"CHO Feeding Formats: Impact on CHO Oxidation During Exercise" with Dr Mark Hearris

EPISODE 173

[INTRODUCTION]

[00:00:01] LB: Welcome to episode 173 of The Institute of Performance Nutrition's We Do Science podcast. And I am Laurent Bannock, the host. Now, today, I just had a great conversation with Dr. Mark Harris, who has been on this podcast before where we talked about fuel for the work required. Carbohydrate, metabolism and exercise being a sort of a mainstay of his area of research interest. 

Also, Mark is one of our senior tutors here at The Institute of Performance Nutrition. I’m particularly excited to share Mark's knowledge with you on this really interesting and important topic. 

Recently, Mark and his team published a paper that essentially was looking at the comparable rates of exogenous carbohydrate oxidation and factors like the impact that that will have on endurance exercise, particularly cycling, GI discomfort, gastrointestinal discomfort, of course, from exogenous sources. Exogenous, obviously, being external. Supplemental sources, typically, like a drink, a gel, or a jelly. And these are all strategies that we've had around, of course, for a while. You'll see a lot of endurance, athletes, cyclists, runners in particular, using things like gels. They're not the only exogenous source of carbohydrate. You can get these drinks or foodstuffs in various formats. But they haven't necessarily been researched using things like isotope traces and blood work and so on, which Mark and his team have done in this particular study. 

It's particularly interesting to have a sort of a really good chat about what they found in their research and the wider body of knowledge as it were on this whole topic of supplemental carbohydrate intake, particularly from exogenous sources. And the relevance that that actually has on things like endurance and exercise performance. We talk about applicability to various levels of exercise, from amateur elite, to elite, of course. Translating the evidence into real-world practice can be complicated. We have a chat about that. 

And it's just really fascinating to hear about how these nutritional strategies can play a role in enhancing performance in general. We do, of course, talk about things like multiple transported carbohydrates and the various needs and preferences of different kinds of athletes, from liquid or solid form. 

Anyway, I know you're going to love this chat, particularly if you're a practitioner or researcher in this area and, of course, an athlete looking to use things like carbohydrate gels and drinks and so on. 

Before you get to listen to the discussion with Dr. Mark Harris, please check out our website at www.theiopn.com where you can find access to previous podcasts. The notes for this particular podcast and links to the paper in question and other relevant papers and podcasts and so on, I’ll put it all there. 

Also, please check out our advanced 100% online diploma in performance nutrition. There is no other program like it's. Entirely a unique science to practice focused program at the advanced level for current and aspiring sport and exercise nutritionists. If you're a sports scientist, strength and conditioning coach, you've already got your degrees in things like sports science, strength conditioning, nutrition dietetics and so on, this program will help you specialize in sport and exercise nutrition widely recognized. And many of our graduates are now working in elite sport and are very successful in private practice from the gym to bespoke performance nutrition practices around the world. 

You can also learn about our software, SENPRO. Designed entirely to support sport and exercise nutritionists and sports nutrition coaches in their work with individuals, with teams. Getting the absolute best that they can out of their athletes and their clients whilst minimizing administration. All the stuff that it takes to organize and control your clients. Behavior change, communication tools, nutrition periodization tools, all sorts of stuff. We keep upgrading the software. So please also check that out at www.theiopn.com. 

Anyway, that is all I wanted to say. Now, please enjoy my conversation with Dr. Mark Harris. 

[INTERVIEW]

[00:04:38] LB: So, hi and welcome back to The Institute of Performance Nutrition's We Do Science podcast. And today, it's great to invite back Dr. Mark Harris. Now, Mark, we know each other in a variety of capacities. You, of course, have been on this podcast before talking about not an unrelated topic that we're going to get into today, but of amongst your academic and research career. You're also one of our senior tutors on our IOPN diploma program. It's always an honor to have somebody like yourself on my team and have these kinds of conversations. It's just such a privilege to have that on the team, so to speak. 

Mark, for those that haven't necessarily managed to catch up with your last podcast yet, which I will link to, why don't you just give us a quick update? Because things are constantly evolving with you. Even I need to be uh brought up to date with you, mate.

[00:05:35] MH: Yeah. No. Thanks very much, first and foremost, Laurent, for the invite to come on. Like you said, it's always a pleasure to be invited on these sort of podcasts. I guess, really, the last time that we spoke, I was in the process of finishing up my PhD, which focused actually on what happens within the muscle when we restrict carbohydrate in and around exercise. 

I think, actually now, I’ve come full circle. And now I’m a postdoc still at Liverpool John Moores. But actually, looking at what happens when we feed a lot of carbohydrate in and around exercise. It's quite the polar opposite of the work I did during my PhD. But now our primary focus is looking at nutritional strategies to optimize carbohydrate availability in and around exercise with the ultimate goal of enhancing performance in the athletes that we work with. 

[00:06:31] LB: Awesome. There's a couple of topics that I guess are always hot topics. And for the many years now that I’ve done this podcast and for the – Well, I mean, the whole field of sports nutrition doesn't extend that much further than the podcast, really. I mean, it's been around for a while. It's still relatively new. I talk about this a lot with guest experts, how sport and excise nutrition is still pretty much the new kid on the block. Yes, we've got some other areas, sports psychology, and performance analysis and so on. But sport and exercise nutrition is exploding in not just its popularity amongst consumers, but also amongst researchers. 

