Episode 164 - The carbohydrate advantage: Can more carbs help you go the distance?

The carbohydrate advantage: Can more carbs help you go the distance?

Carbohydrates and fats are the body’s main sources of energy in endurance sports, and getting them right can make or break your race day.

That’s why I invited Sam Shepard, a researcher and fellow nutrition enthusiast, onto the TNA podcast to discuss the science of energy production and how you can use it to perform at your best. There’s a lot to unpack here, so we’re breaking the conversation into two episodes. This week, we’re focusing on carbohydrates, and next week, we’ll dive into fats.

Sam begins by sharing studies on the oxidation of carbohydrates and fats during endurance events. These studies show that carbohydrates are the body’s primary fuel source early on, but after about two hours, fats take the lead. Understanding this can help us make better fuelling choices. However, like all things in sports nutrition, there are many factors to consider.

 

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Episode Transcription

Episode 164: The carbohydrate advantage: Can more carbs help you go the distance?

Welcome to the Triathlon Nutrition Academy podcast. The show designed to serve you up evidence-based sports nutrition advice from the experts. Hi, I'm your host Taryn, Accredited Practicing Dietitian, Advanced Sports Dietitian and founder of Dietitian Approved. Listen as I break down the latest evidence to give you practical, easy-to-digest strategies to train hard, recover faster and perform at your best. You have so much potential, and I want to help you unlock that with the power of nutrition. Let's get into it.

 

[00:00:20] Taryn: Joining me on the podcast today is researcher and fellow nutrition nerd, Sam Shepard from all the way in the UK. Welcome Sam.

[00:00:29] Sam: Hello. Hello. Yeah, can't say it's nice and sunny here, unfortunately, but yeah, we're heading into winter. So there you go. And I'm, British. So I'll immediately start talking about the weather because that's what we love to talk about. So, but yeah, thanks for having me.

[00:00:41] Taryn: Oh, so funny. You're welcome. We are talking at my night time, your morning time, because that's what we do. The time difference between Australia and the UK sucks balls. So apologies if my voice gets croakier and croakier as we go, but Sam has promised to bring the energy, even though he's British, we won't hold that against him.

[00:01:03] Taryn: And I did speak to my husband just before, who's in London at the moment. And he showed me the sky and it was great and it was dreary, but you know, that's a, just a regular day in London.

[00:01:13] Sam: Absolutely. Absolutely.

[00:01:15] Taryn: So Sam has agreed to come and talk to us on the podcast all about carbohydrate and fat oxidation. Oh yeah, we're going to get down and dirty in the good stuff. He has recently taken on a role and is now the head of sports science at Precision Fuel and Hydration, which is very exciting. But his background is, oh God, how many years of study have you done, Sam?

[00:01:35] Taryn: Like 50 million.

[00:01:36] Sam: Uh, , so yeah, undergraduate masters PhD. So that's probably about eight years altogether. And then yeah, 12 years in academia. Before making the switch to sort of industry, I suppose.

[00:01:49] Taryn: Yeah, total nerd. I love it. And that's like a term of endearment, right? Videos. 60 publications to his name in what I would say is the most varied range of topics I've ever seen anyone research in. He calls himself a jack of all trades because he's got stuff in like lipid metabolism, Glucose Oxidation, Diabetes, Obesity, Cardiorespiratory stuff, Insulin Resistance, like what else?

[00:02:17] Taryn: All the things.

[00:02:18] Sam: all the things, yeah. I mean, I suppose everything that underpins this is my interest in metabolism, exercise metabolism. And then it's just the application of that is what I would like to say.

[00:02:30] Taryn: Yeah, and you have a particular interest in something very, very nerdy that you tell me only four people in the world are interested in. Could you please explain that a little bit?

[00:02:40] Sam: Yeah, so, I suppose it started in my PhD and then I, you know, I've been doing this type of work for probably, yeah, up until the sort of last couple of years, really. when I was doing my PhD, we were really interested in lipid droplets or fat droplets in muscle and how that's related to insulin resistance, but also how it's related to health.

[00:03:00] Sam: So there's something called the athlete's paradox where. if you're very healthy, you'll have a lot of fat in your muscle, but it's a substrate as well, which we'll kind of come on to through this podcast. But in a sedentary person, when they're insulin resistant obese or type 2 diabetic, then they also have a lot of fat, but it's just not usable.

