CrossFit South Rockland

Monday, January 22, 2018

Should You Do CrossFit on a Ketogenic Diet?

Transcript of Episode 21

This transcript was generously provided by Cassandra Barns.

This is Chris Masterjohn and you’re listening to episode 21 of Mastering Nutrition.

Alright folks, today we are talking about “Should I do CrossFit on a ketogenic diet?”. And the cliff notes are as follows.

00:41 Cliff notes

If you do CrossFit on a ketogenic diet, you may lose weight. You won’t die. But, you probably won’t sacrifice your performance on the metabolic conditioning workout of the day, or WAD. But I wouldn’t be so sure that you are not going to your sacrifice your performance on strength-based training. And that’s because the study that we’re going to look at today did find that you won’t sacrifice your performance on a four time workout lasting 6 to 7 minutes, but I would not expect carbohydrate restriction to have a major effect on that type of exercise, and I would expect it to have a potentially major effect on, say, a set of 5 to 8 reps in weightlifting, on sports performance in things like baseball, football, basketball, soccer, tennis, racquetball, and so on.

Alright, that’s the cliff notes. Now let’s dive into the full topic.

Several people on Twitter independently at different times asked me to respond to this study.

01:54 Study design

And this study is from Rachel M Gregory. It’s her Master’s thesis at James Madison University, and it just came out in spring 2016, and it’s called “A low-carbohydrate ketogenic diet combined with six weeks of CrossFit training improves body composition and performance.” I think the title is slightly misleading. It should say that CrossFit improves your CrossFit performance, and that a ketogenic diet does not hurt your improvements, because that’s what the study actually showed. But I would definitely not say that the author is trying to misrepresent anything in here. I think that, you know, having read the entire Master’s thesis, I think that what she’s trying to say is as follows. A lot of people are trying to lose weight, a lot of people are trying to get fit, but they’re having trouble because they don’t like to stick to the diets and a lot of the exercise that they’re trying to do is boring. In CrossFit you get a community where – and maybe to differing degrees depending on the box, but in general one of the things you get at CrossFit is a social support network that encourages you to get fit and maybe to lose weight in some cases. And again, an exercise program that’s varied enough to not be as boring as some other programs. And with a ketogenic diet you get a diet that is filling, leaves you feeling energetic and helps you lose weight. I do think that there is a little bit of a bias towards praising the superiority of the ketogenic diet compared to other weight loss diets – it’s probably undue. But I’ll leave you to read the Master’s thesis if you’d like, and I’ll link to it in the show notes, and assuming that it stays available at the local CrossFit site that published on their website, then you will be able to read that.

But what – I want to focus on what are really the main points here. So, what they did in this study was they took people at Rocktown CrossFit who had been doing CrossFit for at least one month prior to the study, and they randomized them to two groups. In the control group, they kept doing CrossFit for six weeks and kept eating whatever they were eating. In the experimental group or the low-carbohydrate ketogenic diet group, they ate a ketogenic diet. I think most or all of you listening know what a ketogenic diet is – briefly, in this case what they were doing was dropping the carbohydrate content down to very low levels – around 50 grams or less per day in order to force the body to burn mostly fat for energy. And so in both groups they kept doing their normal CrossFit routine for six weeks, and they did a performance test at the beginning of the study and then at the end of the study, to see if the diet affected the performance. The performance test was mostly bodyweight exercises. It started with a 500 meter row, which is not a bodyweight exercise, but then it went on to a series of exercises that were bodyweight exercises. And these included 40 bodyweight squats, 30 abmat situps, 20 hand release push-ups, and 10 pull-ups. Now, I want to point out here, and kind of put a mental pin in this – when you are doing bodyweight exercises, you’re doing more work if you weigh more, and you’re doing less work if you weigh less. So if you had zero change in true performance, like in true strength, then on bodyweight exercises, you should still be able to do more of them if you lose weight. Not because you got better at them, but because you’re doing less work when you’re pushing less weight around. And although I wouldn’t call the 500 meter row a bodyweight exercise, there was only one measure of performance because the measure was how long – how many seconds does it take you, or how many minutes but it was reported in seconds, to do this entire sequence of a 500 meter row, 40 bodyweight squats, 30 abmat situps, 20 hand release push-ups and 10 pull-ups. And so what that means is that that’s overwhelmingly – that’s one measurement that’s overwhelmingly determined by bodyweight. And therefore, you should expect a group that lost more weight to – with the same performance – have better – with the same amount of strength and the same amount of speed and whatever else, they should be able to do more of that or to do the same workout in less time, because they weigh less.