And we only go back just a handful of years, and there would have been half as many sports nutrition master's degrees, a fraction of the publications that exist out there. And of course, you and your team at LJM, you have pumped out huge amounts of quality research. Many of your academic colleagues, of course, I’ve had here as guests on the podcast. 

This particular area is an area that I find fascinating, not just because it's hotly debated. There is a polarized debate on the topic of carbohydrates, principally, where it's attached to the whole-body composition conversation where some people believe that the consumption of carbohydrates has a particularly significant impact on body composition, which of course is completely lacking in any context, whatsoever. And we've discussed that a thousand times on this podcast. 

But when it comes to performance, carbohydrates are king. I don't believe there's any doubt about that. But of course, again, we can come back to a little bit of context. It does depend on what you're trying to do. And we've talked about that as it relates to carbohydrate ingestion through the diet, through supplementation, which we'll talk about a bit more today, exogenous sources of carbohydrates. And the intended purpose of that feeding strategy or that supplement strategy. Whether it's to influence impact training adaptations, or performance specifically on race day, game day, or whatever. 

But as always, what we need to do is dial back a bit and actually look at the evidence, look at the science, the physiology. Talk about the relevant context of application so that we all have enough information to understand this appropriately, accurately, robustly so that we can apply it into practice with the confidence that said strategy, said idea, said recommendation is actually going to do what we hope it will do in the appropriate place and time and blah blah blah. 

Anyway, look, you know more about this than me. But the reason why I reached out to you was because you just published – Your group and yourself, came out with this new study that largely relates to the impact of exogenous carbohydrate sources, which we'll simplify into supplements like drinks, jellies, chews, that sort of thing. But of course, we can talk about food sources and various other things that can achieve similar things, which of course we will get in today. But why did you do this research, Mark? I’d love to understand that first.

[00:09:57] MH: For us, the main idea behind looking at the different forms of carbohydrate came from a lot of field-based data that we know. That when endurance athletes are consuming carbohydrate in order to meet their carbohydrate requirements, they typically prefer to reach these requirements from a variety of different carbohydrate sources. A lot of the research today is typically done using liquid forms of carbohydrates. So, typical glucose, maltodextrin, fructose drinks. 

Well, like I said, we know from the field-based data that athletes typically like to use a mix-and-match approach where they will commonly consume combinations of all different formats in order to meet their carbohydrate fueling requirements. 

Really, for us, it was just about understanding how these different forms of carbohydrates are actually absorbed and oxidized within the muscle, and whether there are any potential differences in how they act within the body can have an impact on performance. 

I mean, we're definitely not the first people to do this type of study. [inaudible 00:11:10] probably over years ago now, looked at a number of different feeding formats. But I think one of the really nice novel aspects of this study is that we also adopted the mix-and-match approach that I’ve just spoke about. 

Actually, trying to understand what happens when you combine a number of these different carbohydrate sources together during an exercise bout, and whether they actually act the same as when you consume these forms independent of one another. 

[00:11:41] LB: There's so much there. You mentioned all sorts of words and phrases, which of course we love in sports science, sports nutrition. And there's a couple of areas, I think, that we need to sort of define a bit and unpack a little bit, because I think it'll make it easier for this discussion to filter across – Well, filter across between us, but also to the audience so they can get what we hope they do out of this conversation. 

You're talking about fuel. And we know, even if the only thing you've done is listen to this podcast, you would have heard people talk about fuel, and substrates, and so on. But of course, fuel isn't only carbohydrate. There are different types of fuel. And of course, there are different levels of intensity, different types of exercise, which I guess brings us to the sort of the type, the timing, the duration of both the exercise, but also the feeding strategy. 

I mean, this gets pretty complicated, Mark. And that's barely the tip of the iceberg. Perhaps we could go back to some basics here, if you could help us understand why we need to separate some of those things first before we start thinking about how all this stuff comes together as you've pointed out in these novel strategies. 

[00:12:52] MH: Yeah, you're absolutely right, Laurent. And I think it always comes back to your favorite word of content, right? And I think, first and foremost, before we'll able to make any sort of recommendations to our athletes, it's about actually understanding the physiological demands of whether it be the training that the athlete's performing, or actually the demands of the race. That's not always possible, because races are dependent on a number of different factors. But it's about trying to understand actually what are the physiological and metabolic demands of the type of exercise that we are performing. 

And really, until we have a good understanding of that, it's actually quite difficult to provide any bespoke fuel and recommendations without that sort of information. You're 100% right. I think there's more and more information now on the metabolic and the physiological demands of various sessions, of various different types of exercise, and of various different intensities and durations. 

I think, first and foremost, it's about understanding demands. And then once we have that information, we can then go on to provide some really specific nutritional recommendations to our athletes.

