The Great Carb Con: Scientists Break Down a Shocking New Study
In this interview, host Nick Norwitz talks with metabolic researcher Dr. Andrew Kutnick about a comprehensive meta‑analysis and a series of randomized controlled trials that challenge the long‑standing belief that large amounts of carbohydrate loading are required for peak athletic performance. The discussion traces the historical origins of the carb‑loading myth to 1960s muscle‑glycogen studies, explains how those early findings were correlational rather than causal, and highlights the overlooked role of blood glucose – a tiny pool that fuels the brain – in limiting endurance. Kutnick’s work shows that a modest intake of about 10 g of carbohydrate per hour is sufficient to prevent the brain‑energy deficit and improve performance by roughly 22 %, a fraction of the 60–90 g/h recommended by current sports‑nutrition guidelines. The same performance is observed in both high‑carb and ketogenic athletes, indicating that muscle glycogen stores are not the primary driver of endurance. The conversation also addresses health concerns, noting that many elite athletes develop pre‑diabetes from excessive refined‑carb consumption, and argues for precision nutrition that targets brain fuel rather than massive carb loads. Finally, Kutnick outlines future research needs, including dose‑response studies and tracer‑based metabolic analyses, to refine carbohydrate recommendations for athletes.
Chapters
No athlete's health should ever be sacrificed at the altar of performance.
Not like 6 plates of pasta, too great.
There was something in those studies that was ignored, and that was—
You have this willpower and you're trying to like wring all the metabolic juices out of your muscles and just push yourself.
More reliable than any other biomarker that you can look at.
This really brings a new meaning to mind over matter.
And that's how we got to where we are. Sports Nutrition Guide.
4,000 calories from just carbs alone. You can have your cake and eat it too. I wanna frame up today's discussion with a myth I'm sure you've heard, which is you should eat carbs for peak performance. Now, as an ex-marathon runner, I always live by this mantra. I always obliged by it. Maybe it's a little bit of confirmation bias because I love Nutella and candy yams and marshmallows. But jokes aside, people accept this, I think, Not because it's been rigorously challenged, but because it's one of those inertia of status quo ideas. But a friend of mine, my guest today, Dr. Andrew Kutnick, recently blew up this myth with colleagues and in style. So he's here today to discuss a new meta-analysis of randomized controlled trials that is threatening this myth that you need to carb load for peak performance. So welcome, Andrew.
It's an honor to be here, Nick. Always appreciate to chat with you.
Well, I'm going to direct people to our past, I think now 4 interviews, if they want your bio. At a high level, just so people know a little bit about Andrew, he is a leading researcher in the metabolic health space, especially around blood sugar control and diabetes. And if I had to concisely summarize the characteristics that have him coming back again and again, it's the ferocity and integrity with which he approaches scientific research and scientific communication. I know that's gonna come through in this discussion, So let's just kick it off. Tell us about this new paper that you and colleagues wrote.
Well, it's, it's really cool to be here, Nick, 'cause I know you're an extremely curious person who has an incredible background in research and, and is continuing to kind of remodel and shape the field in many ways. So it's cool to be here talking to you about a paper in the context of nutrition, sports nutrition specifically. So we had done a number of randomized controlled trials over the last 5 years, specifically looking at the impact of very low carbohydrate diets in sports performance. Now, keep in mind that historically it was believed that carbs were deemed to be virtually essential for performance. You've seen many Gatorade bottles, gel packs, all these. If you've ever attended a sports event like a marathon or a cycling event, these are basically almost considered a part of the, the endurance sport religion. You know, it's like you need these and if you don't have these, you're gonna have poor performance. So much so that they have Gatorade bottles at various stops across many of these, these racing events. Now, the question was, you know, that by default means, Nick, that doing a very low carbohydrate diet would of course impair performance, right? And one of the key challenges to that is that there have been a number of studies attempting to look at that, but they're all short in duration. So we actually did a much longer study, allowed athletes, um, one of which was actually Ironman competitors, very high-end athletes to adapt to this diet for long enough. And what we essentially found is, uh, results that really challenged that belief structure. And so what we did is we said, okay, well, why are our results so different than what the sports nutrition guidelines seem to present? Uh, and so we actually looked at over 100 years of evidence, around 600 citations, and we actually analyzed over 160 different sports performance studies. And our specific goal was to understand if carbohydrates were improving performance in sports, how was it doing it, number one? And if it was doing it, we wanted to understand the underlying metabolism that was driving that because it would then keep us or help us inform how we administer these potentially optimally. And so, uh, what we found was actually a stark contrast to the current sports nutrition guidelines.
