Episode 118 - Continuous Glucose Monitoring for Triathletes with Greg Cox

Continuous Glucose Monitoring for Triathletes with Greg Cox

A hot topic in the endurance space at the moment and one I know you’re extremely interested in - Continuous Glucose Monitors (CGM) and their use in sport. 

To help me dive into what we know so far and if they’re worth investing in is fellow Sports Dietitian Greg Cox aka Coxy. Co-author of newly published review paper: The Use of Continuous Glucose Monitors in Sport. We dive into:

  • Why are we so interested in CGM in sport?
  • How do CGMs work?
  • What’s the difference between sports specific CGMs vs those available for diabetics?
  • How to interpret the results and apply them in practice
  • Factors that affect your fuel use and CGM data
  • Coxy’s thoughts on using starches for fuelling
  • Future research and directions for CGM

If you have one or have been thinking about buying one, listen to this episode first!

⚡Learn More About the Triathlon Nutrition Academy⚡



Bowler AM, Whitfield J, Marshall L, Coffey VG, Burke LM, Cox GR. The Use of Continuous Glucose Monitors in Sport: Possible Applications and Considerations. Int J Sport Nutr Exerc Metab. 2023 ;33(2):121-132. doi: 10.1123/ijsnem.2022-0139.

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Episode Transcription

Episode 118: Continuous Glucose Monitoring for Triathletes with Greg Cox

Taryn Richardson  00:00

Today's episode is with the one, the only Mr. Gregory Cox. Now unless you're a sports dietitian, you probably haven't heard that name before, but Coxy is an absolute legend. I have so much respect for this man. I've known Coxy my entire dietetic career. He was the man that took the sports nutrition course that I did to become qualified as a sports dietitian back in, I think 2009. And I had the honour of working with Coxy at the Australian Institute of Sport for my fellowship. And then that, went on to become my contract through Triathlon Australia. He basically taught me everything that I know and has been pivotal to my entire sports dietitian career.  He currently holds a teaching position at Bond University on the Gold Coast here in Sunny Queensland and is actually an incredible triathlete in his own right. He is a weapon on the racecourse, but now mostly dominates the surf Ironman scene and does a tiny amount of training to claim the title every year. He should have been on the podcast way earlier than he is but the reason that I've asked him to chat with me today is because he's recently published a paper on the use of continuous glucose monitors in sport, which is a topic I know that you are extremely interested in. A lot of their Triathlon Nutrition Academy athletes talk about it and I think it's great to get his perspective on it. So, without further adieu, let me introduce you to the legend that is Greg Cox. 

Taryn Richardson 01:38

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.

Taryn Richardson 2:15

Welcome to the podcast Coxy! Bringing the A-Team back together. 

Greg Cox  02:19

Hey, thanks for having me. 

Taryn Richardson  02:21

I was just saying offline, this is probably a little bit weird, you're like my ultimate, like mentor. You've shaped my entire sports nutrition career and I'm talking to you on my podcast. The tables have shifted, is it weird Coxy? 

Greg Cox  02:34

It is weird I'm a guest. I feel privileged to be a guest. I've been waiting for this call forever. I thought it was never coming. 

Taryn Richardson  02:41

Ah, you are welcome anytime. I'm happy, like maybe you could be a co-host on the Triathlon Nutrition Academy podcast. There is no one better qualified to be my co-host. What do you reckon? 

Greg Cox  02:53

That'd be great. I have to get a new shirt. I like orange so I could get something blue perhaps, that's my two favourite colours. Yeah.

Taryn Richardson  03:00

Yeah, that's the brand colours for the podcast so we're in sync. 

Greg Cox  03:04

Man. Unreal.

Taryn Richardson  03:07

So I've invited you on eventually. I'm happy to chat to you anytime about all the things. You are like the first person I think about when I have a challenge when it comes to nutrition. But today, I want to pick your brain on continuous glucose monitors and where we're at in understanding their use in sport. I've actually been putting off this episode myself, for ages because it's big, like it's deep. There's lots of things we need to consider. And so to have you on to do like we used to do back in the day of the A Team, pick your brain is an honour. 