[00:14:10] LB: Yeah. I mean, in our previous podcast that we did, we focused on what is now – I hate to call it a catchphrase. But it is a good one, which is fuel for the work required. And that alone makes you think about, "Well, hang on. What fuel? What work? And how much is actually is required?" And in who anyway? Are we talking about sort of 12-year-old enthusiastic kids? I’m thinking about my own boys chasing around the house. There's fueling involved in that process. All the way up to when they grow up and become elite university athletes, which I’m sure they will do. And then fast forward into professional adult careers, potentially, as world-class Olympians. No pressure on my children, obviously. 

But there's a lot of different scenarios there. And of course, for one group of people, just "eating right" throughout the day would suffice. You don't need any specific strategies. Timing doesn't really make much difference for them. 

Whereas, bring this to, for example, one of the people you focused on in this new study, elite cyclists. And we'll unpack what that word elite means as well shortly. Where it absolutely can make a game-changing difference or a race-changing difference. Perhaps you could just explore that in a bit more detail, helping us understand the way the engine, if you like, uses fuel and stores fuel, and the variety of usage and storage mechanisms that are involved. Just a quick gloss over I think would help.

[00:15:45] MH: Yeah. For sure, you're right. And when we speak about the recreational athlete or just people who are typically exercisers, probably your primary concern is just to meet the day-to-day fuel requirements. And as you said, the specifics of that may not be of great importance. But I think when you get up to even in the amateur athletes, all the way up to the elite, the specific scenarios whereby the type and the timing of fuel intake, and also, the amount of fuel intake, of course, is our primary concern to them. 

I think that from what we know, you mentioned storage mechanisms of carbohydrate. What we know is that elite athletes, in particular, are very good at storing muscle glycogen. They have a higher capacity to store more carbohydrate. But the really cool thing about the elite athlete as well is actually the ability to use other fuel sources is a lot greater than your typical amateur recreational athlete. 

Even though the elites can actually store more of that carbohydrate, their actual relative usage of that carbohydrate is also reduced. When you think of it that way, it actually allows them to get through a lot more work compared with the recreational or the amateur athlete. 

But nonetheless, there is specific scenarios whereby the glycogen capacity of the muscle is still very limited even in the elite endurance athletes. And based on that information, we know that additional feeding of carbohydrate during the exercise by itself is important to not only improve. Well, not only to prolong that endurance performance, but also to actually improve the performance of that event as well.

[00:17:39] LB: Yeah. And I think that that's important. And, well, we have had conversations, you me and. I’ve had it with many other people about how strategic manipulation, i.e. feeding or restriction of carbohydrates, can result in either positive or negative adaptations, on training adaptations, of course, on performance. Even the link to the whole lactate issue with carbohydrate being involved in that. There are all sorts of stuff going on. And of course, there's those that are trying to go down the restriction of energy generally. And which macronutrient do you choose to restrict? And are you an endurance athlete? Are we trying to improve mitochondrial biogenesis? Do we want to become more efficient? Are we trying to train low-train heights? These are all previous conversations that we had. 

But I think fast forwarding to this very concept of feeding strategies as a strategy, and the usage of novel sources, i.e. food, or manufactured foods, or supplements as we call them, in very specific scenarios is the area that I think this particular research and this particular conversation is really what we're going to be focusing on just so that everyone's particularly clear about what angle we're having here.

And of course, we can look at the strategies and we can look at supplements as tools in the toolbox. Another phrase I like to use. Why, Mark, do we want to have different tools in our toolbox for this sort of thing? Why didn't you just look at drinks, for example? Why did you look at a mixture of different strategies there? Feeding forms? 

[00:19:24] MH: It's a great point. I mean, as I mentioned briefly before, I think the main reason for this is because this is typically what we see endurance athletes doing. We don't typically see that these athletes are relying on one particular source, for example, drinks, as you just mentioned. They do self-select a variety of different feeding formats in order to meet these demands. 

And if you think about it, it makes sense. If you're riding on your bike for three to five hours, then the last thing that you want to be doing is consuming exactly the same thing across that for a long period of time. I think, for a lot of these athletes, these practices that they already habitually perform actually just comes from their own particular preference. Some athletes might have a preference for drinks. Some might have a preference for solid foods, as you mentioned. And then other athletes, a lot of them that we see, like to adopt this mix-and-match approach where they have a variety of different sources. 

I think, just purely, to avoid any sort of boredom and fatigue of that particular thing, the important thing to remember is that the primary objective here is to maintain the ability to keep ingesting large quantities of carbohydrate. And if, actually, the form of carbohydrate that you're consuming is having a negative impact on that, whereby you've taken nine gels across three hours. Probably the last thing that you want to do is to have another gel, right? 

I think the ability to be able to mix and match across these different formats is something that these athletes really benefit from in order to able to maintain the ability to keep consuming carbohydrate.

[00:21:16] LB: Absolutely. Now, just because people take these things does not mean that they need them though, does it, Mark? Should we look at that first? Because, obviously, if you go – I remember when I used to live in London and I was riding around Regents Park, for example, or Richmond Park, and you've got your sort of amateur triathletes, people training for their 5ks, and 10ks, and so on. You'd see people just pumping themselves with energy drinks. A bit like a sort of an old-fashioned American cowboy movie. You'd see them with like bullet belts. Just stuffed full of gels, up the arm, across the chest, taped all over the handle bars in bikes. Just covered in these supplements. And a casual look at the rider, and obviously, these aren't elites for the most part, could lose a few pounds themselves. At what point do we go from not needing it to needing it, Mark?