[00:03:19] Sam: It's not particularly metabolic. And so that relates to the relative insulin resistance that those people experience. And so, my interest in my PhD was working out why that was, what are the proteins that are linked to these lipid droplets in muscle, using microscopes to, to like, look at like muscle samples that we've taken out of all sorts of people.

[00:03:37] Sam: And like nice colorful pictures, which are great when you go to conferences and you can put them up and everyone goes, Oh, wow. one of my PhD students actually termed it disco muscle, which I thought was really nice. way of putting it. So, yeah, there's probably only about me and about four or five people in the world that really nerd out on that.

[00:03:53] Taryn: And look how excited you get talking about it

[00:03:55] Taryn: too. You're like, yes, let's go. Somebody asked me a question.

[00:03:58] Sam: yeah, 

[00:03:59] Taryn: Other than being a researcher weapon and lover of all things science, he's also a little bit of a weapon on the triathlon course.

[00:04:07] Taryn: Sam was the overall winner of a full distance event in Majorca in 2021. He beat all the men, all the pro men, I might add. What time did you do for that race, Sam? I

[00:04:19] Sam: Oh, it wasn't a quick one because it was so hot. So I was just the sort of last man standing. I think more than like taking the win. thought. There you go. That we can talk about, you know, heat acclimation and the importance of monitoring your workload in the heat. And I will say that's what I managed to do that day better than 

[00:04:34] Sam: the others. 

[00:04:35] Sam: to come through. 

[00:04:35] Taryn: well done. well done. his fastest Ironman or full distance race time is 8. 45 at that same race the year later. Like so it's, you know, it's not something to be sneezed at, that's a relatively fast full distance race.

[00:04:51] Sam: Yeah, not too bad. So, I mean, hopefully we can get somewhere close to it next year. Uh, I actually did Talon Ironman in 2021 as well, and I went 9. 01. So I've got a bit of I need to go back and get sort of 9 there. Maybe that's the plan for next year.

[00:05:04] Taryn: And you have been to Kona the year after that, 2022. Is the plan to go back to Kona again?

[00:05:10] Sam: that'd be nice. Hopefully 26, especially having just watched it this weekend and getting very excited about it. As always I think that's what I, grew up remembering.

[00:05:18] Sam: And that's probably my first recollection of seeing these guys on this like nice, you know, Hawaii, a nice island. Doing something absolutely crazy. Yeah, and it's yeah, it's just growing from there really

[00:05:29] Taryn: It is such a cool event and you've proved that you can perform in the heat too. So there's something about you that is probably more adapted to that environment, which is to your advantage.

[00:05:41] Sam: possibly Yeah, I definitely melted a little bit when I did it in 2022 so i'd like to go back and Write some wrongs. That's let's put it that way.

[00:05:50] Taryn: Think about all the things you know now, though, that you could apply to yourself. You know, n equals one, you're always your own experiment. You would know so much more about that sort of stuff to help you for future racing.

[00:06:02] Sam: Yeah, exactly With ironman racing. I really like it, but it's you can't do that many a year Maybe one or two that you can peak for and You There's a little bit of jeopardy involved in that as well because, you know, we pay a lot of money to enter these races. it could all go terribly wrong but you could also have the perfect day. And I think that's what I always think is one day will be possible to have the perfect day at one of these races, not yet. But yeah, it will happen at some point.

[00:06:26] Taryn: Yep. And then it'll never happen again. Just happens once. We're going to get pretty deep on carbohydrate and fat oxidation, particularly for triathlon. We did have Professor Louise Burke come and talk to us about low carb, high fat and fat adaption stuff way back in episode 79, if you do want to go and listen to that.

[00:06:49] Taryn: that was back in February 2023. So I haven't really covered the fat oxidation, carbohydrate oxidation stuff too much since then. But we have so much to cover that what I'm going to do is break this episode into two parts. So part one, we're going to focus mostly on carbohydrate oxidation. And then I'm going to get Sam back on.

[00:07:10] Taryn: And we're going to talk about fat oxidation in part two. So hang on in there. I promise we're going to get super practical and not get too deep in all of the finer details of stuff so that you will be able to keep up and understand. Sam is really good at explaining the science in practical terms as well.

[00:07:27] Taryn: So to kick us off, Sam, can you kind of explain the basics of carbohydrate and fat oxidation and how that contributes to our energy production in particular in endurance sports and things like triathlon?

[00:07:42] Sam: Yeah, so 

[00:07:42] Sam: the basic principle is that the longer, you know, we go as an endurance event, when we're doing prolonged exercise, then the more that fat is going to contribute to our total energy expenditure.