Greg Cox  03:41

Well, I certainly appreciate you having me on. And CGM's something that we've been chasing the last couple of years so I think it's very topical, probably most topical in endurance sports so it has a lot of application in triathlon. 

Taryn Richardson  03:56

Yeah, so all of the listeners are triathletes. We have a few random you know, swimmers that wish they did triathlon and cyclists and things like that, but definitely endurance focus. You have co-authored a new paper on the use of Continuous Glucose Monitors in sports. We're going to call it CGM for short because it's a mouthful. Published in 2023 but it's something that you have been working on for the last sort of three or four years. And I'll link that paper in the show notes if you do want to dive into it.  But I wanted to get your thoughts on like the lay of the land with where it's at now because you're really across the limited the five studies research that is in this space. But to kick us off, why are we suddenly obsessed with these things? Like why is it just exploded in the sports space? 

Greg Cox  04:40

CGMs have been around in diabetes management for say 20 plus years. And they're able to, in real-time, monitor the response to exercise and also diet, so what they're eating from one meal to the next. I guess it was only recently conceived that they might have applications outside of people with diabetes. I can't recall the specific date, the first option came out for people that didn't have diabetes but it's probably been the last three years. So I think it's the why are we interested because they're reasonably non-invasive and you're getting a metric. And everyone these days, they love a metric, right? 

Taryn Richardson  05:22

Triathletes in particular, love it, love the data. 

Greg Cox  05:25

And it's, I guess it's an output data from the interaction between exercise, rest, and diet. And so rather than asking someone about their dietary intake, and no one loves doing that, because it's time intensive, it requires input from the consumer. And so you can put a CGM on and that gives you an output from that. So I often look at, you know, an athlete, their machine. And so there's some inputs into that machine and then you can measure some outputs right. So you can measure dietary intake that goes into the machine, or the athlete, but that's cumbersome, or then you can measure the outputs. And that might be performance, might be CGM response, or their blood glucose response. And CGM isn't quite blood glucose but it mimics your blood glucose. 

Taryn Richardson  06:17

So for somebody that's never used one before or know how they work, do you want to explain that? Like, explain how you actually put one on and what it's measuring? 

Greg Cox  06:26

Sure. So with CGMs, continuous glucose monitors, they measure the glucose concentration in your interstitial fluid. So you fluid in your body and surprise to many, you're probably made up of somewhere between 55 to 65% water, right? The leaner you are, the higher the percentage, essentially. And that's because water is much higher concentration in lean mass compared to fat mass. So I'd say 55% to 60%, your body's made of water. A certain amount of that water lives within the cell, and then a certain amount of water lives extracellular so outside of the cell.

Taryn Richardson  07:07

Love a good science lesson. 

Greg Cox  07:08

Yeah. And so it's about two thirds within the cell and about a third outside of the cell. Outside of the cell, you have the plasma, everyone's familiar with plasma within your blood. And then you've got an interstitial fluid and so that sits outside the cell around the cells. And so if you want to measure plasma glucose, you can either take a blood draw to do that and that's not particularly, it's reasonably invasive. People will be familiar with that when they go to a pathology lab and they get their blood screens. And you would get perhaps a fasting blood glucose so you might even get a random blood glucose. You can take capillary glucose which is more commonly used, again with people that are living with diabetes. And that's where they might prick their finger to give an idea of their capillary glucose. And capillary and plasma glucose, they relate really closely.  Interstitial glucose is essentially the glucose that sits like in that extracellular fluid that's not plasma. And it runs a delay of about 10 to 15 minutes behind plasma glucose. So whatever happens in the plasma, the interstitial glucose sort of follows that. The two events are known to be reasonably reflective of each other. With a CGM, they are devices that are typically put in the upper arm, at the back of the arm, or in the lower part of the abdomen, and a small insertion and it's probably like a bristle of a toothbrush, but a little bit shorter than that. So the monitor has a very small like, sort of like a nylon thread that goes into the interstitial sort of well, just below the skin interstitial space. And that monitor picks up the glucose that sits within the interstitial fluid.  And so from that, that sort of links back to a, like an iPhone app. And so some of the CGM monitors, you have to swipe past the monitor every eight hours and it will download the data, or some of the new CGMs they will talk wirelessly to a phone, and even some of the other devices that you would track your metrics on as well. And so in real time, with a, let's say, a delay of 10 to 15 minutes, you can see, well, essentially your blood glucose response or your interstitial glucose response. 