[00:22:14] MH: Yeah. It's a great point. And it really comes back to like we said before, trying to understand the physiological and the metabolic demands of the session that we're performing. 

I mean, I think if you look at the ACSM guidelines, anything under 60 minutes, you probably don't really need any sort of form of additional carbohydrate. Like I said before, we are able to obviously store carbohydrate within both the liver and the muscle. And then stores, albeit, the fact that they are limited, they do provide sufficient energy for quite short periods of exercise, up to 60 minutes. 

Anything above 60 minutes to around about two, two and a half hours, the guidelines suggest between and 30 grams of 60 carbohydrate an hour. And then I guess anything above two and a half hours onwards, the guidelines recommend 90 grams an hour, or 60 to 90 grams an hour, all the way up to probably the upper limit of recommendations, which is around about 120 grams, which is what we actually studied in the present study. 

[00:23:23] LB: And to differentiate enthusiastic cyclists, for example, from a pretty serious, but nonetheless amateur triathlete, to a world-class professional rider, or world-class Olympic triathlete, for example, what sort of variations are likely to exist there in terms of need? 

[00:23:42] MH: Yeah. I mean, that's a great point. Like we said before, obviously, elite athletes have a greater ability to store glycogen. You'd argue that they could, I guess, go longer without any exogenous forms of carbohydrate intake. But I actually think between the standard of athlete, if you like, it more boils down to than metabolic demands. Because if someone's exercising at an intensity that requires a certain amount of carbohydrate, obviously, for the elite, that would occur at a much higher running speed or a much greater power output. 

But I think, relative to the individual's ability, it's really just about understanding the metabolic requirements. Even if you've got a higher standard athlete, but they're exercising at a really low-intensity, then obviously the requirements for carbohydrate will still be low regardless of the fact that whether they are elite or not. 

[00:24:48] LB: Yeah. If your efforts are ambitious in terms of how long your ride or your run, for example, is going to be, then you get an increasing sort of argument in the direction of these things have a value. And I guess that's what we're trying to arrive at here, is one's interpretation of what that value is. How you manage the expectations of the value that you derive from these supplementations? And then, of course, well, which ones do you take anyway? And then how do you maximize the return on your investment in these products, because you have to buy them, of course, one way or the other. 

I know we want to get a lot into the applied side of this. Ultimately, it's how can you take advantage of these products. You did this study. There are other studies that have contributed to this body of knowledge on the need for carbohydrate supplementation, exogenous carbohydrate intake in various forms. But not all those studies have been done the same way. Varying levels – Well, I mean, we've talked about this 70 so many times about quantity versus quality in the sports science realm as it comes to scientific publications. But there's a big difference in how some studies are done. 

And you guys at LJM, have some incredible facilities for your research. Perhaps you could just give us a quick overview behind the study that you did so that we can understand just how it is you arrived at the findings and conclusions that that came from that.

[00:26:25] MH: In my point of view, I think what's really cool about the study, and it's the first time that actually this is being done across multiple different feeding formats, is that we're really lucky with our funders at science and sport. That we have a great MPD technology team which actually allow us to create these products particularly for scientific research. 

I think a lot of other research trials that study these different things actually just use either homemade kind of recipes or off-the-shelf recipes if you like. But I think what we're really lucky to have is a great technology team, which actually allowed us to incorporate the stable isotopes that we use to measure the oxidation of the ingested carbohydrate into each and every one of these feeding formats. And that's the first time this has actually been done across. It's been done in drinks multiple times before for over 20 years. But actually, incorporating these stable isotopes into the gel. And the jelly chew format is something that I think is is really novel in the study. And it actually allows us to accurately quantify the oxidation of these formats without relying on – What most people use is the natural enrichment of various off-the-shelf products. 

I think it's really cool that we're able to do that in this study. And like I said, it's the first time that this is actually being done across multiple feeding formats within the same study. 

[00:28:06] LB: Mark, look, you're a busy man. You've got a lot of stuff going on. Why make your life that much more challenging by throwing all this extra stuff in looking at isotopes, looking at blood sampling, a whole range of metabolic testing protocols, finding decent athletes, that sort of thing? I mean, why not just come up with a much simpler study? Arrive at those conclusions a lot more easily. And, "Boom! Here's your outcomes." I mean, why go to that level? Why is it important, Mark? 

[00:28:36] MH: Yeah, it's a good question. It definitely would have saved me a lot of sleepless nights doing something a little bit different. But I think, for us, it's all about research quality. And it's about arriving at findings that you can truly trust and you can truly believe in. 

I think, for us, it's about understanding the whole picture. I think without some of these techniques that we use or some of the different sampling methods that we use, it's almost like you get half of the answer. 

