Paul Laursen (00:00)

the muscle glycogen, is there more of a sink, a glucose sink that will always absorb up safely

glucose to prevent the glycation issue that's going to advance our aging and therefore it protects the individual

Paul Warloski (00:41)

Hello and welcome to the Athletes Compass podcast where we navigate training, fitness and health for everyday athletes. There's some new research in the pipeline that's going to change or might change how we think about why carbs help endurance athletes at all. The mechanism everyone assumes glycogen may not be the main story. However, we had this phenomenon going on in endurance sports, Sabastian Sawe

just ran a 159.30 in London for the fastest world record marathon ever breaking two hours. And his coaches publicly said he ingested 100 to 120 grams of carbohydrate per hour. Meanwhile, your average age group runner is or cyclist, triathlete is reading the same headlines, reaching for the same gels and wondering what is going on here? Are they leaving fitness on the table? So first of all, Paul,

what's actually happening at the front of these world-class marathon or triathlon events right now? We hear these numbers that are 90, 100 or more, know, grams per hour. What is, what's going on with that?

Paul Laursen (01:54)

Yeah, you know, we've we've been this has been growing this this movement has been growing Across the last few years, I guess Paul and the the doses of carbohydrate that are being Reportedly taken are getting higher and higher and higher And this is across the world tour cycling teams ⁓ Across our triathletes at the top level and now here with ⁓ with the with the ⁓

the two hour barrier for the marathon just being shattered, ⁓ not just by one individual, but two individuals with three going under the world record prior to that. I mean, just phenomenal. And the question really is, is it the high dosing carbohydrate levels that are enabling this?

Paul Warloski (02:39)

Mm-hmm.

Paul Laursen (02:49)

Is ⁓ it causation or is it just a correlation, right? And that's, I don't think we'll ever really know the exact truth. ⁓ But we really need to look into probably what the research and the data ⁓ suggests. And we have to think about, is this practice appropriate for me as well in whatever endurance event?

Paul Warloski (02:57)

Hmm.

Paul Laursen (03:19)

that I'm doing. maybe, yeah, I think that frames the question that will dance around first and foremost. But maybe we'll start with a little bit of science and that is, at the end of the day, what is quite clear is that these high doses, when we add more higher dosages of

Paul Warloski (03:24)

Mm-hmm.

Paul Laursen (03:44)

carbohydrate in the research setting in well-trained individuals, we don't see that there is an increase of performance ultimately with respect to more or higher carbohydrate dosages. To a certain threshold, maybe above 10 or 20 grams per hour,

that matters, but not really above that. And you might kind of say, well, why is that? Surely, you know, you're giving more fuel, right? Then surely that there would be more, you know, heightened ⁓ performance response. But this is, and we've spoke about this a little bit before, there's kind of, there's an old school way of thinking, and there's this new school of thinking on what carbohydrates are actually doing.

Paul Warloski (04:20)

Yeah, what's going on?

Paul Laursen (04:41)

And the main thing, to make a long story short, the main thing that carbohydrates are doing, according to the latest review by Tim Noakes and colleagues in Endocrine Reviews, one of the highest impact journals that we have out there, they frame this new theory around a large glucose pool in your body, that's the muscle glycogen.

and a small glucose pool, which is ultimately the glucose that floats around in our brain, and that which is ⁓ also produced by the liver. So that's the small one, and we've got the small one and the large one. What we used to think was that the large one was the one we needed to protect. We need to protect that muscle glycogen level, and if we supplement carbohydrates at high dosages, then we'll do that. The data doesn't support that. That's what the Noakes endocrine review

journal article suggests at the end of the day is that it's really all about preventing hypoglycemia, preventing a fall or a crash in your blood sugar, preventing that feeling of weakness that you might have or experience in your day when you get hangry, say for example, this is really all you need to do at the end of the day to maintain performance.