I do just wanna like relay the groundwork and ask the question, Where does this idea, what we call a myth, religion, whatever, the assumption that carbohydrates are required for peak performance, where does it originate from?
This goes back to the 1960s. So the, back in the 1800s, there's actually a number of reports that actually show that the Olympic athletes, the highest tier of athletes, were consuming a protein and fat focused diet. You can actually look at many of the cafeteria-based foods and many of the diet plans for athletes at this time. It was protein and fat focused, but But in the 1960s, a physician named Jonas Bergström developed the muscle biopsy technique called the Bergström muscle biopsy. And what they found when they did its muscle biopsy is that glucose molecules were stored in chains of glucose called glycogen. And of course, the assumption at this time was, well, if glucose is being stored in this tissue, it must be essential to performance. Well, lo and behold, Nick, they did find that the higher the levels of glycogen, the longer someone would perform exercise. It wasn't but 20 years later where they started developing these more novel techniques of assessing how much fat and carbohydrates your body burns using the amount of oxygen you consume and the amount of carbon dioxide you breathe out. And using a, a calculation and ratio, you can determine the amount of carbohydrates and fat that the body is utilizing during exercise. Well, yet again, they found that when you consume more carbohydrates, you were, of course, not by surprise, burning more carbohydrates. But those athletes who were burning more carbohydrates appeared to perform better. Now, this led to a belief structure again and again, ultimately to textbooks, what's taught still today in many, uh, exercise science classrooms, that carbohydrates are really important for performance. And so much so that even when you get to high intensity levels of performance, they're essential. For performance. The big problem with all of this, Nick, is that the association between glycogen and performance and the association between the amount of carbohydrates someone burns during exercise and performance were exactly that. They were associations. They were never causal, meaning glycogen levels were never causally linked to performance. Carbohydrate oxidation levels or the amount of sugar your body is burning was never causally linked to performance. Despite that, as athletes were consuming carbohydrates, oftentimes they would see a performance boost. And so this just precipitated the belief structure that carbohydrates are needed, and they're needed, Nick, for the total amount of sugar your body is burning and the total amount of glycogen in the body. Well, in a male or an average body weight male, you can store up to around 500, 300 to 500 grams of glucose as glycogen, and in females, somewhere around 300, give or take. And so that meant that you would need to replenish that, right, on a daily basis, especially for athletes performing high volumes of exercise. So this developed the belief structure around associations between these biomarkers and carbohydrates in sports. So if we need to replenish these high volumes of glycogen and burn high levels of glucose and sugar in the body, and they're associated with performance, well yeah, we should recommend athletes to consume upwards of 300 to 500. But now recommendations actually recommend some athletes at the very high end for an average body weight male to consume sometimes north of 1,000 grams of carbohydrates per day. And that's how we got to where we are on Sports Nutrition Guide.
But 4,000 calories from just carbs alone. A couple important things I wanna point out to lay the groundwork for where we're going physiology-wise. One is you said about 500 grams of carbs in an adult male body. That's in two buckets. So there's the liver, a small bucket, and then there's the muscle, which is a bigger bucket. But the muscle is specific, and I'm foreshadowing a little bit here because it doesn't actually defend blood sugar. The muscle is very greedy with respect to its carbs. It keeps it to itself. That'll become relevant later. The other thing I wanted to ask is, okay, what's the alternative model? So the logic's very straightforward. Carbs, quick burning fuel. So high intensity sort of exercise, you want quick burning fuel. You eat more carbs, glycogen stores go up, so you'd have a bigger tank for performance. That seems like a pretty logical chain. What are the leaps of logic that could lead to associations between, say, muscle glycogen and performance that are not causal?