Taryn Richardson  09:24

Yeah, it's pretty cool. Like I can definitely see why people are really interested in it. And there's lots of devices being developed in the sport specific market now. Like, it's been around for forever with diabetes. Is there any difference between those diabetes monitors and the sport specific one that's on the market? 

Greg Cox  09:42

Yeah. So with this sport specific monitors, typically, what they do is that they limit the range of capture that the glucose will report on so it can't be used as a diagnostic sort of tool. With a regular monitor that you might purchase if you have diabetes or living with diabetes, it would measure your blood glucose down to very low levels, right up to extremely high levels. And the variation that someone that's living with diabetes would have, they might have a blood glucose or like a low blood glucose or of like 2 or 3 millimole, right up to the mid to high 20s, right? So normal range is between 4 and 8. It's normally lowest in the morning after that overnight fasting period. And then it might peak like quickly after a meal and then come back within that sort of that range of 4 to 8.  So most people that have a healthy glucose response would spend almost 100% of their time within that range. They might spend a small amount of time 1%, perhaps outside of that range. People that are living with diabetes that have poorly controlled diabetes, they spend much more time outside of that range so they have larger swings within their blood glucose, or the neck glucose. And that's been shown how to various health consequences, so the long term consequences. 

Taryn Richardson  11:02

Interestingly, this sports specific one is like double the price of a normal diabetes one and it's not TGA approved. Is there accurate data coming from those sensors yet or do we just not know their accuracy? 

Greg Cox  11:19

No, the device itself is the same device that's used, they just spec it differently. So the accuracy is where you wouldn't expect it to be any different. The range of which it captures is a lot smaller than the range that you will have with other monitors. So there's a range of different ones now. There's Levels, which is a brand out there, the Supersapiens, which is perhaps the most commonly known brand out there as well. And they have used, they typically have used monitors that are existing monitors but they get them spec differently, and then they're able to sell them for...  Well, it's not about that. Like, interestingly, the monitors that have now sold people that have diabetes in Australia, they've just been subsidized for people with diabetes and that's because like they have great outcomes in terms of their longer term health. So you can purchase a device, for instance, that is available for people with diabetes on the internet if you chose to do that. And depending on which device that you went to buy, the cost do vary. And it's based around some of the consumables that you need for the different devices. 

Taryn Richardson  11:54

More money.  So we're plugging the data into an app or some sort of program. I see the challenge with a layperson interpreting that. How does somebody you know, plug and play that and go, how do I make meaningful assumptions or change what I'm doing based on the data that's providing me? 

Greg Cox  12:40

Within the diabetes sphere, there's a few metrics that you would then produce with the data, typically, the theme of those metrics is around capturing variability. And so that's variability throughout the day, there's also metrics from day to day as well that you might look at. And some of the platforms that have been designed for people with diabetes, the size of the grass are developed for people that are going to have much larger swings in their blood glucose and you would expect for somebody otherwise healthy. So even looking at the graph, you can't really see too much because the graphs built like this, and there are fluctuations that someone's health is much smaller. So you're really looking at variability within your response during exercise, perhaps and also, you know, during rest periods throughout the day.  One of the areas that we've become interested in is what happens overnight. So when you remove the interaction of exercise and diet from the equation, like what's happening to your blood glucose from that sort of overnight period, so 10, let's say, to 6 in the morning, and depending on how you want to cut it out, it might be slightly shorter than that. And that might tell you something about your overall fuelling for instance, like from day to day, as opposed to your acute fueling in response to a particular exercise session. There has been a handful of case studies that have reported CGM data from athletes particularly in ultra endurance events or endurance events. And then some of those papers have been reported carbohydrate intakes. Now, what they haven't shown very clearly at all is that those blood glucose levels relating to your carbohydrate intake. There's only been a very small number of studies though, but there's no direct relationship between someone's CGM derived glucose values and their carbohydrate. So someone that's eating more carbs doesn't necessarily mean that their blood glucose will be maintained better than someone that's eating less and they haven't shown that clear relationship yet in a handful of case studies. Yeah.