The body can go about getting other substrates and fuels. It doesn't have to go with muscle glycogen. It can burn more fat. But the one thing that you must protect is your blood's level of glycemia. It needs to be at a homeostatic level that your body says, okay, good, I've got energy, enough energy there that I can push forward. So that's what the science supports,

doesn't support that that large glucose pool is protected or that you burn more ultimately, or sorry, you will actually burn more carbohydrate. ⁓ But if you just had a small amount, you would just burn more fat instead. So there's no added ergogenic effect past preventing the hypoglycemia. So. ⁓

Paul Warloski (06:51)

Can you go

back and explain what you meant by burning more?

Paul Laursen (06:55)

Sure. So when we burn more, we're talking specifically carbohydrates or glycogen. So when you ingest a higher dose, so let's say we had a baseline level, we can all agree that at least 20 grams an hour is necessary to maintain performance. And the Philip Prinz study from 2025 supports that, where just a reminder,

in the Philip Prinz study, and this was AJP's award-winning paper for the year. What the authors showed in that study was that in both, had athletes adapted to a high-fat diet for six weeks and a high-carbohydrate diet for six weeks. Either diet, the same subjects, so I believe it was 12 well-trained triathletes, they both did both diets.

and they were both chronically adapted to both, either high carb or low carb, but at the end of the day, all that was needed in either condition was just 10 grams an hour of carbohydrate to elicit an improvement of performance. If they didn't have that carbohydrate, their performance suffered and they lowered their time to exhaustion, I believe at 70 % of the O2 max. Okay, so.

First and foremost, we can all agree that a small amount of carbohydrate improves performance in both low carb and high carb athletes. Case closed, no question. We're not saying don't take carbohydrates. It's the quantity that we're discussing here. Do I need to cake up the 200 or could I get by on a little bit less? So let's say now we've all agreeing on the low amount at least is needed. Now let's try adding more to that amount.

So when we do that, what we find is that the body starts burning more glycogen with more carbohydrate that you're taking on. And that's a bit of an odd one, right? Like why, ⁓ you know, we often thought that by taking on more carbohydrate, you know, the saying that we have in exercise science and exercise physiology is that we should be sparing muscle glycogen.

And so Dan Plew's Rothschild, there's a review where they did a meta-analysis of all of these. And they basically, there was a subtle, but almost a wash in terms of whether carbohydrate taken during was sparing or burning more carbohydrate. It's about even. it doesn't support the fact

The data does not support the fact that it spares muscle glycogen. In many cases, it can exacerbate or burn more carbohydrate by taking on higher doses of carbohydrate, especially through to 90 grams an hour, for example. And that's an odd one, right? So why are we burning more carbohydrate if we're taking on more carbohydrate when...

Paul Warloski (09:56)

Mm-hmm.

Paul Laursen (10:03)

we're like burning more glycogen, just to be clear, not the carbohydrate you're taking on, we're burning more glycogen at that point. And because that was the whole premise that we used to think about, we used to think we actually want to spare our muscle glycogen, and that's not necessarily what the data is supporting. So this all goes back to the model that we spoke about with the small pool and the large pool, that first and foremost, at least for...

all of us across the spectrum of endurance, from the age group that's just starting to the elite that is out there, we must protect that small glucose pool, must have at least a small amount. Where it's debatable is what it's doing within the large glucose pool or the muscle glycogen level. And it doesn't look like it's doing much there, according to latest science.

in contrast to what we thought it did.

Paul Warloski (11:00)

So I'm confused then. You've got some science coming in that says that this carb performance is a little complicated, but there've gotta be peer-reviewed studies that show carb feeding improves performance, aren't there? And then how do we square that?

Paul Laursen (11:20)

Yeah, carbohydrate, again, that's not debatable. So carbohydrate compared to placebo improves performance. No question. So no question that it does. But it does so not through a sparing of muscle glycogen, the large pool. It does so through a sparing of the glycemia, the small glucose pool. And the general gist is that you just don't need these high doses to do that.

Paul Warloski (11:28)

Okay.

