The Daily Lipid Podcast episode 21 is a recording of Chris Masterjohn's thoughts on doing crossfit while on a ketogenic diet
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The Daily Lipid Podcast episode 21 is a recording of Chris Masterjohn's thoughts on doing crossfit while on a ketogenic diet

In this episode, I give my take on a recent masters thesis paper by Rachel Gregory from James Madison University, which reports a study where just under 30 members of Rocktown CrossFit and Sports Performance were randomized to do CrossFit for six weeks with a normal diet or a low-carbohydrate ketogenic diet.

The ketogenic diet led to weight loss and loss of bodyfat without hurting the performance on a 6-7-minute for-time workout-of-the-day (WOD)-style test involving a 500-meter row, 40 bodyweight squats, 30 ab mat situps, 20 hand-release pushups, and 10 pullups.

Herein, I explain why I think this study does show that the average person can lose weight and get fit with this method, but why it doesn't really get to the heart of the questions I would be interested in, which are these: how would a ketogenic diet impact maximal performance on weight-lifting sets of 5-12 reps, or in sports involving short bursts of energy such as football, basketball, baseball, soccer, and tennis, and do the hormonal adaptations to the diet ultimately have the potential for negative impacts on thyroid hormone, cortisol, LDL-cholesterol, and sex hormones?

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Since the podcast refers to a lot of data, I also made a YouTube video where you can follow along by looking at the data as I'm talking about it, and by looking at a textbook graph of the energy systems used during exercise as I am explaining the concept:

Read on for the show notes.
Leave a comment.

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Show Notes for Episode 21

In this episode you will find all of the following and more:

  • 00:41  Cliff notes
  • 01: 54  Study design
  • 07:02  Changes in body weight and body composition
  • 11:57    Changes in performance (possibly confounded by the changes in body weight)
  • 14:37   The three energy systems: phosphagen (creatine phosphate), anaerobic glycolysis, oxidative phosphorylation.
  • 15:55   How these systems are affected by dietary or supplemental creatine, dietary fat, and dietary carbohydrate, and why oxidative phosphorylation can be fat-adapted (or keto-adapted) and anaerobic glycolysis cannot
  • 18:50  Aneorobic glycolosis is maximally important at 15-90 seconds of continuous high-intensity exercise.
  • 22:00  Critical performance question is how a ketogenic diet would impact ability to improve a well-trained 5-rep max (5RM) or team sports such as basketball, baseball, football, soccer, or tennis
  • 24:57  A critical health question is, how does the ketogenic diet affect cortisol, free T3, LDL-C, and sex hormones?
  • 25:56  Whether negative hormonal changes manifest is likely dependent on how full one's “stress bucket” is (a.k.a, what is the cumulative allostatic load?).

Links Relevant to Episode 21

At the request of the author, I have removed the link to the full masters thesis until the manuscript is accepted for publication in a peer-reviewed journal.

Stephan Guyenet's post, “Food Variety, Calorie Intake, and Weight Gain” discusses why any kind of food restriction will tend to produce a spontaneous decrease in calorie intake. His site is full of many other posts related to this topic.

Episode 11 of my podcast explains the role of carbohydrate in supporting thyroid and sex hormones.

The information on the energy systems in exercise comes from Modern Nutrition in Health and Disease. This is one of the few textbooks I was required to purchase in school and found so useful I kept as a cherished reference. When the most recent edition came out, I bought the Kindle version, which is incredibly easy to navigate and take notes from compared to the hardcover version I have in my office.

A Question for You

Do you have any experience with varying carbohydrate in your diet leading to an apparent effect on exercise performance? If so, based on the information I provided, would you classify the impacted exercise as dependent more on anaerobic glycolysis or more on oxidative phosphorylation?

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  1. Hi, I have been doing keto for over 3 months. It has helped my body composition and I have lost a lot of body fat. I believe because the hight fat foods are so filling, I don’t eat as much, and I am only taking in around 1200 calories a day. I am a woman at 5’3 so that may be alright. I was told my macros were 65g P, 100 get fat, and under 20g C. I am dying at Crossfit. I have completely lost all my strength.

  2. One point I think should be considered is that the LCKD group wasn’t entirely ketogenic for the duration of the study, 6 appeared to be at all measurements, 4 were at least 50% and 2 less than 50%. My limited understanding of Volek, Phinney and Attia led me to believe performance improves as people become more keto-adapted, which would make me think this study was too short to draw any conclusions.

  3. Hey Chris. Another good podcast.

    I do have a question about the need for carbohydrates to have available glycogen for anaerobic metabolism. In the case of strength training, glycogen will not be depleted THAT much. Also, from the literature I have seen, even individuals on a keto diet can replenish a decent amount of glycogen within 24 hours (cori cycle, glycerol, etc.).

    This study shows 75% with just water alone:

    Similarly, this study showed only a 36% decrease in glycogen in the muscle with a really high volume:

    I can see where carbs would be important for a highly glycogen depleting event such as MMA or a field sport, but I wouldn’t think it would be necessary for a strength or physique athlete.


    1. Hi Zach,

      I don’t think the question of how much immediate depletion of glycogen and immediate repletion of glycogen from a bout of exercise really addresses the question. The question is what happens to glycogen stores on a long-term ketogenic diet. Have you seen studies on that?