I think once you incorporate different methodologies and different techniques, it allows you to just gain a real insight into actually – Like I mentioned before, the metabolic and the physiological demands of these types of sessions. And actually, really just understand, specifically in this scenario, when we're looking at the oxidation of the ingested carbohydrate. I don't think it's really enough to just look at whole body substrate where we're saying carbohydrate, whole body carbohydrate, oxidation might change across formats. It's really important to actually label these substrates with the traces in order to actually specifically understand how much of that ingested carbohydrate is being oxidized. Yeah, I think it's just about research quality and getting the most out of the study that you can do really, Laurent. 

[00:30:08] LB: Yeah. And that's great. I think it's awesome you guys are doing that. If I change hats to being a practitioner working with many elite athletes over the years, not so much cyclists, but football being a big area. I know you're going to be doing a study in – Or you've just started another study in a similar vein, but with football players. This stuff is important. 

And I know there are a number of listeners who aren't sports scientists or nutritionists, but they are high-level athletes who love to geek out on this stuff. And of course, this makes a big difference to to them or to us advising them. If we're telling them to do things that's based on very loose assumptions, and the reality is it may, may not work, at least not in the ways in which we were thinking it was going to work. And the consequence, of course, is not achieving the level of performance at best or at worst, problems with their health, or accidents, or whatever can occur. This stuff really matters. 

And I think even for the casual consumer, where those things may not be a risk to them, they are wasting time and money, if nothing else. The sports nutrition commercial market is massive. And I guess some people would say, "Well, but this study was funded by," as you say, "science and sport." You and I know that's ridiculous, because a quality study with the right scientist and published in the right journals with the appropriate level of peer review and so on is the filter that's necessary to differentiate quality from poor or really bad science. But again, maybe you could just explain why that was important for you guys to go through that level of rigor with this.

[00:31:50] MH: Yeah. I agree. You hear a lot of people saying when they look at the funding organizations for different studies, that, "Oh, can you trust it?" And so on and so forth. And a lot of researchers come back with the same answer is the fact that you need the funding organizations to be able to do this. And without it, these type of studies and this type of information wouldn't be possible. 

I think, like you said, it's important that it goes through that rigorous process when you're designing your methodology. But also, that rigorous process of peer review to know that when you're actually reading a publication and you're looking at the data that it's gone through the process and you can actually trust the information that you're reading. 

[00:32:43] LB: Well, also, the information helps inform the manufacturing process by – For example, this is science and sports. They're investing obviously in trying to produce the best products they possibly can, because it matters to them that the products actually work. Given so many elite athletes use their products. 

And really, what I was saying is it's just so many nutritional products exist out there that really have a very weak, or none at all, in terms of evidence to support their use. Because one of the questions that, of course, will come up with, "Why would I take these products?" As opposed to consuming a banana or consuming a sandwich, Mark? Why jump that bridge? The gap that exists between foods that we will generally find in our fridges, in our larders, in a normal supermarket, as opposed to these very much designed products that are existing? What your view on that? 

[00:33:46] MH: Yeah. I think it really comes down to the specific scenario that you're working with. For sure, there's a number of different foods or whole foods that are ready available for people when perhaps they're going out on a really easy training ride or a really easy recovery ride, whereby they can pick up a variety of these different whole foods and they can take them on the bike with them. And there's probably no issues with people doing that. 

I think the scenario in which you need these real bespoke supplements, if you like, is where – It's probably primarily in racing scenarios, whereby you need to know that everything that you are putting in your body is going to work exactly how you want it to work. And there's a lot of differences between being on an easy recovery ride compared to when you're at kind of top-end speeds, you're really pushing. There's a lot of other factors that come into racing. Things like anxiety that can obviously impact our gastrointestinal system. 

I think what's really nice about this study is the fact that, like you mentioned before, these are actually products that are now commercially available. And the reason why science and sport was so invested in this is to actually have real research backing behind products that you can actually pick up off-the-shelf. And there's real strong evidence behind them that you know exactly how they are going to work and exactly how they'll be oxidized within the muscle. 

I think for a consumer, it's really nice to just have that peace of mind that actually these products have been extensively researched. And here's the data on this. And you can go and make your own mind whether this fits into your nutritional strategy or not. 

[00:35:50] LB: Yeah, yeah. I think, look, we've already mentioned the evidence is extremely robust when it comes to showing the value of carbohydrate in relevant areas of performance, particularly where winning races, etc., are going to matter then it is something you're going to want to take seriously. I appreciate if we're looking at things like ultra-endurance, multi-stage ultra-endurance events. There might be different approaches to that, which we've talked about in the previous podcasts. But for things like cycling, and long-distance running, and so on, when you look at the elite athletes, or elite amateur athletes, they're moving pretty fast. That mixture of fuel that's being used is very much dependent on the access to carbohydrates. That's what I wanted to bring us to. 

You use words like endogenous and exogenous carbohydrate oxidation. And you've given us an idea about the value of that, particularly about exogenous carbohydrate oxidation. And that brings us to these novel products and so on. And of course, there are many choices. Some of which would come down to preference, taste, practicality, all those things that we can argue in favor of taking these products. But what did you find in your research as it relates to the different types of drinks, chews, etc., that you looked at? And what did you learn from that research? 

[00:37:19] MH: The main outcome variable that we measured across our study was, like we've mentioned before, the oxidation of the ingested carbohydrate. That's essentially how much of the ingested carbohydrate was actually being oxidized within the muscle to fuel the exercise, if you like. 