Paul Laursen (11:49)

you can do it on much less. And then if you really wanna, if you wanna look at what's important to the everyday athlete, they're probably doing their, performance might be very important for them, which is why they might be tuning in and listening to this, but health could also be important for them as well. And if health is important, we need to be careful about spiking our blood glucose level because it,

we have too much glucose, we have too much insulin level, and too much insulin means that we're going to be blocking our ability to burn fat. And we wind up being, you we can become metabolically inflexible. And usually that's what you're trying to do. When you're an endurance athlete, you're one of the hallmarks of being a good endurance athlete is to have a really solid foundation, aerobic foundation.

of an ability to burn fat in your mitochondria to produce ⁓ exercise performance, right? So produce power. So if you're always potentially sabotaging that with higher dosages, with high spikes in blood glucose, you're gonna be also experiencing high spikes in insulin. So it's a balancing act, I guess, Paul. ⁓ But yeah, I think we just need to be really cautious with the messages.

Paul Warloski (13:11)

Hmm.

Paul Laursen (13:16)

that ⁓ are kind of getting out there. And the other really important point is that we can't not acknowledge the practices that are being purported to improve this performance in the elites. Something, we might be missing something and we're open to saying there's some other potential mechanisms that could be at play that no one across any of the science

Paul Warloski (13:32)

Right.

Paul Laursen (13:46)

factions has underpinned yet and we're all waiting to see what those might be.

Paul Warloski (13:54)

You know, at least the elite athletes that, know, who are maybe not placebo prone describe often a switch flipping or another gear opening up when they take the sugar mid-race. What do you think's going on with that?

Paul Laursen (14:11)

Yeah, that's, I think you nailed it, Paul. And that is, that's what I'm hearing as well too, from elite coaches. This was, this was through a friend of a friend with a, coached a 205 marathoner with a, which is an incredible, incredible time, but also using this high dose method. thing that's really important, ⁓

Paul Warloski (14:29)

Mm-hmm.

Paul Laursen (14:37)

to note in that for this 205 Marathoner is the frequency of the dosages that were being used. So somehow within the setting at the elite level, and this will also be of course in the Tour de France, and the Pro Tours, and of course even in Triathlon as well, but that frequency of dosing can be as you want it to be. ⁓

Zuckendrup did a series of classic studies before showing that mouth rinsing without even ingesting the carbohydrate elicited improved performances. Okay, so just, you know, make sure that that's clear in your mind. The series of Zuckendrup studies showed that even without ⁓ any of that substrate coming into the body, there's a heightened improved performance, right? So your central governor, if you want to follow the Tim Noakes kind of...

Stan is somehow able to go to a new gear with the mouth rinse ⁓ aspect, or the mouth rinse technique that signals to the body, to the brain, energy is there, and we can elicit a new gear as a result of that. I think, Paul, that that is, that's something to that effect is being unleashed.

with those high frequent and high concentrated carbohydrate dosages in these contexts because we're hearing about the frequent aid stations that the elites are allowed to utilize in these world marathon majors and of course in the tour peloton, in the elite triathletes, et cetera, et cetera.

Paul Warloski (16:25)

Mm-hmm.

Paul Laursen (16:26)

continue, think one of the ergogenic means is the frequency of the stimulation during how, in that higher carbohydrate dose. Could that be useful for an endurance, an amateur? Possibly. But we also need to acknowledge the

potential confounder too with GI disturbances are often reported in endurance events, endurance athletes with higher concentrations of carbohydrates. So it's definitely not something you would want to do as a one-off. You would want to rehearse this in some of your training sessions that are specific to the race preparation.

Paul Warloski (17:11)

So are you saying that the carbs are almost acting like a drug on the brain?

Paul Laursen (17:19)

Perfect, yeah, you nailed it, Paul. That's exactly it. So this is really where we're going with this. We don't know for sure, but that's almost what, that's the only thing that's left we can think that is happening because at least within the context of the well-trained, so these are athletes with VO2 maxes of around 65, 60 to 65 in many of the studies.

the Phil Prynne's studies, et cetera, that are doing, we're not seeing any changes in performance that metabolism can describe. we're not seeing that, and when we say metabolism, we're talking about like fuel on a car. We're thinking about a lot of this, you know, when you think about how this mechanism works, you think about, I'm putting more gasoline into the car.