[00:07:54] Sam: we can look back at, there's a couple of, like, really nice key studies that showed this back in the early 2000s. So, Matt Watt, , who's based in Australia he did a study where they got people to cycle for like 4 hours, just at a moderate intensity. and in this study, the crossover point was about two hours, where after two hours, fat became the dominant source of energy, whereas carbohydrate oxidation became lower after two hours.

[00:08:18] Sam: Before that point, carbohydrate was the dominant source. So, that really showed idea of a crossover and how prolonged exercise influences the proportion of energy that we're generating from fat and carbohydrate sources. And then there was a study a year later that came out from Luke Van Loon, another like really prominent researcher.

[00:08:37] Sam: It's probably one of the most cited papers I think ever in exercise metabolism his paper in 2003. in this study from Luke Van Loon, they just did two hours of exercise, but they used stable isotopes and this allowed them to identify the sources of carbohydrate and fats that were being used during moderate intensity bout of exercise.

[00:08:59] Sam: so early on during that endurance exercise, then typically you use substrates that are available in your muscle. So primarily muscle glycogen, but then there's also some fat stored in there as we kind of touched upon as well. And then as that exercise then continues and we go longer and deeper into that exercise bout, then you start to see a shift towards more use of plasma based sources.

[00:09:25] Sam: And what we really mean by that is that over time, then we will be releasing more fatty acids from our adipose tissue stores. So our fat stores and that's traveling to the muscle. And I have been taken up and oxidized. We also see a greater proportion of energy coming from our glucose in the blood. And what we really mean by that is the glucose that's being produced.

[00:09:47] Sam: broken down from liver glycogen stores and pumped out, and again, taken up and being used to generate energy. So that's the real basics, I suppose, and those are the two, like, key studies I always go back to, to kind of reflect on how does an endurance exercise bout, influence substrate, or the substrates that we're using.

[00:10:09] Sam: Now in both of those scenarios, in both of those studies, they're very controlled, and obviously, During an event, and the likelihood is we're going to take on carbohydrate during that event. And so that's going to maybe influence where that crossover point actually sits. So, you know, if we take on more carbohydrate early on, then it might be that we remain more carbohydrate dependent.

[00:10:30] Sam: And carbohydrate provides a greater proportion of energy for longer into that endurance event. But that's the kind of basics in a nutshell, really.

[00:10:38] Taryn: Yeah, nice one. Thank you. Does the intensity of exercise then affect our substrate usage?

[00:10:45] Sam: absolutely. So, and Again, there's another really great study from Luke Van Loon, which looks at, again, using the stable isotope look at the sources of carbohydrate and fat that have been burned at different exercise intensities.

[00:10:59] Sam: This was actually published a couple of years earlier. So 2001, again, probably one of the most cited papers in that, in that area. And they showed that, yeah, around 50, 50 percent of your energy is coming from fat oxidation at, you know, a moderate exercise intensity. The higher intensity that we go, then there's a greater proportion of energy coming primarily from muscle glycogen stores.

[00:11:20] Sam: So, the harder we work, the more muscle glycogen we're going to burn to generate that energy, of course. those are two very controlled studies. Thanks. But again, if we apply that to what a race might look like, and most of the courses that we will ride on the bike in particular, and maybe run.

[00:11:37] Sam: There's going to be some ups and downs, so it's either going to be undulating, or there's going to be some severe hills, so the intensity will change naturally throughout that as well as obviously it being a prolonged exercise part, so it's not as, you know, not as quite clear cut as the lab studies would make you believe, yeah.

[00:11:52] Taryn: we're not particularly stable even in training, you know, you might do efforts in a session or you go up a hill and the intensity suddenly shifts and your oxidation of carbohydrate and fat suddenly shifts. So how can somebody know at an individual level what their carbohydrate and fat oxidation rates are at different intensities?

[00:12:13] Sam: Yeah, so part of like a physiological profiling of an athlete, right? Is do a graded exercise test. So we often split that into two parts. So like, a submaximal part of that test. And that's where we'd really start to determine what we might call fat max.

[00:12:28] Sam: So the intensity or the workload at which someone is burning that, or their maximum fat oxidation sits up. And that's typically sort of somewhere in the region of 45 to maybe 65 percent of VO2 max. Thanks. And then we can continue that track change or the reduction in fat oxidation as exercise intensity goes up.

[00:12:50] Sam: So, again, if you take, if we did a simple test on the bike you know, we might start off someone cycling at 90 or 100 watts, and then it would go up 30 watts every 4 or 5 minutes. And we can see how that changes substrate utilization, those increasing intensities. So naturally what we'll see with fat oxidation is it generally goes up a little bit and then will come down.