Well, those actually directly, uh, Nick. So the, the non-causal link is this link between how much glucose you store in the muscle and how many sugar you burn in the body to your performance. These are all just associations. So as you see drops in the amount of glycogen in these muscle compartments, in various athletes, you would also see that athletes would fatigue on average earlier, or when athletes were burning less carbohydrates during performance, they would see that those athletes on average would fatigue earlier. But in those same pivotal studies, the 1960 studies by Bergstrom, and 1980 studies or '70s and '80s studies by Coyle, if I'm saying that correct, C-O-Y-L-E, a very prominent exercise physiologist. These were all association findings that pivotally changed the sports nutrition field. However, Nick Norwitz, there was something in those studies that was, uh, ignored, and that was actually the drop in blood sugar levels that was occurring in those same studies when fatigue would occur. So not only was glycogen coming down in the 1960s studies,, but so was blood glucose levels. Not, not only was carbohydrate oxidation levels predicting performance, but when athletes hit fatigue, their blood sugar levels would drop. Now, it's very important to establish that we have known for years that low blood glucose levels in the blood leads to a brain energy deficit. A brain energy deficit is one of the most reliable mechanistically linked ways to cause a fight or flight response and an impairment in performance. This has been known since the 1920s, Nick. And in those same pivotal studies where they have focused on muscle glycogen and focused on the amount of sugar that your body's burning in total, we're also seeing this clear drop in blood sugar levels, which we have known for over a century is causally linked to the drop in performance. You drop blood glucose levels, you will impair someone's performance, not just physical, Nick, but also cognitive performance, because the brain is one of the most pivotal tissues in the body. And when you deprive it of energy, of course your body will go into survival mechanism. That means that it will take energy away from functional movement to prioritize sustaining enough energy for the brain. And of course that means impairing performance.
I wanna really highlight something that is very easy to miss, which is we've established now on these early studies and muscle glycogen, there's a decrease in performance, but there are really two pools of carbs we care about right now. There's the muscle pool, which does not feed into the blood, and there's the blood pool, which can feed to the brain. So now we have an alternative model where it's, okay, maybe it's something going on in the central nervous system, not the muscle that is limiting performance. And then Can you tell us, okay, we said about 500 grams of carbs stored is as muscle glycogen, the liver and the muscle, which is mostly the muscle, 500 grams. How much is in the blood total?
For an average body weight, uh, male around 5 grams, the whole bloodstream.
So it's a hundredfold less than the glycogen stores. And that's something like 1/3 of a tablespoon of honey. Like a tiny bit of orange juice, and then that's all the, I get that is your entire blood sugar supply. When you're saying during exercise that blood sugar was dropping, I know it wasn't dropping from 90 milligrams per deciliter to zero. How much was the draw that was associated with decreases in performance?
So what was most consistently shown, so when we looked at over 600 citations, 160 different sports performance studies using carbohydrates as a nutritional tool to test whether improved performance. The most pivotal finding, Nick, that we discovered was that 88% of the studies that showed an improvement in performance with utilizing carbohydrates as a treatment for sports performance, it wasn't what was happening in the treatment group, Nick, that predicted performance. It was actually when you looked at the placebo group or the group that wasn't receiving carbohydrates. And in the group that did not receive carbohydrates, they would see an 88% of studies more reliable than any other biomarker that you can look at related to performance was a persistent reduction in glucose levels, meaning that an athlete could start around 90 to 100 milligrams per deciliter on average. And then what would happen is they would slowly drop. Into or near hypoglycemic range. And it was actually more so the level of around, let's say, 20 to 30, sometimes 40 milligrams per deciliter drop.
The amount of the drop, they're not dropping to 20 or 30, they're dropping to like 60.
Correct. So they're going from 90 to 60 or 100 to 70, uh, around those type of numbers. And that subtle change was able to induce dramatic shifts in the functional capacity of the body.
I'm trying to develop a visual for this. Maybe you can help me. But when we're saying that these different pools, we have this assumption you want to carb load your muscle glycogen stores, let's say 400, 500 grams of carbs. That is plates and plates and plates of pasta. But you're saying the change in the blood sugar is the equivalent of, you know, about maybe a fifth to a quarter of blood sugar levels, which is 5 grams on average. So let's say like 1 to 2 grams, that is the equivalent, the sugar equivalent, and I'm not kidding here, I think you can check my math of like maybe 2 grapes, not like 6 plates of pasta, 2 grapes. It is that change, that magnitude in sugar in your blood that could be changing exercise performance. In theory, if you could snap your fingers and turn all the sugar in grapes into bloodstream sugar, which you can't, but That is effectively what you're saying.