And I'm using, I think Peter Attia described this once, but this is actually, we know this is incorrect now. He described it as adding a higher octane fuel ultimately to the system. And that higher octane fuel is burning hotter and therefore there's more output as a result. We can't find the data that supports that. If that data exists within the ⁓ walls maybe of the

Paul Warloski (18:35)

Hmm.

Paul Laursen (18:42)

the carbohydrate manufacturers that are producing these, we're just not privy to it, but we can't find it from any of the work that we're doing. There's no study that shows that. But we totally know that that's not what practice is happening. So that leads us, right to exactly what you proposed there, is that this seems to be some sort of a pharmacological or drug ⁓ mechanism.

that's maybe related to the mouth rinse, Juke and Drup studies. But that, and again, let's reflect again on that 205 marathoner, that 205 marathoner, when asked what happened, what did you feel, his reply, something was unlocked, right? So something is being unlocked that is across that elite performer's body, and they're able to,

drive it from gear five into gear six or whatever it may be, right? Whether doing something super special on that day. And maybe there's also the fact that something needs to be on the line, right? So the motivation factor potentially as well and potentially some interrelated factors that are all going into this. But it's not as simple as just that whole concept of throwing a higher octane fuel onto the

onto the metabolism, that's not what's being picked up. You can drive more muscle glycogen, but you're just down-regulating fat metabolism as a result. So the overall ATP generation is the same throughout that, the different dosages of the carbohydrate that you're inputting into the system, if that makes sense.

Paul Warloski (20:30)

It does. so, you know, my question would be, if we are getting some kind of brain boost from the carbohydrate, the large amount of carbohydrate, what's the problem with that? But you said earlier that a lot of ingested glucose burns more glycogen. Am I hearing you right? And that's the downside.

Paul Laursen (20:56)

Right,

that's the downside. And that's not what we were taking carbohydrate in in the first place. And again, going to the Rothschild review, if we look at all of the studies, I think they reviewed 35 studies that actually measured muscle glycogen and carbohydrate dosing, it was about a wash, right? So there was, some studies showed a sparing and some studies show an enhanced burning of it.

When you think about the Bergstrom needle technique, ⁓ it's so variable, right? Like imagine taking a huge piece of meat out of your quadricept. This is what we're talking about, right? Just in one little area, usually on the vastus lateralis, and they go right in onto your vastus lateralis, take a little meaty piece out of there, and then they make all of their analyses. And that's what they...

That's the surrogate of all the muscle glycogen that's within your entire muscle bed. There's a lot of room for error there. You just think about it. Just to think that the total amount of glycogen that we're looking pre and post is just from that one single sample. And then we're going to try to put that back on the dose that we had. The noise is so heavy. And to actually find a signal in that noise.

Paul Warloski (21:58)

Hmm.

Paul Laursen (22:16)

I mean, just doesn't really make too much logical sense at the end of the day. So even the techniques that we've used to measure this is not ⁓ great, not doing research good justice at the end of the day. So let's call that a wash. Sorry, think I've washed your key question there, Paul, if I'm honest.

Paul Warloski (22:41)

The question was like, what's the harm then in doing more carbohydrates, but then the glycogen stores are getting used up more quickly because we're ingesting more carbohydrates.

Paul Laursen (22:54)

Yeah, I mean, and that's a really good question. So if we have studies showing that, which doesn't make intuitive first sense, why might that be the case? Why might more glycogen, why might the body change to burning more muscle glycogen as opposed to burning less, which we thought it would do in the first place? And the, we don't know, but ⁓ no one knows.

Paul Warloski (23:16)

Mm-hmm.

Paul Laursen (23:20)

but you could think of, there could be one reason, and that might be to lower the overall dose of glycemia that's in your body. Remember that glucose itself is a bit of a harmful and toxic substance, right? This is why we know that there's major problems with having a diabetic type profile, where you're always getting high spikes in blood glucose. This is why people wear

continuous blood glucose monitors to sometimes check this situation out. How am I responding to certain foods? I know the principle that I kind of want to have a stable blood glucose throughout my day because we know that tends to be associated with a healthier phenotype, the ability to burn fat more. ⁓ So in the case where, maybe it's the case that the body is trying to help you.

to lower your glycemic level. It's trying to lower that blood glucose level because it perceives it as being unhealthy. there's various different issues with all this chronic high glycemia and the toxic substances ultimately that it creates across the body as it melds into all the cells of the body. It doesn't like that.