[00:13:12] Sam: Carbohydrate oxidation will continue to rise. So, really, the only way to truly know how much you are burning of both of those substrates is to go to a lab and have that tested using a metabolic cart where we're collecting that expired air, collecting information on the volume of oxygen that's being consumed, the volume of CO2 that's being produced, and then those two values go into equations to determine your rates of carbohydrate and fat oxidation. we can also use that technique coupled with a stable isotope to determine exogenous carbohydrate oxidation rates as well. to. So yeah, exogenous carbohydrates are carbohydrates that are ingested essentially. So that's really important if we want to understand the rate at which we use the carbohydrates that we ingest, then we would add a little bit of a tracer to those. So a tracer is basically a very similar well, very similar, it acts the same in terms of the molecule. That's exactly the same, but it's tagged slightly differently slightly heavier.

[00:14:19] Sam: And then we can, we can analyze that using sophisticated methods after the test. But what it ultimately tells us is of oxidation of the ingested carbohydrates. So if we take 30 grams of carbohydrates in a gel, what rate are we burning that at? And that will alter depending on XR's intensity as well but it still requires us to collect the expired air that we're breathing out, understand the volume of oxygen that we're consuming and plugging it into similar equations to be able to do that.

[00:14:49] Sam: Okay. So that takes techniques really good. I would say the first thing I talked about there, the graded exercise test that's relatively inexpensive for someone to go and do at a laboratory. Typically in the u uk we can do that at universities. Most universities offer that type of service.

[00:15:04] Sam: The exogenous carbohydrate oxidation rate is very expensive because the stabilize isotope tracers. Are expensive to buy and then analyze as well because of the mass spectrometry that we use to do those analyses. If you have the budget of someone like a Christian Blumenfeld or Gustav Iden, you'll see those guys probably on YouTube doing that.

[00:15:25] Sam: Relatively often to understand what their exogenous carbohydrate oxidation rates are for us mere mortals, unfortunately we're not going to be able to do that unless you have a lot of money to be able to invest in that. So, yeah, that's not ideal. there are apps, I suppose, and they're becoming more prominent now. That's at least claim to be able to work out how much carbohydrate you've burned during a session or how much fat you've burned during a session. they'll give you a ballpark figure, but I also, they're not built to take into account, you know, changes in temperature altitude. what your food intake was before and during that session your fitness level.

[00:16:03] Sam: These are all. Different factors that are going to influence the contribution of fat and carbohydrate to your energy expenditure during a specific session. So, they'll get you in the right region, but they're not particularly informative in my opinion at this point in time.

[00:16:17] Taryn: So if somebody gets that data, I don't know, they end up in a research study or something or they pay to have that commercially done.

[00:16:24] Taryn: they have their carbohydrate oxidation rates, they have their fat oxidation rates at different intensities. Are there factors that are going to affect that or change that? Or is that their number forevermore, set and forget?

[00:16:37] Sam: No, can definitely be changed. The main thing that will change it is their sort of training status or fitness level. So as we get fitter, then at the same intensity, we should be able to use more of our fat stores to generate energy versus our carbohydrate stores. you know, if my fat max, for example, was something like 0.

[00:17:00] Sam: 5 grams per minute, which is average for your recreationally active to well trained individual, for most people at least anyway, following a sort of normal, you know, 65 percent carbohydrate diet. If I then did a period of, endurance training, 12 weeks, 16 weeks, something like that, and came back and then retested.

[00:17:22] Sam: I would hope that one of the outcomes from that would be that my maximal fat oxidation would've increased maybe up to like 0.6 or 0.7 grams per minute, either at the same tower. So if it, occurred 150 watts for argument's sake in the first test, and then the second test, it also occurred 150 watts, that would be okay.

[00:17:43] Sam: Or the ideal scenario is we'd actually be using more fat at a slightly higher power this time. So maybe like 180 or 200 watts. So that means that we're generating energy a little bit more efficiently and protecting our Carbohydrate stores essentially and for the same sort of level of effort. Let's say

[00:18:02] Taryn: I find that so interesting. And what I want So what I want you to take away from that is that if you are less fit or you're coming back from, I don't know, Christmas and New Year period and not doing a lot of training, or you've been sick or injured and not done a lot of training, or you're new to the sport, then your carbohydrate needs are higher than somebody that is fitter and faster and well trained.

