Episode 423: Is Low Carb Back? New Study Sheds Light
A recent study was recently published by Prins, Noakes, Koutnik, et al. that examined the role of stable blood sugar through very small carbohydrate intake as the main determiner of performance for endurance athletes, as well as some insights into low carbohydrate performance compared to high carbohydrate. I take a look, and share some thoughts.
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Timestamps:
00:00:00 Low Carbohydrate Diets for Endurance Athletes
00:03:10 Debating Glycogen's Role in Endurance Performance
00:06:36 Nutrition Strategies for 100-Mile Races
00:09:45 Ketogenic Diet Study on Triathletes
00:12:55 Ketogenic vs. High Carb: Performance Impacts
00:16:29 Optimizing Carbohydrate Intake for Athletic Performance
00:19:49 Impacts of Ketogenic Diet on Endurance Performance
00:23:17 High vs. Low Carbohydrate Runners: Impact on Performance
00:26:15 Understanding Race Intensity and Duration
Episode Transcript:
Alright, everybody. This is going to be one of the shorter episodes that I do solo that I'm going to add more of to the podcast this year. For this specific one, I want to dive into a recent study that just came out on low carbohydrate endurance. So, you know, it's been making the rounds on the internet. You're seeing a lot of chatter around kind of whether it means anything, whether it proves low carbohydrate diets are applicable for endurance athletes, on par with high carbohydrate diets. And, you know, push back from the other side saying, like, this doesn't answer any of those questions. Those are kind of the extreme versions of it. There's also a lot of middle ground out there if you look for it, too. And I think it's just interesting the way it was constructed and some maybe takeaways. So I want to chat about it a little bit. I'm not going to dive into it super deep to the degree where we're like going through the study and picking out specific pieces of it to a large degree. I'll highlight some of that stuff just so you have some background information. But if you really want to dive into this study itself, either go to the study, which I will link to the show notes, or maybe even better yet, check out some of the stuff that Brady Homer has put out on it, either on his Substack or his Instagram page. I think Brady has broken it down in about as unbiased a way as you possibly could. Something like this. And comes at it with just a sense of curiosity, but also a sense of skepticism by including what he knows about kind of endurance, physiology and nutrition and all that stuff, too. So if you kind of want to get an overview of just some of the nuts and bolts of it and dive in a little bit deeper, definitely check out his Substack and his Instagram. I'll link both of those in the show notes as well, so you can click over to those if you want to head over there while you're listening to this or after to kind of check out some of that stuff. But the interesting thing about this study, and it kind of had some inklings of this sort of a study coming out, because over the last year or so, I know Tim Noakes specifically has been talking quite a bit online about how there is really no confirmed evidence that I shouldn't say. There's no clear confirmation that one of the limiters to endurance performance is stored liver or muscle glycogen, essentially. The way that we've thought about this and theorized to date, is that one of the goals of an endurance athlete, regardless what your diet is going to be, is to defend your liver and muscle glycogen, because when those supplies, those pools start dipping below a certain point, your body starts to try to course correct by lowering your output or making your effort more difficult. So you're less likely to continue to tap into that. So you sort of have this situation where if you go out on a run or a race, your body is going to be burning some percentage of fats and some percentage of carbohydrates. Diet and training, stimulus and lifestyle and things will impact how those numbers play out. We'll talk a little bit about that. but, you know, regardless, you're going to find yourself in a spot where you're going to be dipping into that small pool of fuel from glycogen stores. And over time, if you don't take in a carbohydrate that will be preferentially burned, your body will be dipping into those pools to the point where your body starts sending those signals of, okay, make this more difficult. Make that pace more difficult for the person to produce in order to preserve that. So that is kind of one of the things that this study is sort of challenging is, is that the real limiter that we're seeing, or is it what Noakes has been talking about a little bit more just defending blood sugar levels, meaning like trying to stave off this, this hypoglycemic state where you have a dip in blood sugar and that is what is driving the. Increased perceived effort at a given pace. So if he's right or if they're right, then you have this scenario where the goal would be targeting stable blood sugar versus trying to build your fueling strategy in a way that would defend liver and muscle glycogen, the way that we've sort of looked at it historically. So disclaimer here, I mean, for me, all my racing to date from the start of being on a low carbohydrate to today has been in line with that theory that liver muscle, glycogen