Paul Warloski (24:19)

Hmm.

Paul Laursen (24:41)

and it creates harmful byproducts ultimately in your proteins of your body because of those. So, they're called advanced glycation endpoints, it's just come to me. So advanced glycation, glycation is the process of the proteins in the body becoming sort of full of carbohydrate and that glycation is what creates advanced aging in all of us.

Paul Warloski (24:47)

Interesting.

Paul Laursen (25:06)

So you don't wanna accelerate the aging of your body, you wanna lower that. So you lower that aging process by lowering your glycemia. So the hypothesis, the alternate hypothesis is that the reason the body is spinning higher amounts of carbohydrate burning from the glycogen is to, because it will lower the overall blood glucose. So, and in doing so, protect your cells from being...

undergoing that that glycemia, that glycation process.

Paul Warloski (25:38)

So there's actually a protective mechanism that's happening in your, is it in your blood?

Paul Laursen (25:44)

The protection is happening in the blood because the blood is going to all of the cells of the body. But the glucose, the large pool, the muscle glycogen is doing the job, right? And that's really the job of the muscles is you can almost think of it as a sink. It's a glucose sink. And it's sitting there and always taking up that blood glucose. So as opposed to, it's a different way of thinking. We used to think that the muscle glycogen

Paul Warloski (25:51)

Okay.

Paul Laursen (26:14)

was instrumental for eliciting prolonged endurance performance. And there's still a school of thought, there's the majority of us still think that way, but there's this alternate thinking hypothesis way that maybe the body of the large glucose pool, the muscle glycogen, is there more of a sink, a glucose sink that will always absorb up safely

that glucose to prevent the glycation issue that's going to advance our aging and therefore it protects the individual further.

Paul Warloski (26:55)

All right. I think I'm getting this. So the idea. Well, you're explaining it well. hope that there are hope our listeners are getting this as well. But for our listeners who are everyday athletes, mostly age groupers and masters athletes, what's the recommendation? Should they be trying to follow along with Sabastian Sawe did, you know, and get in 100 grams an hour for their workout? So what do you you're shaking your head? No.

Paul Laursen (26:57)

Good, I'm glad you are.

Well, I think that's the fundamental take-home message for the everyday athlete if you look at the New York Times article and many others that are basically pinning, they're pinning the performance not on this athlete's, you know, incredible training and preparation, the fact that this athlete has escaped hardships from Kenya and just, and the pressure to do this.

the incredible coaching that the coaching team has gone towards eliciting this. And the key things that wind up coming out as creating the performance poll are the two commercial entities. Number one, it's the shoes. It's the shoe technology. And number two, it's the fancy carbohydrate dosages of some unknown amount that are somehow

Paul Warloski (28:05)

Mm-hmm.

Paul Laursen (28:18)

allowing that enhanced, octane burn and not the athletes performance itself. And that in itself is a shame, in my opinion. So, and of course the natural lead on to that, is that we need to buy those shoes and we need to dose the high carbohydrates when we forgetting that that's the last thing you would ever add on to your performance.

Paul Warloski (28:33)

Mm-hmm.

Paul Laursen (28:43)

that what you want to do clearly is get back to basics and work on your training first and foremost and develop the aerobic foundation and the key sets that are going to, in a logical fashion, that are gonna start to build your own performance. the, yeah, if we're looking at the technological means of enhancing that, we're talking about the less than 1 % icing on the cake and that is the...

really a small portion of it all. You can certainly play with those dosages yourself. Be cautious, never would do that for the first time. The studies are very clear showing the numbers of reported incidents of high GI stress when high dosages of carbohydrate are taken on. That process may be able to be trained, but we're talking more in the, you know, the.

quite experienced, well-trained towards that elite level where that's gonna start to make a difference. And yeah, you're much more, you'd be much better off to use more conservative dosages that protect the small blood glucose pool, your brain's level of glycemia. So prevent hypoglycemia. That's all you need to do at the end of the day.

find the dose that helps that for you. I think what's really worked well for me, my colleague Dan Plews that set the Ironman world record in Kona, 50 grams an hour, was really good for something that's prolonged like an Ironman.

that works well for me. that even as a lower carb athlete, that's my own bias, that works well for me. That still feels like a lot for me, but when performance is on the line, I definitely go for around that level. And that's, that's fairly, that's relatively high. But I certainly wouldn't be doing, it were ever race matter, I certainly wouldn't be going down to 10, even though the study showed that with the Phil Prinz study.