Exactly, Nick. Actually, more like one grape because there is no metabolite in the body that is more protected than blood glucose levels. The body does so much to keep blood sugar levels between 70 and 120 milligrams per deciliter on average throughout the day, no matter whether you're eating, whether you're sleeping and not feeding, or whether you're fasting for extended periods of time, the body has developed so many regulatory mechanisms to make sure that glucose stays stable even when you consume zero glucose within the diet. So that's really important to appreciate because that illustrates how important it is. And some of the key examples of this is when blood sugar drops, Nick, 'cause on a prior episode we talked about the elevation in glucose and the impact that it can have on the body. But what we're talking about here is a subtle drop in blood glucose that causes a clear signal within the brain of, brain energy deficit and a well-established, very consistent counter-regulatory neuroendocrine response where you have elevations in adrenaline or what we know as catecholamines, epinephrine, norepinephrine, elevations in cortisol, elevations in this critical hormone called glucagon, which work to liberate key tissues within the body to restore blood glucose levels.. But those same molecules, but also the brain energy deficit, is clearly linked to impairments in functional capacity of tissues like the muscle and has been causally associated with decreases in performance.
So you mentioned that in your meta-analysis, you noticed in those studies where carbs did improve performance, the control group that wasn't receiving carbs had a decrease in blood sugar. So I'm assuming where there wasn't a decrease in blood sugar in the control, there probably was very little performance improvement with carbs. Is that first the correct assumption? Correct finding?
That's correct.
And second, you're not talking about this brain energy deficit, that little decrease in blood sugar, not muscle glycogen, but blood sugar being causally linked to a decrease in performance. How can you claim causality there?
So that's a, that's a great question. So let's back up for a second and actually look at some of the studies that allow us to actually look at whether glycogen levels, uh, are actually causally linked. So there have actually been mechanistic animal studies where they're, they genetically modify key enzymes in the body that actually cause the muscle to be hyper-saturated with glycogen. So an abundance of glycogen. And they found that in these animals, a mouse model, um, or what we call preclinical models, they found that that hyper-saturated muscle glycogen did not improve performance.
Be clear though, is this, but like in glycogen storage diseases, various, you can have a saturation, but it's not allowed to liberate the muscle glycogen. And these models, could the mice actually break down this glycogen and use it?
Yes, they could because they, they would actually, they, they were able to build up abundance of muscle glycogen, but they could also utilize it, but that had no impact on performance. So that is one of the clearest signs. If you could actually causally elevate glycogen levels, you using alterations in the genetic enzymatic capacity of animals and have a matched animal with all the same genetic background, but just less muscle glycogen, and there's no difference in performance. This is one of the clearest signs that muscle glycogen is not causally linked to performance. But they've done the same thing with liver glycogen. And guess what, Nick? It does extend performance.
Wow.
Okay. So illustrating that the, these This small glucose pool that is the, the what's in the blood, but also restored by the amount of glycogen in the liver, cuz liver's predominant place in which you restore blood glucose levels. That does impact performance when you causally look at it. But we look over here on the other end where you actually can assess this cuz you can't really do these type of genetic knockouts in humans, of course. Um, when you actually hypersaturated it in animals, you don't see this improvement in performance. And that's actually some of the most compelling evidence. That supports all these years of evidence going back to 1924, '25, and '26, where actually, school year from Nick, Harvard medical physicians actually assessed the blood glucose levels in athletes who were running the Boston Marathon. Nick, you ran the Boston Marathon, didn't you?
That's a long story. I, I did the Boston Marathon. Yes. It was not a run. There you go. It was, I had a broken tibia, so I crutched it.
