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:
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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?