Taryn Richardson  14:55

Yeah. And those papers are in the paper that you wrote. I think there's five in there and the sample size like the athletes in there are in the range of seven athletes to ten athletes, like one of them even had two athletes. So I think that's just important to highlight because we don't really know yet. There's 5 studies total of 30 people, but good to see that there's some males and females captured in the data, it's not just all males. 

Greg Cox  15:26

And those those studies weren't designed to directly investigate whether or not your CGM derive glucose relates to dietary intake. So observational case studies, in essence, that's reporting on athletes that are actively engaged in ultra endurance event. 

Taryn Richardson  15:44

Hmm, yeah, it's really cool. 

Greg Cox  15:46

Yeah, we've got a paper in review at the minute. And what we looked in at that paper was a group of well trained endurance race walkers so want to be triathletes, let's say. And what we did is we controlled their diet and exercise for two four day blocks, like at the end of two weeks, so days 4 to 7, and then days 10 to 14 and they replicated what they did. And what we were looking at was like when you replicate your diet and exercise, how much noise do you get when you're using CGMs. And what we show in comparison to studies that have been done on healthy, non athlete populations, and also populations of people living with diabetes is that there's less variability. And that probably relates back to their metabolic flexibility so they're able to use different fuels and jump between fuels. And they're also able to use fuels more quickly when they become available. And so that was it really next day.  And that will provide a benchmark, so that if we're doing intervention studies in the future, but what you're basically looking for if you try to create a difference that's larger than that natural variation that occurs. And so they were free living, but it was under standardised exercise and diet conditions and currently in review, so fingers crossed at the minute, but that might come out in the next two to three months. 

Taryn Richardson  17:06

Awesome. They go hot off the press. So what is the lay of the land with using these things right now? Like, any advice for somebody that has bought one and they're trying to implement it into their training and nutrition or somebody that's thinking about doing it, what advice do you have for that person? 

Greg Cox  17:22

I think if you thought about buying one, the first thing you'd want to do is have to invest in trying to understand your exercise. So some of those metrics that you might already have hold of, but also capturing your dietary intake as well. The idea was either conceived why would I want to chase up CGMs and it was to try to understand or spot check like an athlete as to whether or not they were meeting their fueling requirements. So often, you would sit down with an athlete and sort of talk to them about their recent dietary intake. And as a sports dietitian, I might even target in like on a particular heavy training day, right? I want to see are they doing what they need to in and around that training day. And I guess the idea initially, at least was that, can a CGM or the data that's derived from a CGM help me understand that connection better? And what's happening within the exercise session, it might not provide us as much information as we initially thought. That overnight period, we have some pilot days, some of which was included in the review that we already published and some is yet to be released. But there's a suggestion that, like, under conditions when you haven't met your fueling, like so you're in a situation where you've got low energy availability, and I'm sure you've talked about this plenty that that overnight period, you run a bit lower. And so that might be the window that provides us most information about how well you did yesterday. So did you meet what you needed to do from a dietary perspective the day before, rather than sort of understanding what you're doing right now.  So as a dietitian, you've got some subjective information from the athlete, you know about how they performed in the session, you know, how they felt like during the session, how they've recovered? Were they able to completely finish off the session? And then you know, this objective information might provide some extra information to me as a sports dietitian to best understand that. Diving in and buying one, like at the moment depends on how much like disposable income you've got and how much you want to spend. Because like I said, we're only staying to somewhat understand whether or not they have application to people, healthy individuals that have like a normal glycemic response to both exercise and diet.  And I think it becomes even more challenging when you've got athletes that are engaged in really intermittent activities, high intensity, and particularly collision based sports. You can see in your sympathetic drive becomes important and that has implications on your blood glucose response as well. We recently put them on some NFL players to see what happened in an NFL game. And some of the responses that we got, we would never have predicted, like extremely high, sort of glucose levels maintained almost throughout that entire game.