07:02 Changes in body weight and body composition

Okay, now let’s switch gears and look at what happened to body weight, and what happened to performance. So the short of it is that the ketogenic diet group lost weight, lost BMI, lost percent body fat, lost fat mass, and they had slightly lower lean mass but it was not statistically significant, and I wouldn’t even call it meaningful in my view. The lean mass loss was about 0.3 kg, which is a little under a pound, and the weight loss was about 7 pounds or so. And so that’s – and that is an extraordinarily – even if you assume that that’s a true loss in lean mass, despite no statistical significance, one seventh of the weight lost as lean mass is really low.

Now, that’s not surprising because these people were doing CrossFit. So the number one thing that preserves lean mass during a caloric deficit is resistance exercise that provides an anabolic stimulus, that in the in the context of a hypercaloric, protein-adequate diet would cause you to gain lean mass, but in the context of a hypocaloric protein-adequate diet, what it causes is you to preserve lean mass. So that has everything to do with the CrossFit, and I doubt has anything to do with the ketogenic diet. It’s just the fact that this was not a high-risk situation for lean mass loss, because they were weight training four days a week. And then, you know, after that the number two determinant is protein intake. And on a ketogenic diet, you know, sometimes you restrict protein, but they were eating plenty of protein on this diet. I believe – I believe they were actually eating – let’s see here, they were eating about 80 to 100 g a day for protein and that was – well it wasn’t statistically significantly greater than the control group, but it tended to be a little bit greater. So in any case, they were not restricting protein on this diet and so again, that would not put them at risk of loss of lean mass. So nothing surprising there.

Now, the control group did not lose any weight, BMI, percent body fat, or fat mass. And why would that be? Well, I think that can easily be seen by looking at the calorie intake. So in the control group they started around 1800 calories a day, and they pretty much maintained that throughout the study – there’s a slight dip to 1600 calories at week 4, but the beginning of the diet, week 2, week 6, pretty much straight 1800 calories a day. Now by contrast, in the ketogenic diet group they started out at almost 1900 calories a day, and then by week 2 they were eating 1800 calories per day, and by week 4 and 6 they were eating a little under 1500 calories a day. So it is – I mean, who on earth would be surprised that you subtract 300 to 400 calories a day and you wind up losing one pound a week. I mean, that’s as conventional as it gets.

So at the end of the day, what you see here is that the ketogenic diet like, you know, a Paleo diet, a vegan diet, a low-fat diet, a low-carb diet, a Zone diet, an Atkins diet, a South Beach diet – any restrictive diet makes you more conscious of what you’re eating and has – Stephan Guyenet has documented extensively over at Whole Health Source, any restriction in your dietary variety is going to convince your brain that there is less reward in eating that food, and induce a caloric deficit in that way. So, you know, I think what this is showing is that the ketogenic diet is one of many ways that you could lose weight. And in the context of CrossFit, as long as you don’t restrict dietary protein as part of the diet, you will not lose a significant amount of lean mass as long as you keep your weight loss to a rate of a pound per week. And I think in the overall – sort of – what seems to be the overall goal in reading this Master’s thesis, I think that was really the point, was to say look, this is one of the options for the average Joe that can provide good results.