The key thing with the Phil Prinz study was just to show the principle that you can, with such a low dose, you can still make a massive difference. So, yeah.

Paul Warloski (30:54)

what do you think is coming next? What kind of experiments do we need to figure out? the one question I have is there's still a pharmacological effect and what does that look like? But what do you see coming down the line with experiments and studies?

Paul Laursen (31:15)

Yeah, so I'm really privileged, Paul, to work with that great team that I've been mentioning in the podcast. And we have some really cool tracer studies that are going to be coming out probably within the next year that really confirm a lot of the stuff that I'm mentioning here today. we're not, once again, we're not seeing any dose effect of these high carb amounts right across from lowest to the highest.

you can imagine unless, you so it's in our data, we're not seeing that. that's gonna be coming out. And then I think we have to go, we have to dig deeper into the pharmacological slash drug effect that we've been speaking about, Paul. And that's because we cannot deny the fact that coaches and athletes are experiencing something special.

Paul Warloski (32:00)

Mm-hmm.

Paul Laursen (32:11)

to that they think is important to ⁓ elicit these performances. So we need to do more research that proves or disproves this pharmacological-like hypothesis. Maybe it's something, maybe it's not.

There's gonna be a lot of work that's gonna need to be done to design good studies that can tease this out to see if we're right. But at the end of the day, we can't say it's a high octane mechanism. It's an unknown mechanism at this time if there is indeed something that's out there. Don't forget also the power of the belief effect, right? If I believe that this is going to affect my performance, Paul, you're a...

Paul Warloski (32:54)

Mm-hmm.

Paul Laursen (32:58)

You're a coach, you put belief into your athletes before they're about to do the work, right? You give them all the confidence that they've done all that they can to elicit that performance on that day. And if that includes the intervention that we've been talking about, then that's another factor as well. So a lot of things that we don't know, and that's the fun of all of this, right? So we don't have to know it all.

Paul Warloski (33:02)

Mm-hmm.

Paul Laursen (33:27)

And despite what can sometimes be perceived as a lot of heatedness across the different areas in the debate, that's healthy because it's making all of us on both sides of the debate to think deeper. And that's what we have to keep doing. And that's the fun of science. We need to be true to the data, but humble enough to know that we don't know it all.

and then willing to do the work to continue to push our understanding forward. And that's what, again, I'm super proud of the entire team that I get to work with that has that same philosophy. They're not standing still. They're listening to all sides, and they're continuing to drive their understanding further.

Paul Warloski (34:14)

That seems like a good place to to wrap this up. there anything else you want to add to this discussion?

Paul Laursen (34:21)

I think we both nailed it, Paul. And I think that was, yeah, hopefully it's a complex topic with complex underpinning mechanisms. I did do my best to try to put it out there. It's certainly happy to do a coaching prof, a little newsletter on it with a little bit more insight and maybe some reading material that people can look at because sometimes we learn best by the combination of

Paul Warloski (34:36)

Mm-hmm.

Paul Laursen (34:46)

of both visual figures and then also listening to the podcast here. yeah, think it's a good spot to leave it though, Paul.

Paul Warloski (34:52)

Mm-hmm. Mm-hmm.

We look forward to a robust discussion on the forum and in our comment sections. Thanks for listening today to the Athletes Compass podcast. Take a moment now, subscribe, share, and let's keep navigating this endurance adventure together. Improve your training with the science-based training platform, Athletica, and join the conversation at the Athletica Forum. For Dr. Paul Laursen I'm Paul Warloski and this has been the Athletes Compass podcast. Thank you so much for listening.