defense is what I need to do. And I've built up my fueling strategy to accommodate that. So if you look at my metabolic cart testing, you know, I know at like my 100 mile intensity, I'm going to be burning somewhere between 80 to 90% fat, and then the remainder will be carbohydrate. So when I build up my fueling strategy, one of the reasons why I'll target roughly 40g of carbohydrate per hour on on many of those races is because I'm trying to defend or introduce enough carbohydrate over the course of that roughly 12 hours to make up for what would need to be dipped into that liver muscle glycogen, and then therefore keeping that intact so that I don't feel that as much of that increased effort along the way. Now, there's other things at play. Obviously, when you're running and racing that is going to kind of increase fatigue, but that's one to be considered about and want to try to figure out for yourself. So that's how I've built my things out. That's how I've raced. Um, when I have done races, hundred mile races going lower than that, I have had harder races. I haven't had as good a finish as I felt like I, you know, was a lot flatter at the end of the race than I was during it, in the middle of it, starting it and all that sort of stuff. And I've also done races where I've introduced more and I haven't perceived any improved or increased benefit from that. So for me, my anecdotal race experience tells me that based on my dietary habits, lifestyle fueling targets. That kind of 40 gram number is what really, really works for me. So you're going to see a lot of range there. I mean, especially in the ultrarunning world, cycling world, racing world in general now, where athletes are targeting very, very high numbers and sometimes up well above 100g per hour. And they're sort of following a similar equation as I am. They're just building it off of the framework that they're getting from their testing. So if they're a high carbohydrate athlete, they're probably more likely to be something closer to 5050 carbohydrate to fat metabolism when they're at their like, say, 100 mile intensity. So for someone who is running near the front of a pack, you know their workload may be high enough to where that could necessitate, you know, 100 plus grams of carbohydrate to defend that. So that's where you get that disparity between my target and their target. But we're kind of working from the same equation. So this study is sort of challenging some of that in terms of like, do we need to work off that equation, or should we be just introducing enough glucose into the bloodstream to maintain those levels? Some other things that this study actually looked at too is can a low carb athlete perform just as well as a high carb athlete after proper adaptations, meaning they've put the diet into practice long enough, where we can safely assume that they've made those adaptations to the degree where they can rely on fat as a primary fuel source at certainly these lower intensities, but further along that intensity spectrum or in the in the endurance world. So they kind of look at that too, just by sort of default by the way they structured the diet. Yeah. So that's kind of like the stuff they're kind of taking a look at in there. The other thing I guess you could maybe consider pulling out of that is in terms of a target they're looking at is like, what is this minimal carbon take during exercise. Do it for endurance. I kind of challenged that whole thing like, we should be pushing these 100 plus grams. So to some degree, I think they're challenging, whether even the moderate to high carbohydrate athletes would need to be doing anything near what they're currently practicing. So that's kind of like the background of it. So let's jump in. I'll share just before we get going, and I'll link this in the show notes as well as the study itself is titled carbohydrate ingestion eliminates hypoglycemia and improves endurance. Exercise performance in triathletes adapted to very low and high carbohydrate caloric diets. So basically kind of what I was saying before, it's kind of challenging that theory that we should be targeting defense of liver and muscle glycogen, but rather, you know, your blood sugar is what they want to be targeting there. The way they set this study up was actually really interesting. So they took a group of triathletes. And essentially what they did is they put them on a six week phase where they were doing a pretty strict ketogenic diet, actually giving their lifestyle. I would safely say this is a ketogenic diet. They were at most taking in 50g of carbohydrates per day. So they're going to be in a state of ketosis. And I believe the blood markers that they produced over the course of that were up into that just above 0.5 million goal range, slightly above that, which isn't uncommon. We learned from the faster study that you can produce insanely high fat oxidation rates. Just barely in that kind of therapeutic ketogenic range of 0.5 and above. So that doesn't surprise me that they weren't putting up like these massive numbers, like three millimeters or something like that. There may be something with athletes that kind of controls for some of that, uh, that higher ketone range, uh, with lifestyle impacts. But we know that their fat oxidation rates are through the charts. In fact, in my mind it was 1.56g per minute. My blood ketones