11:57 Changes in performance (possibly confounded by the changes in body weight)

Now if you look at the performance, what you basically see is that in this CrossFit workout that’s based on the row and on the bodyweight exercises that I mentioned before, it was basically in the range of 6 to 7 minutes, where they were starting out closer to 7 minutes and then over the course of the study, the goal was, let’s try to get this 7 minutes down to around 6 minutes. And so what you see is that both groups lost a little under a minute in the time it took them to do those exercises. In the control group it was 41 seconds, in the ketogenic diet group it was 55 seconds. The difference between the groups was not statistically significant. Now, you could argue that there is 14 seconds difference – maybe the variation in performance was too large, the sample size – 12 people in the ketogenic diet group, 15 people in the control group – was two small. But, you know, we don’t know the answer to that. So, like I said before, you should expect that if the ketogenic diet group lost 7 pounds of weight, they should do better on the performance improvement, not because they actually improved their performance, but because they’re doing less work during that workout. And so maybe that is what we see, and maybe that is what that 14 second gap is between the groups and we just don’t have the statistical power to really answer that question. But I think, you know, it doesn’t really matter that much, because someone who is a competitive athlete who’s trying to sha… where every second you can shave off the workout counts, is going to care about this, but again, this study is kind of geared more towards, is this a valid option for the average Joe who wants a fun way with community support to lose weight and get fit? And in that sense I don’t think that most of these people are going to care that much whether changes in the diet are going to lead to a 5 or 10 or 15 second difference in this case.

Now I want to switch gears and talk about why I don’t really think that this is getting to the heart of the matter in terms of what I would expect to compromise performance. And to really get into that, what we need to do is talk about why carbohydrate is important to performance.

14:37 The three energy systems: phosphagen (creatine phosphate), anaerobic glycolysis, oxidative phosphorylation.

And that requires talking about the three energy systems that are contributing to the work that your muscles can do during exercise. The first system is creatine, or the creatine phosphate or phosphagen system. And that is overwhelmingly what you’re using in the first 15 seconds of exercise. Its contribution drops to about 25% of energy between 15 and 90 seconds, and then after that it just becomes increasingly irrelevant. Your second system is anaerobic glycolysis. And that is negligible in the first 15 seconds, but it becomes really important in 15 to 90 seconds, and then still makes a substantial contribution for the rest of, say, the first 30 minutes; but then after 30 minutes its contribution progressively declines. And then oxidative phosphorylation begins pretty much irrelevant, and then kind of starts creeping up in the first 90 seconds, but it’s really becoming significant after 90 seconds; and then by 30 minutes it’s becoming overwhelmingly the dominant energy system.

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

So from a perspective of diet, why are these important? Well, the creatine system is not really going to be affected by fat or carbohydrate in the diet. The creatine system is going to be affected by your endogenous creatine synthesis, and it’s going to be affected by the creatine in your diet, which is coming from animal flesh or creatine supplements. And if you think about creatine supplements used to build strength or lean body mass, what you’re essentially trying to do there is push the boundary of how long you can use that creatine beyond that 15 seconds. So if you can use that creatine is a substantial energy source into 90 seconds, for example, you know, that’s really going to help you lift weights. When you’re thinking about weight sets that are, say, 5 to 8 or 10 or 12 reps, because those sets are taking you into that 30, 45, 60 maybe 90 second range. And if you think about the importance of anaerobic glycolysis, its importance is that you can only use carbohydrate to support that system. And if you look at where that becomes dominant, it’s in the 15 to 90 second range. And again, if you think about CrossFit, that’s – where you’re really getting into that is in your, you know, 5 rep, 8 rep, 10 rep squat or deadlift or bench press. Because those 5, 8, 10, 12 rep sets are what is taking you 30, 45, 60, 90 seconds.