But it's still very, very impressive. Maybe a PR with a fractured tibia though. So that's, that's pretty impressive. But let's, let's say that all the way back in 1921, there were Harvard physicians who actually looked at Boston Marathon finishers and were finding that many of these athletes either could not complete the race or were coming to the end of the race with slurred vision, pale skin, were losing the ability to speak clearly and, and actually function normally. And when they tested the blood of these athletes, it's called The Constituents of Blood in the Boston Marathon in JAMA in 1924, they found that the only change that was meaningfully altered was blood glucose levels. So the next year they provided these same athletes with, what did you expect, carbohydrates of various sources. And every single one of these athletes had better performance. Okay. So this was the first initial study actually looking at this effect. But we know from array of different datasets, Nick, where you, one, you see this, this drop in blood glucose levels and impairs performance, but you also see that in various studies in type 1 diabetes, the disease that I actually currently live with and have since I was 16 years old. So almost going on 2 decades, you can manually alter blood glucose levels. And once you get into hypoglycemia, it's one of the most reliable ways to directly cause impaired performance, not just physical performance, Nick, but also cognitive performance. And the magnitude of deficit in performance is typically around 5 to 20%. So, it's very meaningful how much of a drop we see. But what's also interesting, Nick, is some of the randomized controlled trials we have done that we have worked to just provide only a minimal amount of glucose to restore, uh, or minimal amount of carbohydrates to restore blood glucose levels, we were able to see similar improvements in performance as we see decreases with brain energy deficit.
So just to review for people, what we've established so far is that when it comes to performance, what matters is not your muscle glycogen, but if there's a blood sugar drop in the blood, which is a very small change, we're talking about the order of like 1 to 2 grapes worth of sugar. You're hearing maybe two stories because what we could be perceived as saying is that carbs don't improve performance, period. But a more nuanced view would be they can, but how they do so differs than what one might expect. And the implication of that is also very practical in terms of how you use carbs and how much you actually need to improve performance. So a very simplistic way of thinking about it is like, you know, a small nectarine or half an apple could provide the same performance boost as a giant bowl of pasta the night before. With that, I want to get into some of the practical. So I'll open up with the question: in the randomized controlled trials you've done where you've provided small amounts of carbs to stabilize blood sugar so it doesn't drop to improve performance, what is the magnitude of carb needed to get to peak performance? And how does that compare to what is recommended and what most athletes do?
So when we studied Ironman competitors and we specifically only provided enough carbohydrates to maintain blood glucose levels, but not enough carbohydrates to one, spike insulin, two, dramatically shift glycogen levels, and three, dramatically shift the amount of carbohydrates the body burns. That was important because if we shift any of those 3 variables dramatically or significantly, then of course it may lend someone to hypothesize that one of those other factors was the key contributor. But what we've found, Nick, is that around 10 grams per hour was sufficient to not only improve performance of high-carb athletes, but also very low carbohydrate ketogenic athletes on average across both diets. 22%. Now, in contrast, sports nutrition guidelines, American College of Sports Nutrition, Dietetics Association, both United States and Canada, ISSN, Gatorade Sports Science Institute, they all recommend 5 to 12 grams of carbohydrates per pound or per kilogram. And also during exercise, they recommend upwards of up to 60 to 90 grams of carbohydrates per hour., which is a tremendous volume of carbohydrates, but on the order of 10 times more than what you were giving.
You were saying up to 90 grams per hour versus 10 grams per hour.
So yeah, so 6 to, 6 to 9 times lower is the amount we gave while still maintaining a 22% improvement, which is very consistent with the improvements we see in similar types of studies when giving even way higher volumes of carbohydrates.
What exercise tests were you doing? So these were triathletes, Ironman triathletes. So these are like top-class athletes, probably working at a very high intensity. What was the exercise test you were doing?
So we took Ironman competitors and got them to do, uh, a cycle test. So we got them to do 70% of their maximal aerobic capacity, and they were to sustain that for over 2 hours in duration. Now, the reason this is important is because we wanted to make sure that the competitors were, or the athletes engaging in these bouts were sufficiently trained to allow them to go for prolonged periods and be a good representation of what's happening on this higher end. And So when we asked them to go, we asked them to go until they, quote, hit the wall. And what hitting the wall means is they were no longer able to maintain a 70% output throughout that performance bout. Now, someone may ask, well, then does it only apply to cycling? And why did you choose cycling? Well, we chose that mainly because it is one of the cleanest ways to get at this question. You know, if you're running or you're doing resistance exercise, you don't typically lift weights nonstop for an hour straight. You lift weights, you take a break, and then you pick 'em back up again, put 'em down, take a break, repeat, right? But in cycling, you're sitting down on a bike and consistently putting out a, a, a consistent amount of power and also consistent amount of VO2 max or percentage of your VO2 max. It's very controlled. It allows us to get and remove other confounding variables from the study so we can cleanly ask the question, does this amount of carbohydrates significantly impact performance? But in one, yes, we saw that it did. But it's also important to appreciate the historical literature here, Nick. When you look at historical meta-analyses in other forms of sports, even resistance exercise or anaerobic sports, we see that carbohydrates do not consistently improve performance, Nick, until the Exercise is, one, sufficiently strenuous, and two, for sufficiently long. So typically over 45 to 60 minutes in duration. Well, guess what, Nick? You don't get drops in blood glucose until after that point, which is very consistent with our findings regardless of sport. So we just chose the model to be aerobic exercise and chose high-end athletes in that because it allows us to get at the question in a very controlled manner in a laboratory setting. But these findings are extremely consistent when looking at other studies when carbohydrates do and do not improve performance in various diets. And that's typically anything over 60 minutes in duration, regardless if it's aerobic, like cycling, running, or anaerobic, like resistance exercise.