[00:18:25] Sam: the other point I should make here, but some people often take away from this is that Okay, so I go to a lab I get this test and it tells me my fat max is 0. 5 grams per minute and then They extrapolate that out into a, you know, four or five hour ride, that's all they're ever going to burn, 0.

[00:18:44] Sam: 5 grams per minute. But actually remember, you know, right at the start, we talked about how exercise duration, so the longer we go, the more that will, that will contribute to our energy needs during a sort of endurance type exercise bout. So, yeah, it might be that. You know, you start off at like 5 grams per minute.

[00:19:04] Sam: The longer you get into that exercise bout, it's going to go slightly higher. So, you know, maybe after two or three hours, you'd go in at sort of one gram per minute. So the thing to take away is that you can't go to the lab and say, okay, 150 Watts, I'm going to burn 0. 5 grams per minute of fat and 1. 5 grams per minute of carbs.

[00:19:22] Sam: you know, people take that wing and think that can influence their race strategy because they know how many carbs they're burning. It doesn't quite work like that because of the fact, you know, factors or the main factor being the exercise duration will influence that relationship and that will shift over time.

[00:19:38] Taryn: So we all just need massive budgets and all the money in the world to sit in a lab and do as much testing as someone like Blumenfeld or, you know, the Tour de France riders. They are pretty heavily dialled in, right? They have so much money and science backing to get all that stuff right. I think it's very, very cool and very interesting.

[00:19:59] Taryn: So fitness is the main driver of those things. 

[00:20:01] Sam: Yeah. Fitness is one of the main drivers of those things. There are some small differences when we look at things like sex. So we know that females at the same sort of relative exercise intensity use a little bit more fat than males do. If you go to altitude, so I can speak a little bit about that because luckily I was at Font Rameau in the Pyrenees a couple of weeks ago with some Hoka runners and it was good to see that they were aware that their carbohydrate requirements were going to be higher. At altitude, because you're working, you know, relatively harder, so the intensity of the exercise is generally higher. Therefore, you're going to use more carbohydrate. So they need to fuel a bit higher during those sessions to try and overcome. And compensate for that, you know, temperature, obviously, is going to influence that as well.

[00:20:48] Sam: So we've just seen Kona the last weekend just gone, you know, people are going to be using more carbohydrate and heat unless they dial back the intensity that they're riding at, which we obviously didn't see with some of the guys hence why they were walking on the run and various things.

[00:21:02] Sam: So those are the kind of main, yeah, some of the main things that are going to influence it. And And we'll probably talk about this a little bit as well. Probably the key factor is our habitual diet as well as kind of training status you know, whether we have a high carb diet or a lower carb high fat diet is going to play a big role in what the substrate is that we use during exercise.

[00:21:23] Taryn: Yeah, I will ask you that question, but before we dive into that I want to get your take on the 120 grams of carbs an hour, you know, trend, if you want to call it a trend that we're seeing everywhere because there's some literature around, you know, elite level off road marathon runners, like trail runners chewing through that much carbohydrate and everything always trickles down to age group athletes.

[00:21:51] Taryn: And it seems like. The focus for people at the moment is like, more is better. Let's all aim for 120 grams of carbohydrate an hour. Why would somebody that is an age group triathlete want to aim that high? And I guess on the flip side, why would you then not want to do that in other situations? 

[00:22:09] Sam: So first of all, we should say that we think that the maximum absorption capacity of the gut to take up glucose is about 1 to 1. 1 gram per minute.

[00:22:20] Sam: So that's where this idea, if you had only glucose, you could ingest and absorb and oxidise about 60 grams per hour. And then we knew, you know, back in the early 2000s that If you added fructose to glucose, then we could increase that optin 90 grams per hour. It's worth, thinking about those studies, actually, because in those first studies, they actually fed their participants about 108, 110 grams of carbs per hour.

[00:22:52] Sam: And that was, again, a combination of glucose and fructose. And when they did that, they observed oxidation rates of 1. 5 grams per minute. So 1. 5 times 60 gives you 90 grams per hour. So that's where that 90 grams an hour has come from. And in recent years, we thought, oh, can we push that a little bit higher?

[00:23:13] Sam: So those initial studies had a ratio of two to one glucose to fructose. So 60 grams of glucose, 30 grams of fructose, for example. More recent studies have looked at using a slightly different ratio. So 1 to 0. 8 for glucose to fructose and that's meant that we can push it slightly higher And that's the basis of those studies that are showing that maybe 120 grams an hour is possible it's also worth saying that the maximum or at least on average the maximum oxidation rates that they observe in those studies Is still about 1.