And what we're seeing is that, across each of the different feeding formats, and even when you co-ingest all of these different feeding formats together, they're all oxidized at pretty much the same rate. I think that sends a really nice message to all of the endurance athletes out there. 

And like I mentioned earlier, a lot of these guys are already following this mix-and-match approach, whereby they co-ingest in different forms of carbohydrate. This really just supports the habitual behavior, what they're already doing on the bike. To tell them that regardless of the format, as long as you meet your carbohydrate fueling requirements, whether it's on the bike, or during a run, or whatever it is, you can pretty much choose the feeding format that matches your preference, matches the race conditions. Whatever it may be, it just gives you a little bit more freedom in order to pick your fueling requirement based on, like we mentioned before, the intensity and the duration of the exercise being performed.

[00:38:47] LB: Thanks for that. Look, when we look at this from the lens of a researcher from the perspective of metabolism, it's a biochemistry conversation that we could be having and have had. But we are talking about human beings in the real world. And yes, we've talked about practicality being an issue. One issue that has reared its ugly head over the years, of course, is this whole area of gastrointestinal discomfort, which can really be a real problem for – I mean, it's more than just a very small number of people. I mean, it is an issue that occurs a lot, which is an argument for these products. And also, the limits to the amount of this fuel that you can essentially consume, which causes a number of problems in itself. Maybe you could just quickly talk about that, particularly from a gastrointestinal discomfort perspective.

[00:39:44] MH: Yeah, you're absolutely right. I mean, there's a lot of you know field-based data out there now that shows that gastrointestinal problems can be a real issue during prolonged endurance events. And I think when we speak about these different ranges of carbohydrate requirements during exercise itself, I think it's really about finding a balance between – Or maximizing the oxidation of ingested carbohydrate while also minimizing the amount of gastrointestinal distress that we suffer from. It's definitely a real balance and definitely something that requires practice to kind of understand where an athlete's optimal carbohydrate intake requirements are. 

But I think one of the main issues with some different carbohydrate products or different carbohydrate formats in different conditions is that if you're not able to oxidize a lot of the carbohydrate that you're being ingested, there's probably one major site where that remaining carbohydrate is sitting. And that's within the intestine, predominantly.

And if you think about it, that's the main major cause of this gastrointestinal distress. Because if you actually can't absorb that carbohydrate through the intestine, into the liver, into the circulation, and ultimately into the muscle to be oxidized, then any of that remaining residual carbohydrate just sits in the gastrointestinal system. And over multiple hours of exercise, that's just going to build and build and build. And ultimately, that might be the difference between you actually just finishing the race or not. 

I think it's definitely a real important consideration. There's no point consuming X amount of carbohydrate if it's going to cause you a lot of gastrointestinal distress. It's about really trying to find that balance of how much can I consume whilst minimizing any sort of gastrointestinal distress?

[00:41:57] LB: Absolutely. Yeah. And there's some very interesting research that goes into this that relates to different types of athletes. For example, if you're into foot racing, for example, there are additional impacts on the gut potentially from the sheer impact involved in running, relative to the weight-bearing advantage, if you like, in that regard for being on a bike, which all factors in. Of course, this all gets rather complex, which is why one has to consider the individual needs and preferences and so on. 

But what about this idea that, in conversation, scientific conversations, you tend to reduce things to terms like carbohydrates. But there are different kinds of carbohydrates, and obviously different sources of carbohydrates. Why does it matter that we do also factor in the types and sources of carbohydrates that are found in these products? What are your thoughts and findings on that? 

[00:42:55] MH: Yeah, it's a great question. And in terms of carbohydrate, in terms of type of carbohydrate, you're absolutely right. The type of carbohydrate that we consume can have a huge effect on the amount of that carbohydrate we can actually absorb. 

The main reason for this is that there's two main types of carbohydrate transporter within the intestine. And these transporters actually become saturated at different quantities of ingestion. For example, the glucose transporter becomes saturated in and around 60 grams an hour. For example, if you put a lot more glucose in than 60 grams an hour, you still won't oxidize any more of that additional carbohydrate that you've put in, if you like. 

And to go back to the point I’ve just mentioned, if that continually builds up and sits within the intestine over multiple hours, it's pretty much likely that you're going to suffer with some sort of gastrointestinal distress. What you can do in order to circumvent that is use a different type or co-ingest a different type of carbohydrate with that glucose. Typically, that is fructose, which uses a different transporter protein. And that actually allows you to ingest a lot more carbohydrate than the 60 grams of glucose that you can consume. 

In this particular study, we use the combination of either maltodextrin or glucose, which is obviously such or used by one transporter. And then the additional carbohydrate came from fructose, which allows us to take advantage of the other transporter and actually push that rate of ingestion all the way up to 120 grams an hour. 

[00:44:51] LB: This metabolic machinery that revolves around fuel or substrate utilization, processing, if you like, that sort of thing, do we all start off with the same kit so to speak? Does that require training like our muscles need training? Muscles, fibers and so on? We've had these conversations with yourself and other experts about the sort of the role of training the gut, for example, as it relates to gastrointestinal discomfort. We know that different types and timing and duration of training will have different impacts on training adaptations and so on. What about on these transporter mechanisms and our ability to actually take up and draw down on these fuel supplies? What about that side of things? 