and during the faster study ranged from 0.4 to 0.7 millimeters. There were folks in the faster study that had higher fat oxidation rates than I did, and they weren't producing like these massive blood ketone levels either. So I think that's just maybe just something to consider when you're deciding, like, what should I measure? How much weight should I put behind some minimal score and things like that? From what this study would show, what the faster study would show with the data that I have on myself, would show, is that that number isn't necessarily always going to be indicative of your quality of fat oxidation rates. So if you're looking for high fat oxidation rates in order to potentially have a lower fueling demand during your race, then you probably don't need to be chasing these sky high ketone levels. The interesting thing they did is after that six week phase on the low carbohydrate diet or ketogenic diet, they did a two week washout and then followed with a high carbohydrate. And they did it in a way where like the six weeks on the high carb was going to be noticeably different from a carbohydrate standpoint, but the calorie intake was similar, so that we didn't have an issue there. Uh, I believe the six week high carb diet was somewhere around 380g of carbs per day. So pretty big difference between, I think, what would that be like 7 or 8 times the carbohydrate intake of the ketogenic group and. What they did is they tested them. So they tested them with low carb with a placebo. So they had a solution that just had no carbohydrates in it. And they did low carb with ten grams per hour that they spaced out with about 3.5g every 20 minutes. In a solution, I assume the solution pretty much tasted the same, or was similar enough where the participants were like, had no clue whether they were getting the no carb or the ten gram per hour carb. And then the high carb group, they did the same thing with a placebo, and then with the ten grams per hour in that 3.5g every 20 minute kind of framework. So what came out of this was that when, uh, when they had no carbs in there, so when they did the placebo, the performance difference was non-significant between the ketogenic and the high carb participants. So their time to exhaustion that they had that the test they used was a 70% VO2 max there. There wasn't anything meaningful or significant in the data difference between the keto group and the high carb group. So they're looking at that as like, okay, is this evidence that there's no actual performance deficit when there is an adaptation phase, in this case, six weeks off to that diet versus what we've maybe seen in prior studies where they don't have that long of an adaptation phase. And this would suggest that maybe there isn't. Um, I still have questions about how this actually applies in the real world, that I'll talk about a little bit when I get to kind of some of my takeaways. And there's also worth noting significance in these studies doesn't necessarily mean it was equal to the decimal point. It usually just means it wasn't enough for them to fall outside the margins. So there was a slight, I think it was just a few minutes further that the high carb did. So if we were able to like Grant, that measurement was precise enough. You could argue that, okay, maybe it's not significant in laboratory settings, but if you're talking about real world race settings where we're dealing sometimes with seconds, you know, a couple minutes could make a big difference. So worth noting. The interesting thing, though, is once they added that ten grams per hour and those 3.5 every 20 minute doses, they had a pretty big improvement in time to exhaustion with that 70% VO2 max test, and it was 25 minutes longer for the low carb group and 12 minutes longer in the high carb group. So we saw both groups improve with that introduction of carbohydrates. So that kind of maybe tells us a few things. One is maintaining that blood sugar level does seem to help improve performance, and also some ingestion of carbohydrate seems even minimal in this case seems to improve performance. Not necessarily things we didn't necessarily know, but interesting just to kind of have that confirmation. I think especially with that ketogenic group, because one thing that I've always been curious about is just like, you know, when someone decides to do a ketogenic diet or a low carb diet, what should their race strategy be? Or what should they kind of build that around? Should they try to do a race, especially if they're a strict ketogenic diet individual? Should they be trying to do races without introducing carbohydrate, or is a small amount something that's worth their time and energy to include? So we did see that increase. Uh, what we don't really know from this study, or can't really tease out from this study, is would we see an even better performance if we did say 20g? And is there like an increasing improvement by these ten grand increments? And at what point do we start not seeing that improvement any longer? I think that maybe answers some questions like, do we need to be doing these really hyper high carbohydrate fueling strategies versus the total opposite of this, basically at ten grams per hour? Or is there like some middle ground in there where you kind of hit this sweet spot where going above it really isn't going to improve you very