[00:23:48] Sam: 5 grams per minute. So there's maybe a little bit of redundancy You could say in, in doing that, you could actually bring it back down and this is worth considering from an age group perspective. If you want to maximize your carbohydrate oxidation rates, you could probably actually aim for somewhere in the region of 100 to 110 grams per hour. And you would still be pretty close theoretically to those maximum oxidation rates. And obviously you're reducing a little bit of potential gut issues by putting something in that isn't getting absorbed and oxidized. You know, and that, that might not seem like a lot, we're talking about 10 grams there maybe, but if you extrapolate that out over five or six hours of an Ironman bike, then you're potentially carrying 50 to 60 grams extra carbs in the gut that aren't actually being used.

[00:24:36] Sam: And yes, there's going to be some carry through into the run there, of course, but there's also potential for GI issues that come alongside that. So there's a, good training element of that as well. I think. And it's interesting that you noted the, the ultra running study that actually fed 120 grams an hour, because that was probably one of the first ones to show that.

[00:24:57] Sam: And it's interesting that it was in runners. Now, anecdotally, and, um, with the cyclists that we work with at Precision, we see regularly they're doing 120, even 130, 140 grams an hour. And I think in cycling, it's a little bit easier to meet those numbers and hit those numbers. There's also a reason to try and do that, particularly, you know, when they're racing like multi day or multi stage races, there's an element of if you feel higher today, you're not digging such energy hole, let's say, that you can't then recover for the next day.

[00:25:30] Sam: And so that's part of the reason to go pretty high on those on those days as well. Interestingly, though, and it's probably. At western states marathon this year when I was first exposed to this and saw this that if you Take ultra runners, even those guys, you know, they're running for 10 12 15 hours Even those guys are hitting around 100 grams an hour, which Is incredible.

[00:25:55] Sam: And also we should say that that's largely from sports nutrition products like gels or chews, which to me seems unfathomable. And particularly, my assumption was always that there would be some real food in there to mix things up, but they're just, no probably the best example of that is Hayden Hawks, who won at UTMB this year.

[00:26:16] Sam: And he was third this year at Western States. He was, yeah, about 100 grams an hour purely from gels over, you know, a 10 to 14 hour period, which is just immense. You know, we're talking there at the top level, of course, and those guys are really pushing the limits. And we'll probably repeat this point.

[00:26:33] Sam: It ultimately comes back to what intensity do you think you're going to try to complete an event at and that will, to some extent, determine how much carbohydrate you try to consume. So, if you're aiming to complete an Ironman in 15 hours, the relative intensity is going to be much lower than one of the pros trying to do sub 8, for example.

[00:26:55] Sam: They're going to be working at a much higher intensity to do that, so there's a reason to have such high carbohydrate intakes for those guys. guys. If you're, you know, if the intensity of that exercise and that race is going to be much lower for you, then you could probably dial that back and you will naturally use more of your fat stores to generate the energy to be able to keep you going essentially during that, during that race.

[00:27:18] Sam: I'm not saying that fueling isn't important. Of course, it's still important, but you could dial that back maybe to 60 or 70 grams an hour if you're if the intensity of that, if that race is going to be a little bit lower as well. So I think it. It all comes back to considering this on an individual basis, and yes, there's some level of what can you tolerate, because that's a big part of it.

[00:27:38] Sam: But also what do you think you're actually going to need as well, based on your target and aims for, for the race.

[00:27:45] Taryn: So you alluded to this before, but what part of You know, somebody's day to day nutrition is going to dictate how good they are at oxidizing carbohydrate or oxidizing fat.

[00:27:57] Sam: there was actually quite a nice modeling study done of this a few years ago from Dan Plews and Jeff, Jeff Rothschild over at AUT. Thanks for having me. And they took up heaps of data basically and looked at what factors would influence RER. So RER and we can use that as a an indicator of how much carbohydrate we're using or how much fat we're using, or at least the proportion of either.

[00:28:24] Sam: Either or. So, an RER of one in theory would tell us that we're burning a hundred percent carbohydrate. An RER of 0. 7. Would tell us that we're burning entirely fat. And so, you know, 0. 85 would say 50 50, basically, and you get that from the, going back to the lab tests, you would get that information from those tests, because it's a, just a a ratio of VO2 to VCO2, essentially. So, yeah, when they, took all that data, and. Looked at what factors would influence RER. Yeah, exercise duration was a key one. The other key one was habitual diet. So if you have a higher fat diet, then naturally you will burn more fat during exercise and equally if you have a higher carbohydrate diet, there will be a tendency to use carbohydrate and obviously we can change that based on our habitual diet. So we suddenly decide that we want to play with low carbohydrate high fat diets. For example, then we might start to see a shift to using more fat as a fuel and equally if we maintain a, most people have a fairly high carbohydrate diet then carbohydrate is going to be one of the more dominant sources.