Now, if you think about oxidative phosphorylation, its significance for the diet is that it’s the most flexible out of all of these. So you can fuel that with fat, with protein, with carbohydrate. And if you are on a mixed diet, that oxidative phosphorylation is going to be probably largely fuelled by carbohydrate, you know, through beyond 30 minutes, especially when you’re exercising at higher intensities. So if you’re exercising at, say, 60 or 85% of your maximum oxygen consumption – your VO2 max – for 30 or 60 minutes, you’re going to be relying on a lot of carbohydrate during that time. But that’s where the concept of fat adaptation or keto adaptation becomes important, because you are dealing with oxidative phosphorylation at those time points, and because that system can be fuelled by carbohydrate or fat or protein, it’s very flexible, and that’s the energy system that can get keto adapted or fat adapted.

18:50 Aneorobic glycolosis is maximally important at 15-90 seconds of continuous high-intensity exercise.

Now the problem is, why is it the case that anaerobic glycolysis is so important in the 15 to 90 second mark? It’s because it does not require oxygen. And at the 15 second mark, you’ve run out of a lot of your creatine, but you have not yet been able to infuse the maximal amount of oxygen into that tissue. And so you wind up with a gap between the ATP that your muscle is blowing through and the amount of oxygen available to produce more ATP through the most efficient mechanism the cell has, which is oxidative phosphorylation. And so, when that happens there is a lag where your nervous system needs to coordinate a response that involves increased breathing, increased heart rate, taking the oxygen from the breathing through, you know, more dilated blood vessels pumping it at a greater rate into the muscle tissue, perfusing the tissue, delivering the oxygen and then equilibrating the mitochondria in the muscle cell up to that newer level of oxygen that’s needed. So all of that takes a minute or two to happen. And keto adaptation or fat adaptation doesn’t have anything to do with that process. What it’s doing primarily – to my understanding anyway – is increasing at the cellular level at the muscle tissue, increasing the ability to use ketones for energy. That’s not going to make that system of delivering oxygen to the tissue happen more quickly. So this dependence on carbohydrate at 15 to 90 seconds, your best bet to try to diminish a carbohydrate dependency there is not to fat adapt or keto adapt, it’s to try to stuff more creatine in the muscle, and that’s exactly why bodybuilders and strength trainers often supplement with creatine.

And so what I would be concerned about for performance in a carbohydrate-restricted diet is maximal peak performance in exercises that last 15 to 90 seconds. In the study that we were talking about, they were trying to get a 7-minute workout down to a 6-minute workout. Fat adaptation is going to be very influential on that kind of workout. And anaerobic glycolysis that is dominating at 15 to 90 seconds is not going to be the major driver of your performance in such a workout. So what I would’ve been much more interested in seeing from – and I’m not saying they asked the wrong question, I’m just saying the question that I would want answered from the perspective of a ketogenic diet impact on athletic performance in the context of CrossFit is, what about their 5-rep max?

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

If you take someone who’s trained for a few years, who has a very well-established 5RM, and you take a pool of those people and you randomize them to two different diets and the goal over the 4 to 6 to 8, probably 8 week cycle is, can I take my well-established 5RM and take it to a new level – a new personal record or PR. And I would want to see, does the ketogenic diet impact the ability of that well-trained 5RM to reach a new PR. That is where I would be concerned about the potential for the ketogenic diet to impact performance. Take this outside of CrossFit, where else would you see this? Well I think if you look at basketball, you look at football, you look at soccer, you look at tennis, you look at racquetball, you look at baseball, most competitive sports outside of, say, marathon running, endurance cycling; most team sports – and most competitive sports in general – that have wide followings that people watch on TV, that people routinely do for recreation – I think that if you look at those sports you overwhelmingly see a dependence on peak performance needed for bouts lasting less than 90 seconds. And the other area then that I would want to see performance assessed would be, how does this impact performance in these sports that are so dependent on these short bursts of energy. And, yeah, you know, you don’t want to be crashing in the middle of a game, and, you know, I say this as someone who is not a professional sports player, who’s not very good at any of those sports, who doesn’t – you know, like, and I’m not even an exercise scientist, right? So this is peripheral to my expertise, my expertise is in nutrition. But clearly there’s an intersection with my expertise and sports science. And so I’m not going to pretend to have the last word on this, but as far as I can tell, to the best of my knowledge and understanding, just by watching a game of basketball, you are frequently operating in short bursts of energy that I would expect to be carbohydrate-dependent, and that I would not expect fat adaptation or keto adaptation to solve, because they’re operating in that range where you just can’t keto adapt or fat adapt the way that the heart rate and breathing rate and blood supply is adjusting to those short bursts of energy located at the muscle.

