantee results and my biggest beef with Keto and CrossFit for hypertrophy is that they are both needlessly difficult for ZERO potential hypertrophy upside.

I got my start in the CrossFit world. I drank all the Kool-Aid. But, I never just showed up and did random CrossFit workouts. We always trained to get better at CrossFit and I was always on some kind of team and we kind-of maybe had a sports science approach. Yea, there was plenty of complete fitness debauchery involved, but it was the first time after college baseball that I really tried and started chasing numbers again.

Yet, I would have been classified as highly trained even when I started CrossFit and anecdotally I can’t remember too many untrained people getting that much better at CrossFit just completing haphazard workouts. Since I “completely” left CrossFit six years ago I have had plenty of clients come to me who have been running CrossFit for 5+ years. They think they are trained because they know what a snatch and a power clean are, but unfortunately they generally have a training age of about 6 months to a year and this comes with a laundry list of injuries and a mild addiction to getting their ass kicked. But, there is one thing that I am forever grateful for when these type of clients seek out my services…I know they know how to WORK and with some redirection of their effort they can see phenomenal results.

CrossFit does a lot of things well. They focus on being an inclusive community where each workout can be modified to fit your needs. They make fitness fun and constantly make incremental progress real by gamifying everything. But, one’s relationship with CrossFit is only valuable if the rewards outweigh the risks and if the primary reward you seek is body composition changes Random CrossFit and Just Eat Keto are likely NOT your best options.


Future Directions:

At this point, I would like to see case study or case series data of trained subjects moving from an FFMI of 22 to say 24+ in males and maybe 17 to 19+ in females all while eating exclusively Keto. I would hypothesize that this is 100% possible and that these case studies would be publishable given the current state of the Keto and Muscle Gain literature.

We can wish for three year RCT in a highly trained population with the same training protocol and a single independent variable of Keto vs. Not- Keto, but that probably just isn’t going to happen and if we had access to this population with this level of control for this long there are likely other variables we would all like to test instead.

It would also be valuable for the next Keto Muscle Gain study to put the Keto group into a ketogenic state before the initial body composition testing so the noise of glycogen and water loss could be accounted for although Volek’s group recently reported that resting glycogen stores may not be significantly different between ketogenic and non-ketogenic endurance athletes [23] and no difference in fat free mass loss was seen at 4 weeks between the keto and non-keto groups in the Veum et al. study [17]. A cross-over with-in subject design mechanistic study on volume tolerance (with serial glycogen measurements) in trained subjects at different rest intervals on a Keto diet would also be extremely interesting to see.



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