[00:45:38] MH: Yeah. I think the whole concept of training the gut is really quite a hot concept at the minute. And it makes absolute sense. If you expose these transporter proteins to the substrate that they carry over a long period of time, then of course it makes sense that you're going to upregulate the amount of these proteins that you have. 

We don't actually have real direct evidence. Because, obviously, taking tissue samples along the gastrointestinal system comes with its own problems. But of course, it makes absolute sense that that would occur. We do have some, I guess, indirect evidence of that that shows that I think some work from Greg Clarkson. And actually, you can drop that it's 10 probably over years old now that shows that daily training or consuming carbohydrate during every single training session actually increases our ability to oxidize a set amount of carbohydrate, which is really cool, right? Because if we can increase our efficiency to oxidize ingested carbohydrate, not only does that give us more available substrate during exercise itself. But it actually also reduces the amount of residual carbohydrate that is sat within the gut. 

And I guess as a secondary benefit, potentially, will also reduce any gastrointestinal symptoms. And over the past, I think, five years, there's been some cool data to show what they call repetitive gut challenges. So, repeatedly challenging the gut with high amounts of carbohydrate does actually improve some of these gastrointestinal symptoms that we see during exercise. 

I think, absolutely, it makes sense to start thinking about how we can begin to train the gut. And also, I think it just makes sense from a practical point of view just to be able to practice consuming carbohydrate. And not only carbohydrate, but fluids also, the process of drinking during exercise when we've obviously got high ventilatory rates and things like that. I think when taken together, it makes absolute sense.

[00:47:57] LB: Yeah, of course, you can package these things with caffeine, with electrolytes, like you said, liquid water, that sort of thing. But again, we come back to this choice that people have. And there's nothing like giving people too much choice to induce huge amounts of anxiety, particularly in elite athletes, who just want to know the best answer, "How do I win that race? Just tell me what to do, Mark." 

You've got drinks, you've got gels, you've got jellies. You've mentioned that, one way or the other, they're all going to provide the support that the ingester is requiring. Yes, you've got individual taste and so on. But what about this congestion approach idea? Or is that just the same? It's like whatever you like doing the most. Is that how that works? 

[00:48:44] MH: Pretty much, yeah. The co-ingestion approach that we used was essentially during the three hours of exercise. Subjects will consume a combination of – Or an equal combination of carbohydrate from the drink, from the gel, and from the jelly chew. 40 grams of carbohydrate per hour would come from each of the individual's sources. Given a total of 120 grams per hour. 

That was really just to show that, "Okay, when we test these formats, I guess, independently of one another, they are all locked similarly." But what happens when we follow the habitual feed and practices of these athletes? And we almost throw them all together, if you like, and they all mix within the stomach. Is there any sort of issues that are caused by that strategy? 

And again, from the data that we've got, you can see that not only are they oxidized at very similar rates to all the format independently. But again, we report very, very trivial, if not any, gastrointestinal symptoms from that approach too. 

[00:49:58] LB: Now, not all products are created the same, obviously. I say obviously. Not everyone realizes that. They will find themselves presented with products that essentially look like gels, look like jelly chews, look like drinks. But they do come in slightly different ratios in terms of the formulation of the basic ingredients. What's are the sorts of things that you need to be looking for? What does the evidence tell us seems to be the right combination of products?

[00:50:33] MH: Yes, it's a great question. And there's been a lot of independent study on the different ratios of carbohydrate. The general consensus seems to be that a ratio of 1 to .08 of maltodextrin or glucose to fructose is pretty much the optimal ratio in terms of being able to oxidize the most of the ingested carbohydrates. I think the studies, or the older studies that have been done, typically used a two-to-one ratio. Typically, that would be, for example, 60 grams of glucose and half of the amount of fructose, 30 grams of fructose. 

The more recent evidence, like I said, seems to be that when you ingest that ratios closer to unity, where the maltodextrin and fructose are very similar. At least when you're ingesting high quantities at or above 90 grams an hour, the optimal ratio seems to be one to around about .8.

[00:51:42] LB: We have a number there, which is the rate of at or above 90 grams per hour, which has been shown to allow for higher rates of oxidation during exercise. But how about this idea of more is better? Is that the case? How should individuals be looking at this advice?

[00:52:03] MH: Yeah. I mean, I think you see that with any sort of nutritional strategy or supplement, don't you, of people? I guess the message is sometimes more is better. But that's definitely not the case. I mean, like I said before, it's definitely a balancing act between how much can I maximally oxidize against what's the maximal dose I can consume without reporting any gastrointestinal symptoms? 

As far as I’m aware, the maximal oxidation rates have come from the ingestion of 2.4 grams of carbohydrate per minute. I think that works out at about 144 grams per hour, which is obviously a hell of a lot. That seems to be – Well, that's probably the highest oxidation rates that we've seen in the literature. And this definitely becomes a saturation point, whereby the rate limiting step seems to be the absorption through the intestine. 