much. And then you also introduce the logistics and the potential digestive issues that have come around. Come along with that increased fueling demand. So. That I think is maybe left a little bit out in the open from this study. You can maybe combine other things to kind of grasp some of that stuff, but some takeaways I kind of had from this was, uh, what about time? I always think about this one when we see these studies. I thought about this one when we did that faster study. I thought about this one when the more recent study came out a couple of years ago, where they looked at runners, I think the runners were like middle aged men that were training at like, you know, a fairly typical framework that you would maybe see someone that is out there, you know, training for like or their weekend races and things like that. So not elites, but also not kind of just like hobbyists either. They were pretty focused training, and that one showed that there was no difference between the low carb and the high carb groups with some higher intensity intervals. You know, my question with that one was, okay, well, let's apply that to more than one workout per week for a few weeks and see if that continues versus this one single test. And the reason I always ask that is because from my own experiences, even if I go on a like pretty strict ketogenic diet and then go out and do like one short interval session, I can often match the demands that I were able to that I that I was able to do when I was more high carbohydrate. For that one session. But if I continue to do those, I start to notice that I have a depreciation. So I'm always curious about what happens when we reapply this for a very specific, typical endurance training program where you might be doing a couple quality sessions from a speed work standpoint in the long run, and kind of all those ins and outs that go into it. So this study really didn't answer that as far as, as far as I can tell. So my question is always still, what about time? How does that impact the reduction in carbohydrate? The other thing that I'm curious about here is like why can it be both? Why can't it be a scenario where maintaining proper blood glucose is important in keeping perceived effort in check, but also the reduction in glycogen stores essentially. So could it be that, like you want to have well-defended glycogen stores but also maintain good blood sugar levels? And if either of those get compromised, you're going to see a deficit in performance or the other way to look at it. If you keep both of those optimized, you end up having kind of a good scenario where you're feeling strong and well, fueled by the end of the race and not fading due to energy input type stuff. So that's what I hope maybe gets teased out with some future studies and things like that. Let's look at just how long does this process of improved performance actually continue at that ten gram dosage per hour and wherever that ends? How much further, if at all, can you do it by increasing that? Because at the end of the day, for me personally, if I want to look at this very selfishly, I'm not racing for, you know, time to exhaustion in like the two hour framework. Um, I'm running to exhaustion for 11 or 12 hours on a flat, controllable 100 miles. So I always want to know, like, well, how does this kind of extrapolate out? Can we extrapolate out or something going to change over those times? Also, the other thing that I take away is like, do we really know that? Glycogen levels were adequately lower with that low carbohydrate group, because one of the things that this study uses to sort of show what they're trying to show or what what some people are trying to represent it as, is that if this ketogenic group improves performance by maintaining blood sugar, we can assume that that is the driver. On reducing perceived effort with carbohydrate intake versus defending liver muscle glycogen, because we should just assume that a ketogenic athlete is going to arrive to that task or that race with lower liver muscle glycogen, meaning they're already kind of maybe at that point where we would start seeing, you know, compromised performance if that person were on a moderate to high carbohydrate diet. And I'm not entirely sure that's the case. I think what we know or we think we know is that if you go on a ketogenic diet, you're likely going to see an initial drop in that where your liver muscle glycogen stores are going to be lower than they were before. But over time, as you adapt, your body accommodates a lot of that by just increasing your fat oxidation rate. So more of your energy is used from fatty acids than it was from carbohydrates anymore. And. I believe if we extrapolate out far enough, some of that even normalizes to a degree to where you're not going to have the same carrying capacity and liver or muscle glycogen as someone who's just testing those nonstop with the high carbohydrate inputs. But I think there is a normalization where it doesn't stay as low as it originally did. So if we don't actually test that before a study like this, we don't necessarily know how low or how much under they were, and whether we can maybe make that assumption that they would be experiencing some sort of a performance deficit due to low liver muscle glycogen, just for some actual data, too. I mean, the faster study, despite being on a ketogenic