A lot there to unpack. I think, again, making it very clear and practical. So if you're working out for less than an hour, Carbs are gonna help more than that. Even in these tests with these very high-level athletes, Ironman triathletes, when you're putting 'em on a bike and having 'em exercise for hours, and if people want a sense of how hard they're probably working out, I'm guessing they're 70% VO2 max. They're putting out well over 300 watts consistently. If somebody wants to go to the gym, sometimes they have a watt output on the cycle bike. Try to hold, I don't know, 350. I don't know what their average was. Let's say 300 being liberal. See how long you can hold that. See, at the level of intensity they were probably going, again, probably much more than that for hours. And you're saying they needed the equivalent of possibly a third of a banana per hour to hit peak performance. That tiny bit.
In fact, and also in that study, Nick, to your question before about how do you know what's causing changes in performance? Well, we also, we're seeing that number one, we used two different styles of diet. We did a diet that we know typically lowers muscle glycogen levels in the form of ketogenic diet. Okay? So we were able to do two different diets with distinct levels, at least based on the model of muscle glycogen. On top of that, we also know that ketogenic diet athletes typically burn much higher levels of fat and much lower levels of carbohydrate. So again, showing a distinct level of the amount of carbohydrates that are being oxidized. And what we found is that the ketogenic diet athletes performed exactly the same as the high carbohydrate athletes. Okay. So let me say that first, because that then disavows the association between the amount of sugar you burn and the amount of glycogen levels being associated with performance. Obviously they were distinctly different across diets, but yet they had the same performance, but both groups got hypoglycemia.
Nick Norwitz, were they the same hypoglycemia threshold? Or did they have different baselines?
So that is a very good question, Nick. Something we didn't actually, uh, publish this on, but the very low carbohydrate athletes had the same level of performance but had higher incidences of hypoglycemia. So why is that critical? If you actually calculate not just glucose, Nick, but also ketones and lactate, two other circulating metabolites that also fuel the brain. And you equate that to what was happening in the high carbohydrate diet. They had equivalent total circulating brain energy metabolites in the blood at the time of fatigue, the lower glucose, right?
In the low carb adapted athletes.
Correct. Because they had higher ketones and higher lactate. So again, what this is showing is that they had the same degree of performance, the same, uh, uh, feelings of fatigue, um, throughout the entire exercise bout. But yet one had lower glucose, but yet higher ketones and lactate, and the other had much higher, uh, uh, subtly higher levels of glucose, lower ketones, and lower lactate. But to, in total, Nick, the amount of brain energy fuel floating around the blood was equal and they had equal performance. That's also a key point because it again illustrates that it isn't so much the degree of hypoglycemia, which was higher in the very low carbohydrate group, it was the degree of circulating brain fuel that was in the blood. This is what we found in our review, looking at over 100 years of data, 600 citations, again, north of 160 exercise performance studies. When we were looking at various biomarkers, the one biomarker that constantly consistently popped out was the biomarker we know is linked to brain energy metabolism. Blood glucose levels. And we've also done randomized controlled trials and seen that despite having lower glucose levels but having higher levels of other brain energy fuel like ketones and lactate, that helps provide sufficient energy to the brain and allows for equivalent exercise performance across either diet. So what this also showed, Nick, was it just that blood glucose levels was so important, but more importantly, that the brain energy metabolism was guiding performance outcomes in these athletes. And that's a paradigm shift because again, it changes away from just focusing on the amount of nutrients in a muscle compartment towards the brain compartment, which we know if you don't have the brain functioning or, eh, then you're not gonna perform well. And it's quite obvious to most people, but One of the most consistent benefits, uh, in ex sports performance is the placebo effect, the perception from the brain that you're gonna perform better. We've known for years the brain's critical to performance, but it often is underappreciated when you go to a marathon race or a cycle race or a triathlete race or any of these other, or go to a gym in general and all you see in the, the shelves is just abundance of sugar water everywhere because that has been in focus. For years and years and years. And so what this review illustrates is the ability to rethink about how we view performance away from just loading up tremendous amounts of carbohydrates towards focusing on precise and precision nutrition towards precise amounts of carbohydrates only when appropriate.