[00:29:36] Sam: that's the main thing really. there is some evidence that gut health is going to be important in that as well. So, it's not just how much fat you have, or how much carbohydrate you have, it's also the quality of our diet, of course. We need to look after our gut microbiome, so if we've got poor gut health, that's going to definitely have an influence on how well we, you know, absorb and then use either fat or carbohydrate, essentially.

[00:29:56] Sam: So, you know, it's important that we're getting sufficient things like fiber in our diet, for example, to to support good gut health. But it's the proportion of carbohydrate and fat which is going to be a big determinant of how much of that we then use during exercise

[00:30:09] Taryn: I've been trying to keep an eye on that gut health space because, oh, I just find that I'm always banging on to athletes about eating more fruits and vegetables, but there is method to the madness. Particularly for you guys in the UK, your, your diet is shithouse, no offence. You guys do not eat enough fruits and vegetables, you really need to pick up your game for the rest of the world.

[00:30:31] Sam: Wow, okay. I mean i'm just looking at a fruit bowl now on our work surface So, um, you know, I can't comment for the rest of the uk. We're doing all right here at precision

[00:30:41] Taryn: so to take you back to carbohydrate and fat oxidation, we can change that like relatively quickly and I know Louise Burke has done a lot of stuff in, you know, low carb, high fat and, and flipping somebody's oxidation rates with diet.

[00:30:56] Taryn: I don't know how to ask this question properly because I know so many age group triathletes, you know, want to dabble in the low carb, high fat thing. They, they talk about, you know, being fat adapted and improving that.

[00:31:09] Taryn: Is that something that they should be looking at doing to get better at burning fat, particularly more long course athletes? Or is it a bit of a waste of time and a gimmick?

[00:31:18] Sam: Ah the million dollar question. The first thing that I would say to someone who came to me asked that question, would look at across, you know, what does their actual life look like?

[00:31:29] Sam: So if they have a family and their cooking is the family, or is the family prepared to, you know, adopt that same low carb, high fat diet. Do they do a lot of preparation of their meals or do they try and, you know, are they grabbing food on the fly when they're, you know, in and out of the office, for example, because it seems to me that we're in a quite a carbohydrate heavy environment.

[00:31:52] Sam: So if you're trying to pick up lunch, you're going to have very limited options to sustain a low carbohydrate, high fat diet. And. ideally a low carb, high fat diet should have less than 50 grams of carbs per day. That's incredibly difficult unless you are well planned and well prepped for every day.

[00:32:12] Sam: To be able to sustain that, if you can do that, then hats off to you for that to start with. But if you can do that, then I think there's probably is some benefit to, let's say, dabbling with it and seeing if it fits for you. We know that that strategy is going to increase your ability to use fat as a fuel So more of your energy is going to be generated from your fat stores as a result of doing that That's quite unequivocal and as you alluded to Louise has shown that that can happen quite quickly as well the other Aspect of that is that when you adopt that dietary strategy You're often compromising your abilities to do like the high intensity work. Now that might be fine to some extent, but we know that, you know, fitness and VO2 max. And if you're trying to do VO2 max type sessions or workable threshold to improve your VO2 max, that requires a lot of carbohydrate to actually achieve that. And we know that VO2 max is, you know, probably one of the key determinants of performance, whatever level of an athlete you are. There's probably so there's no right straightforward answer for that, unfortunately, and I'm sort of skirting around saying yes or no, because I don't think you can. There's a bit of a gray area. I think it's very individual. And I think it goes back to what your aims are as an athlete. And, you know, if you're aiming to compete at the high, at the top end and go, you know, sub 8, sub 9 in an Ironman, for example.

[00:33:44] Sam: then I think you're probably going to need a heavy component of your diet to consist of carbohydrate. Because you're not, you're not typically going to be able to do the high end work that's required to go that fast. If you're at the lower end, and again, we can, we can look at this from, yes, an athletic perspective, but also from a health perspective, then maybe low carb, high fat approach is potentially a good strategy.