diet, the athletes muscle glycogen utilization and depletion patterns during and after exercise were similar to those on a high carbohydrate diet. So this does kind of suggest that even with lower carbohydrate intake, glycogen stores in the muscles are not necessarily depleted more than the high carb adapted athletes during similar exercise bouts. So it doesn't mean they need to go in with a lower price. It just meant over the course of the exercise stimulus that was being tested, they didn't like. A difference in terms of what that effort did to their remaining stores. So, you know, to some degree that would maybe make sense, because if you're a high carbohydrate runner, you can just assume you're going to be burning more carbohydrates at any given intensity than the low carb ketogenic folks will be. So then you know where you start and where you end can be impacted by that just as much as it can be your starting point. So that's kind of some of my takeaways there too. So this is all new. I'm just kind of thinking out loud to a large degree with this based on some of the topics I've seen discussed online reading Brady stuff, uh, looking at the study myself. But there's probably some things that I've maybe missed in here that I want to try to learn. So perhaps I'll do a longer form guest interview in the future with someone who can speak a little more detail to it. What I do think is interesting here, though, is a lot of times with these things, when we start actually getting into discussions and debates online about them, is we try to look at them through the lens of these elite athletes. And to some degree, that makes sense because these folks have a lot more testing done on them. So we just have more precise information. But to the degree that that's applicable to the average person who's going out there training for an ultramarathon or a road race or something like that, you know, it's going to vary a lot. So I always kind of like to remind people like, first of all, when you hear about the pro ketogenic diet, crowds talk about how its benefits are here or here and there. And then you also hear people say, if you're an endurance athlete, you should never entertain a low carb ketogenic diet. Take both of those with a grain of salt, because most of the time, both of those groups, they're telling you all the benefits of one side and none of the downsides. And they're also telling you all of the downsides of the other and very few or any of the upsides. So you don't necessarily always get the same kind of what I would say, at least a non-biased kind of glance at this. The way that, like someone like Brady is going to do, do for you. So keep that in mind when you're looking at this stuff and then also take your own individual goals and, uh, and, and kind of benchmarks into mind to where, you know. One thing I always like to ask myself or ask a person who's curious about this is like, what's a reasonable workload for you over the given duration that you're going to compete at? So first, determine what race you are. Roughly how long is it going to take you to do that? What's a reasonable target for workload for you? And what I mean by that is, if you look at workload for the amount of energy demanded over the course of an hour. And that's where going to be a good starting point, because you have a scenario there where, like somebody who is in the front of the pack, they might be, you know, north of a thousand calories per hour at their workload for one hour, whereas you have someone in the back of the pack, they might be closer to like 500 calories per hour. So their fueling strategy is going to be different. The other way to think about it too, is like if someone is let's say we're taking a distance, most of these races are based on distance. So let's say we take a half marathon. You have somebody who is super elite in breaking 60 minutes in that versus someone who is out there going for a two hour goal. Those are two very different intensities being raced at because it's no longer your, your workload and where you fall on the intensity spectrum is going to be more based on duration than it is distance in that scenario. So you want to consider all these things. The other thing to consider too, is just like a lot of times when I see these topics discussed, you'll see a lot of the negatives being described as other issues that can arise, like, you know, ketogenic diet will cause this, that and the other thing. And, you know, to a large degree, I think like some of that, you got to look at what they're actually referencing for it to, because you have scenarios where it's like, well, yeah, if you miss apply a ketogenic diet or if you call something a ketogenic diet, and then it's actually something that is like maybe low carbohydrate, we're sort of comparing two different things and looking at the outcome and then attributing it to that. So don't take anyone's word with just like complete gospel and uh, you know, look into that stuff too and kind of figure it out for yourself to some degree versus just, uh, hearing something and then and then running with it. But that's kind of what I got for this particular one. Like I said, I'll link the study to the show notes, and then I'll also link Brady stuff there, too. I think that's a great starting point for anyone who's interested in diving a little bit deeper into this topic.