But I think there must also be a point where there's a limitation at the level of the muscle, whereby we can actually not take any further carbohydrate from the circulation. And that seems to be around about that value that I’ve just said. I think around about 120 to 140 grams an hour. I think we're probably looking at a ceiling for intake or ingestion rates in and around 120 grams an hour, there or thereabouts. 

[00:53:41] LB: Yeah. Of course, look, a lot of this is going to come down to practice with it. Try it. It's a proven strategy. It's not going to work for everyone on the basis of not everyone actually needs to be doing this. But a lot of people will benefit from it as this research and other research has clearly pointed out. 

If we just move to some practical aspects here, we're using terms like feeding strategies, 90 to 120 grams per hour, blah, blah, blah, blah, blah. Maybe you could just illustrate some examples? I mean, obviously the context is more endurance racing type events that you're more focused on here. 

I mean, what are the areas of application you see this having particular value? And what is the range? We've used terms like athlete, and elite and so. I know we've briefly touched on this. But it would be good as we draw this conversation to a conclusion. It'd be good to just quickly talk about that.

[00:54:41] MH: Yeah. I mean, I think if we go back to some of the ACSM guidelines, like I said before. Typically, endurance events at or above two and a half hours is where you see these recommendations of 90 grams and above, 90 grams an hour and above. 

I think in terms of exercise duration, somewhere in and around that ballpark. Again, when you look at exercise intensity, it's important that it's of sufficient intensity to actually require this amount of carbohydrate. I think if you are an athlete or an exerciser who is running, or cycling at a relatively low-intensity, your overall – Not only energy requirements. But your overall carbohydrate requirements might not actually be that high. There's no point feeding two grams of carbohydrate a minute if you're only oxidizing at levels below that. It's just going to be a waste of time and money for yourself. 

It has to be an intensity – Of sufficient intensity to require this amount of carbohydrate. But I think like we touched on before, the level of athlete is, I guess, less of a influencing factor in this. Because as long as it is of sufficient intensity and duration for that specific individual, then these requirements will pretty much apply across the whole spectrum of athlete.

[00:56:22] LB: Yeah. No. Brilliant. Yeah. I mean, look, I’ve mentioned before. We've done a podcast before about this idea of fueling for the work required. I think it's necessary to re-listen to that podcast. I’ve had similar conversations, of course, James Morton. Very first ever podcast. We touched upon this course years ago now, which James has done a lot of work in that obviously. And Trent Stellingwerff, and so on. We talked a lot of the applied aspects of this. 

But it's really interesting, as sport and exercise nutrition continues to grow and develop in terms of the research that adds to the body of knowledge. And ultimately, informs the decisions we make as practitioners or researchers and so on. Obviously, that filters down to consumers, which is why this sort of conversation has its value across all of those stakeholders, is because there are a lot of people buying stuff they don't need and/or aren't using properly. And it's like tools, generally, isn't it? In the right hands, they can be of great value. In the wrong hands, they can cause a lot of damage.

But look. Listen, Mark. I mean, it's been awesome to have this conversation with you. Everyone obviously should read the study. And just quickly, future directions in this area? You mentioned your offer in particular. But you're just broken ground on another study with football players, I think? Where's all this leading towards, you think?

[00:57:40] MH: Yeah, that's right. I mean, I think, like I mentioned at the start. Our main focus of research within our group is to look at maximizing the availability of carbohydrate in and around exercise. And whether that'd be endurance exercise or team sport exercise. I think there's a lot of different applications for this. 

I think also, moving forward the field can definitely learn a lot more from the whole topic of training the gut. I think that there's a lot of work to be done in that area to actually understand what is happening. How can we do this? What's the best strategy to do this? And actually, potentially even the time course of these adaptations. How long do we actually need to train the gut? Because that's obviously got implications for people's preparation for these different type of events. Hopefully, there's a lot more work to come from us. And hopefully, it won't be too long in the making. 

[00:58:39] LB: You're not going to be bored for a very long time, Mark. I can tell. But no, in all seriousness, it is fascinating. Whether you're a practitioner, researcher, or a consumer of this information, there's just no question the value that sport and exercise nutrition, diet, feeding strategies, etc., etc., can have. And we're going to see more and more, obviously, ideas, and strategies, and tools and so on coming out in the future. 

Thank you for your contributions to the research on that side, you and your colleagues. If people want to follow your work as a researcher, etc., what's the best way of people following you, Mark? 

[00:59:24] MH: Yeah. People can follow me on ResearchGate. And they can see all our updated work on there. I have to confess, I’m not the biggest user on social media. But any studies that we do publish or any other work that we have on there, you can also find on my Twitter page as well. 

[00:59:42] LB: Well, that's because you're too busy, Mark. That's why. Good man. Yeah. Of course, also, our students are very lucky to learn from you as one of our awesome tutors on our tutoring team at the IOPN. Thanks for that too, Mark. 

Well, look. Thank you for your time. That's it. We've had a great conversation. And I guess I’ll be seeing you in a team meeting on another occasion. 

[01:00:02] MH: Yeah, thanks very much for having me, Laurent. 

[01:00:04] LB: Great stuff. Thank you.

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