[00:34:10] Sam: We know it's not a bad thing for health particularly, you know, when we in my former life as an academic, when we were doing some, you know, looking at overweight or 2 diabetics, there's pretty good evidence that a low carb, high fat diet can help with that insulin sensitivity or, or reducing that insulin resistance.

[00:34:29] Sam: So it could be an option. I also think, have a, an athletic life, let's say, or maybe we stopped competing and then. you know, if we have a high carbohydrate diet, maybe that's not optimal for what we, you know, if we then create a sedentary state for ourselves.

[00:34:46] Sam: Ideally, we don't do that, of course, and we keep moving. But we might not be competing or completing events. So, yeah, I'm sort of going all around the houses here to say that it's a pretty gray area. I think if you can commit to it, and that's the other thing to say, if you can commit to a low carb, high fat lifestyle, I'll call it not even a diet, a lifestyle.

[00:35:07] Sam: And I think there's some potential benefits depending on your ambitions, your level as an athlete and what you're trying to achieve.

[00:35:16] Taryn: Yeah, perfect politician, right? No, no straight answer. I love that you led with the lifestyle thing first though, and I love that also a dietitian on the other side of the world has the same mindset around this with athletes. I've only ever met two athletes in my entire career that have maintained and benefited from a low carb, high fat lifestyle.

[00:35:40] Taryn: Everyone else has wanted to do it because it's sexy, but cannot maintain it for longer than a couple of weeks to, you know, a couple of months. And they uproot their entire life and their family, and they discover how hard it is to eat out, and they can't do any social things, and they can't go drinking with their mates and things like that, and they're like, screw it, it's too hard, it's not worth it.

[00:36:00] Taryn: So I think it's definitely something to consider first and foremost before you start. chasing shiny objects and jumping down rabbit holes to get a marginal performance gain if it's going to affect your entire life.

[00:36:14] Sam: Absolutely. I mean, I suppose I'm saying that based on some experience as well. I actually dabbled myself a few years ago 

[00:36:22] Sam: yeah, it wasn't an enjoyable three months if I'm being perfectly honest. It just didn't fit for me as an athlete. 

[00:36:28] Taryn: did you notice any performance gains off the back of that then?

[00:36:32] Sam: it's difficult to say. So I actually had a 10k race a week into it and I ran pretty fast, but equally, that's the first time I wore a pair of super shoes as well. So you know, we can't put it all 

[00:36:42] Taryn: Oh yeah, scrap, scrap 

[00:36:44] Taryn: that. Nope. Too many

[00:36:46] Taryn: confounding variables to your research study there. That's 

[00:36:50] Sam: Yeah. Yeah. No, but the main thing for me was that it just didn't fit with. The life that I was leading, I suppose, at the time and my lifestyle generally fairly good at preparing, you know, food and things like that. But as soon as you have a few busy days and you fall behind on that, you just, you're almost scrabbling, uh, you know, a bit like you do with work sometimes.

[00:37:11] Sam: you're out of the LCHF sort of lifestyle, let's say. And it's difficult to get back to it.

[00:37:17] Taryn: would love to keep talking, Sam. So what I might do is we're going to wrap up part one. of the carbohydrate oxidation information. So many good little tidbits and, and practical applications there. I love as a researcher being able to talk to you that you can just pull research studies out of your brain and be like, they did this and they did this.

[00:37:37] Taryn: I don't ever retain that stuff. I read it. I'm like, Oh, that's cool. Now, how do I apply it? and what is then my advice to somebody and then I lose all the detail from those papers and I love somebody that can just pull that, pluck that out of their brain. So let's wrap up part one. Thank you for listening to All About Carbohydrate Oxidation.

[00:37:56] Taryn: I'm going to come back with with part two with Sam and we're going to keep diving down this low carb, high fat, fat oxidation and fat adaptation type strategies when it comes to endurance performance. So thank you so much, Sam. And I will talk to you soon. 

[00:38:12] Sam: thanks. Thanks for having me and speak to you soon.

 

Thanks for joining me for this episode of the Triathlon Nutrition Academy podcast. I would love to hear from you. If you have any questions or want to share with me what you've learned, email me at [email protected]. You can also spread the word by leaving me a review and taking a screenshot of you listening to the show. Don't forget to tag me on social media, @dietitian.approved, so I can give you a shout out, too. If you want to learn more about what we do, head to dietitianapproved.com. And if you want to learn more about the Triathlon Nutrition Academy program, head to dietitianapproved.com/academy. Thanks for joining me and I look forward to helping you smashed in the fourth leg - nutrition!