Taryn Richardson  20:29

Cool, how high are we talking?

Greg Cox  20:31

Let's say 15 to 70 millimole.  And all the players in fact maintained glucose levels of 10 to 12 like throughout that period, CGM derived glucose. But you've got to remember that like that's in a fight and flight situation, you got guys running at you. So if you like sticking one on, you know, someone that's helping out in a triathlon in the aid station, and you've got those triathletes running towards that, right? That fear of god you see sometimes, and they're like, just take the cup, don't take me, you know, they might be life threatening situation, so. 

Taryn Richardson  20:48


Greg Cox  21:06

But in response to the onset of exercise, particularly high intensity exercise above 80%, your liver essentially dumps a bunch of glucose into the plasma and then your muscle will take that up, right? But there's a lag period, so there's a bit of glucose that will hang around. And typically, in terms of all your plasma, you're only got at any one point in time about 4 grams of glucose floating around your plasma, that's like a quarter of a banana. So the shuttling, the rate of appearance, and then the disappearance of that glucose, like is influenced by a range of things, not just by what you eat, the intensity of exercise is important, obviously, the duration of exercise as well, how well trained you are will all influence that.

Taryn Richardson  21:51

I think that's really important to highlight - it's not a direct measure of what's going on at the muscle level. So can we talk about, you know, muscle glycogen and CGM use and what are we understanding there by checking our interstitial glucose versus what's actually happening in the muscle? Because I know a lot of triathletes are using them to prevent bonking or hitting the wall. So can you help explain that a little bit better so that people understand that whole interaction?

Greg Cox  22:19

Yes, so with a CGM, we're looking in a window at plasma glucose, in essence, right. And it's about a 10 to 15 minute delay of what's going on with plasma glucose and we're basically looking at the concentration of what's happening. We're not looking at how quickly it's getting taken up by the muscle or how quickly it's being used by the muscle necessarily. So we're looking at like a reservoir and that reservoir is I guess, filled up by glucose. It might be produced and delivered into the system by the liver, or can come directly from the gut into your plasma or interstitial fluid, and then it will be taken up into the muscle.  One of the things that I've really reflected on a lot in my recent career has been the idea that what makes athletes quicker. And one of the major adaptations that occurs as you do more training for endurance training, is you can use fuel faster. And people often think about fuel as you know, your burn lots of fuel in response to exercise. But the way I've come to think about it, it's you're able to use that fuel to go quicker, rather than in responsive going quicker. So your body gets better at shuttling carbohydrate, like into the muscle, and then you actually get better at storing carbohydrate within the muscle as well. And your body then gets better at using that energy or that carbohydrate more quickly. So by using energy more quickly, you can move more quickly, so you perform better.  So if you look at a triathlon, Ironman or Olympic distance, if you look at a slower athlete, and like a faster athlete, they burn roughly the same amount of energy or carbohydrate. But the athlete that goes quicker, they just burn a lot more quickly, which is part of the reason they go quicker. I mean, there's other changes that happen metabolically, in the cardiovascular system as well but the muscular system is major adaptations that occur in response to endurance. And like I said, a large part of that response is the ability to get the carbs into the muscle and also fat for that matter, but then your body to burn that and use that fuel to then go quicker. So like the fuel actually is more important and it's often undervalued because people talk about it in response to the exercise, but it's actually that's the thing that allows you to go quicker, is burning the fuel faster.

Taryn Richardson  24:58

And so do you you need more fuel the fitter and faster you are?