This really brings a new meaning to mind over matter. Or mind over muscle. I think people say that in the sports world and they get this idea of you have this willpower and you're trying to like wring all the metabolic juices out of your muscles and just push yourself. But what you're really saying and what we've kind of built to is this idea that no, no, no, it's not even muscles that are limiting. It is literally brain metabolism that is dictating the threshold to which you can physically put your, push yourself. Not a matter of willpower, just like, The checks and balances in your body, they're dictated by your central nervous system. And then the blood energy, primarily blood sugar, but also ketones and lactate, that is dictating performance. And that has tremendous impacts on what you just said, which is precision nutrition. How do we optimize performance? And it's not the bowl of pasta before the marathon. It is as little as a third of a banana during high-intensity exercise that lasts over an hour.
And to that point, our body has shown us this for years. When you consume carbohydrates, the first place that insulin goes to store those carbohydrates is in the muscle. The insulin is released in the hepatic, also known as the liver portal vein, to immediately shuttle insulin to the liver first, because it wants to resynthesize the critical storage compartment for glucose for the brain. Only after that, then does that insulin go out to the circulation where then it goes to not necessarily muscle first, or it, it actually goes to the fat and binds at very high potency to shut down the level of fat that's being broken down. Only after that, when there was sufficient abundance sufficient abundance of food signaled by high insulin levels, does the muscle then get the excess glucose levels to then store it? This is the perfect illustration of our body telling us where the priority is in survival, which is why when you have a drop in blood glucose levels and low— as an illustration, low liver glycogen to be able to resynthesize that blood sugar level— you consistently see impairment in performance. However, we don't consistently see impairments in performance when muscle glycogens are, are low. It's only often associated because of course when you consume more carbs, you tend to have more muscle glycogen. Okay. So it's been a missed signal for years where the sports nutrition guidelines have been taking it to recommend absorbent amount of carbohydrates. And in some cases we've seen in some of our randomized controlled trials that some athletes on high carbohydrate based diets consistent with sports nutrition guidelines are developing things like prediabetes, which we know is driven not just by the food, it's driven primarily by the food environment. And this is one of the most important things from this analysis is that yes, we know that you can consume 6 to 9 times less carbohydrates. And it appears that that is consistent with the biomarkers that actually predict performance primarily. But also beyond that, Nick, there's a health component. You know, no athlete's health should ever be sacrificed at the altar of performance, but yet they are and they don't know it. And it's important that this research article gets out there and is shared because it should allow us to reevaluate this push for these absorbently high levels of carbohydrates, which even prominent athletes like individuals like Lionel Sanders who is an Ironman champion, who's lean, high fit, high levels of fitness, exercising sometimes over 4 hours a day, also developed prediabetes recently and ultimately illustrated that these highly high levels of refined forms of carbohydrates that he was consuming was the predominant reason he was developing it. Because when he reduced 'em, guess what went away? His prediabetes.
What you're saying is that, and I think a lot of people know this, but it's worth putting out there and being direct about it. Being a high-performance athlete, looking elite does not actually parallel health. You can be falling apart on the inside. You can be eating a diet that fuels max performance, or let's say is compatible with max performance, and it can still be damaging your health. But the implications of the research that you are doing, that you are putting out there, is saying, pardon the turn of phrase, you can have your cake and eat it too, performance-wise. In this case, you're not actually having a cake, You're having a third of a banana so you can reach max performance as an athlete and still eat a diet that isn't slowly poisoning you. Do you think most athletes understand that?