24:57 A critical health question is, how does the ketogenic diet affect cortisol, free T3, LDL-C, and sex hormones?

Alright, I’ll add one last thing. And that is that… I’m going to add two last things, actually. The first is that I also want to see what is happening to these people’s thyroid hormone, to their cortisol, to their cholesterol, to their sex hormones. And that’s because where I become concerned about the risk of chronic carbohydrate restriction is in losing the insulin stimulus as a signal of short-term energy status to support the antioxidant defense system, to support fertility, largely through governing thyroid hormone. And I’m not going to go into that in detail here because I went into detail in episode 11 of this podcast. You can find that at But I will say here just to follow through, that I think that whether someone experiences poor thyroid function and a drop in sex hormones is going to be very individualized, and is going to depend on how many stresses are in that person’s stress bucket.

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?).

So I would say carbohydrate restriction is a stress, fasting is a stress, weight loss is a stress, exercise is a stress, work goals are a stress, dealing with family matters are a stress, pregnancy is a stress; there are many things that are stressors. And they can be good or bad, depending on how we react to them and what our reserves to deal with them are. And so although each stressor involves different sets of responses, to some degree they are overlapping, and to that extent we can intuitively understand this as having a single stress bucket, and that stress bucket will have, you know, all those stressors going into it, and the fuller that stress bucket gets with the additive effect of all the different stressors, the less we can tolerate additional stress. And so I think for someone whose stress bucket is relatively low, they can put a low-carbohydrate ketogenic diet into that stress bucket and there’s plenty of room for that particular stressor. And maybe that creates a positive adaptation in that person. Now I’m sceptical that that someone should, without a good therapeutic purpose behind it, stay on a ketogenic diet long term, always and forever. But certainly over the course of six weeks, the question is, how full is your stress bucket? So, again, I’ll direct you to for a much more elaborate discussion of that concept.

And I would conclude from this that the ketogenic diet is a potential route to weight loss in the context of CrossFit, where you have a very strong resistance program that’s going to provide an anabolic stimulus to the muscles, and you’re keeping any potential weight loss to a pound a week, it doesn’t seem to be a risk for lean mass loss, it doesn’t seem to be a risk for performance in terms of a metabolic conditioning WAD lasting 6 to 7 minutes. There may be a slight increase or decrease with performance that this study couldn’t detect, but it doesn’t seem to be very large, and for the average person doing CrossFit I don’t think it’s very meaningful. But I’m not so sure that it’s not going to hurt your ability to reach a new 5RM or a new 8RM on the weightlifting workouts. And I’m not so sure that it isn’t going to hurt your peak performance in the types of sports that I was talking about before. And I would – if I had to choose one or the other I would lean towards the position that it’s probably going to hurt your performance on those particular types of things, or at least that is where the greatest risk would lie for performance. And I think it’s important if you’re going to do a ketogenic diet that you first ask why. Because yes, this study shows and corroborates other evidence that it is a path to weight loss. But there are many paths to weight loss and they’re – probably the bulk of them are easier than the ketogenic diet, simply because they are less restrictive. And so I think that you want to ask the question, why am I on a ketogenic diet? There are good reasons to go on a ketogenic diet but that doesn’t mean that everyone should be on one. And I think you want to, you know, carefully look at your body’s response. And this is not just about a ketogenic diet, this is true about everything, but in particular what I would be concerned with measuring your response to on a ketogenic diet long-term would be those things I mentioned before. Low T3 or low free T3, high cortisol, high LDL cholesterol, low sex hormones. If you see three or four of those in a pattern, that to me means you probably could benefit and greater protect your long-term health if you were to increase the carbohydrate content of your diet.

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