  4. Hey Chris, I enjoyed this episode, as usual. I want to bring up one thing that you mentioned towards the end, and that was that a 6-min workout like the one used in the study would be fueled primarily by fat oxidation (or aerobic glycolysis). You mentioned that anaerobic glycolysis predominates between 15-90 seconds, but I think that time would be extended in a workout like this. Assuming the participants had been properly warmed up, they easily could undertake the entire 6-7 min WOD at a RER >1.00, indicating 100% reliance on carbohydrate as a fuel. It could be assumed that much of that energy production would be anaerobic. It’s possible to be done at a lower HR and be fueled by fat, but top performers would very likely be burning carbs exclusively.


    1. Hi Jeff,

      Why do you think it would be extended? Has this been quantified in a context like this?

      Either way, would you agree that people in this study, who are not top performers, but where the requirement for inclusion is that they been doing CrossFit for one month or more, would have a major aerobic component to this workout?


      1. Hi Chris,

        This paper actually provides some nice insights, and I was a little bit off…. The people in the crossfit study were probably more likely to rely almost exclusively on carbs, whereas an elite athlete would be better at utilizing slightly more fat.

        My guess is that people in the crossfit study were similar to the ‘recreationally trained’ subjects in this study (VO2max 55 – which is quite good). The other group was well-trained (VO2max 71, which is elite albeit not quite world-class).

        6×4 min intervals (which would almost certainly be paced lower than a single 6-7 min WOD), RER in the recreationally trained group was 0.95, but as shown in fig 2 a substantial amount of time was spent at an RER over 1.0 and fat oxidation was very low. Huge effect sizes in table 4 showing the difference between an elite and recreational athlete when it comes to the fat burning.

        I’m not sure if RER or other ventilatory measures have ever been measured in the setting of a crossfit-style WOD. This would be difficult to do logistically.

        Thanks, and podcast is sounding great!

        1. Hi Jeff,

          Sorry for the late reply. I haven’t been able to look at this yet, but I saved it to a folder to look at later. Thanks!


  5. my wife and i recently had our RMR tested and we are both fat burners. She is at 92% and I am at 75%. that puts her in a Keto diet. we are both cross fitters. I know that i immediately lost body fat (while increasing my caloric intake by 1000 cals) and a week later i jumped from 191# to 200#. my starting BF was 16.2. I go back for my dexascan friday to see if my BF has changed. we have not been on this diet for long so i can not say if it has caused me to lose strength.

  6. Chris, no spinning brain today for a change! Hahaha! One thing caught my attention in particular. Are you saying that creatine supplementation could help to get you over the initial oxygen debt phase of an endurance bout? If I understood correctly, the mechanism being the CPr system being active for a longer time and thus giving the aerobic system more time to kick into action.

    1. Hi Gregor,

      That sounds very reasonable to me. I would be surprised if that made a major contribution to endurance performance that was anywhere near as powerful as training, rest, and refeeding, but I suppose for someone competing in a context where a few seconds makes a difference, maybe that could provide the competitive advantage that matters.


  7. I do a ketogenic diet during autumn and winter. I don’t eat carbs before any of my exercise sessions in the week, but eat 100-150 grams of starchy carbs before basketball games as playing well requires a lot of sprinting and jumping. Haven’t seen any evidence that people perform gylcogen-demanding activities at a good level on keto.

    Will listen to the podcast later in the week but would like to leave some thoughts on thing I’ve heard during previous episodes but disagree with.

    The idea that keto negatively affects sex hormones and decreases testosterone is a claim devoid of factual evidence. Incidents of ketogenic dieters exhibiting signs of low T is often due to UNDEREATING. Undereating also makes the thyroid sluggish. So instead of blaming keto, blame malnutrition.

    High LDL also isn’t caused by keto but often due to copper disregulation or deficiency. Deficiency of copper happens due to relying on muscle meats and avoiding liver or regular consumption of nuts or dark chocolate.

    Enjoying the podcasts but as for the claims about keto then its like a second hand tooth brush, I ain’t buying it…

    1. Hi Abu,

      I think where you’re going wrong is proposing these are either-or questions. Pretty much everything in biology once the hypotheses are narrowed down to what’s reasonable becomes a both-and question where context is the overwhelming determinant. That is definitely the case here.


      1. Thanks for the reply Chris.

        I agree that certain individuals may experience decreased sex hormones on keto but do you think this can happen on a VLCD where caloric intake is adequate. I can’t enumerate the amount of people who restrict carbs and keep their protein moderate while only eating around 100 grams of fat, thinking this is enough to keep their metobolism in check. If I can see some evidence of low T in individuals who are not callorie restricted then I may be more convinced of your opinion on this. Many who can benefit from keto may be reluctant to give it a go because of these sorts of claims.

        I have great respect for the work of you and Chris Kresser but feel some of your views on ketogenic diets aren’t that sound. There seems to be a vast difference between what low carb experts like Phinney and Volek advocate and what people actually follow.

        1. Hi Abu,

          My comments were not based on anecdotes. They were based on the physiology of insulin and the results of clinical trials showing effects of low-carb diets on thyroid hormones.


  8. When you are in ketosis, are the myocytes using FFAs primarily to run Krebs ( and then ketones as extra fuel ), thereby saving the limited glucose and whatever ketones the live makes for the brain?

    1. Hi Newbie,

      It has been a while since I studied this, so I wouldn’t take my word as the last word, but from what I remember muscles initially use fatty acids and transition to ketones with time as ketogenesis becomes stronger and the body adapts to using ketones.


  9. Excellent information for us.. I am very interested in this concept and you give us what we need without trying to sell us a bunch of stuff as so many do on other websites.. Brovo!! Thank you so much

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