No, they don't. Because if you look at, uh, any major athletic event, there is a consistent belief that that is needed to perform. Even so much so where I had, after we published our article seeing that 30% of athletes were getting prediabetes, I had clinicians and pretty high-level athletes, Nick, uh, of course not disclosing any of these people, um, were reaching out and saying, hey, I have that issue too. I have elevating, uh, my glucose levels have been persistently elevated over time and I never knew what was causing it. And it, this is critical because, and I said, well, have you ever considered doing some of the nutritional strategies that reverse it? And they said, well, no. 'cause that's gonna impair my performance. So it's one of the most common reasons that an athlete will choose not to do a diet that we know has plenty of evidence. In fact, the most evidence-based diet we know to drop blood glucose levels from prediabetes and diabetes range into normal range is very low carbohydrate ketogenic diets. That is the most evidence-based diet for improving glucose control and also reducing insulin levels. But yet many athletes will forego that approach because they're concerned about their performance and also being told inappropriately that these diets will not meaningfully impact their overall metabolic health. But in reality, we are seeing that a percentage of athletes are observing metabolic health issues. At least their biomarkers are clearly illustrating that. And athletes should know that they can perform on diets that are not only consistent with their performance, but also consistent with their health.
Hope people realize how profound that is. And this is also a good place to end or near end. I do have one or two more questions. Science is always a process of asking new questions and doing the next experiment. So what is the most important next experiment that needs to be done to move this field forward?
I think the most important thing is to do a dose-response study looking at graded levels of carbohydrates because we looked at 10 grams, but We didn't directly compare to 60, uh, 90, 120 grams, which some athletes are pushing levels that high or not higher. Uh, there's been reports of over 200 grams per hour. So a dose-response study, but also if possible, tracer-based analysis, analysis that allow us to truly refine, look at what is happening in the metabolism of these athletes at these graded levels of carbohydrate intake. Does it impact performance? And if so, is there a dose response? The evidence would suggest probably not, at least when you look at 100 years of evidence. But what then happens to your metabolism if there is an or is not a performance impact? That'll be an incredibly important study to look at.
One more question I had that I should have asked earlier, which was, you know, for those people listening who are, uh, um, fat adapted or keto adapted athletes, a lot of these studies have been done in mixed macro athletes. So people eating carbohydrates at baseline. How, and I'm gonna allow you to speculate here, not that you need my permission, but because I know evidence is limited, would these findings change in someone who said had been strict low-carb keto, let's say even carnivore, let's say zero carbs at the extreme end for, I don't know, a year.
So we don't actually know that answer, Nick, because all the studies we've looked at is 4 weeks or more in duration of a ketogenic diet and we see no impairment in performance. If they were able to adapt to a year, we certainly would expect that there would be even greater levels of adaptation. 'Cause even things like muscle glycogen levels don't really normalize. It, it doesn't appear for up to 12 weeks in athletes when they go into a ketogenic diet. Not that that seems to impact performance, but there are a number of physiologic changes that are not complete on a ketogenic diet just up to 4 weeks. Although what we see is that 4 weeks is required to have performance, no impairment in performance on the ketogenic diet. So it's a really interesting question, Nick, that we don't have the answer to. I would suspect that there's a possibility for greater levels of adaptation adaptation towards fat metabolism and ketone availability, which could meaningfully impact these outcomes across studies. But of course, that's a very hard study to do.
Yeah. Especially if we're talking, everybody always wants to ask like, oh, show me the RCT. But there are certain RCTs that are just next to impossible. This will be one where imagine the athletes, they're gonna say, yep, I'm gonna sign up to be randomized to a diet that might not fit my preferences even though athletics are important to me and I'm gonna do it for a year. So even beyond just the funding, you know, some of these trials are next to impossible to do. But anyway, questions to ask, always a frontier. Well, thank you for your time. I'm gonna let you get off to your next intense sports competition of childcare. But before you do, where can people find you and learn more?
People can find me at andrewkutnick.com where I put a lot of free resources out there. If they wanna find a way to contact me, there is a, a way to contact me through that website. But I'm also on Instagram and YouTube Andrew Kudnik, PhD, as well as LinkedIn and TikTok. You just search my name and you'll be able to find me.
Thanks so much, man.
Honor, Nick. Appreciate it, sir.