Greg Cox  25:04

In terms of the rate of fuel, yes, you do. Yeah. So you're going to cover the same distance in a quicker time so you need to be more aggressive with your strategy. Someone that's less capable, they're going to burn fuel at a slower rate. So over the course of a triathlon, they might need the same amount of carbohydrate or the same amount of fuel, but they're going to use it at a different rate so you would feed it to them at a different pace. So someone that does an Ironman in 8 hours, they need to get a bunch of fuel in within 8 hours than someone that's doing it in 15, they've got 15 hours. They get roughly the same amount of fuel in. There might be a loss of economy that occurs, like when you're going more slowly, so you might need a little bit additional fuel for that. But in essence, like when you're going more quickly, you need fuel faster.

Taryn Richardson  26:03

This is why I love you Coxy. So you, doing a run would need a crap tonne more fuel than me who sucks at running, or swimming or cycling for that matter? Let's be honest.

Greg Cox  26:13

Maybe like I don't know it's a great comparison. But it's something that people don't think about enough when they're coming up with a strategy. And it's something that has made me really think about how I educate and engage with people and the messaging that I put around fueling. And I think it's a real key component. So just think about that, again, it's your ability to use fuel quickly is part of the rotation that you get in response to particularly endurance training. And that adaptation allows you then to go more quickly. 

Taryn Richardson  26:46


Greg Cox  26:46


Taryn Richardson  26:47

This is what I really valued about our time at Triathlon Australia together is those sorts of conversations and thinking differently, because you know, the messaging out there on the internet is everyone needs 90 grams of carbs an hour. Now currently, it's like everyone needs 120 grams of carbs an hour. But if you stop and think about the practicalities of what's going on, then that makes so much more sense when we're talking to athletes about their individual needs because it's not one size fits all.

Greg Cox  27:13

Yeah, so let's say you go 100 grams an hour because easy math and you do an Ironman in 8 hours so that person needs 800 grams of carbs, they've gone across a certain distance. Someone that's taken 15 hours, you feed them 100 grams an hour, they've had 1,500 grams of carbohydrate. Have you ever looked at what 1,500 grams of carbohydrate looks like? It's a lot of carbohydrate. 

Taryn Richardson  27:37


Greg Cox  27:38

And they've covered the same distance, they've just done it a lot slower. So why would you need the same rate of carbohydrate? And 1500 grams, it's like, you've got to be on the game to be able to consume that amount of carbohydrate because that's a bucket load.

Taryn Richardson  27:55

Let me just quickly calculate how many gels that is. 

Greg Cox  27:58

So 1500 grams, that's 50 gels. 

Taryn Richardson  28:01

50 gels! I know, this is why we're the A-Team because I'm shit at maths and you're good at maths, but I can do colour. 

Greg Cox  28:07

That's it, yeah. 

Taryn Richardson  28:09

Can I segway a little bit? The starch products that people are using for this kind of reason, it's, you know, it's relatable. But people are going to products like UCAN and using super starches because it's better for blood glucose control through endurance events. Do you have any tips and tricks from Coxy's brain on using products like that?

Greg Cox  28:31

Well, essentially, you know, those carbohydrates, the polymers, they'll get broken down through the digestive tract and they get absorbed as either glucose or fructose so they get absorbed as simple sugars. Glucose and fructose get absorbed across different transporters on the gut lining. Some of the larger polymers, they might have benefit, like in terms of hydration. And your blood glucose control in exercise is heavily influenced by the hormones that are produced during exercise as well. I haven't read a bunch in that space recently.  And I often like to forget more than I've learned. That's hard when I'm answering a question like this but you know, your response is mostly influenced by the intensity of exercise that you're exercising at the duration of the activity and, you know, the total carbohydrate intake as opposed to the type of carbohydrate that you're having, particularly, you know, during sustained exercise, endurance exercise that's done at a moderate to high intensity. Those longer, starchy sort of carbohydrates or your polymers, they have to be broken down. They don't get absorbed as large molecules, they have to get broken down to their individual constituents to get absorbed across the gut so they all get into the system in a similar format, despite how you might consume them.

Taryn Richardson  29:54

This might take a little bit longer to do that is kind of where the thinking is at because I know a lot of people are using them in diabetes. Then there's also the layperson, like a general athlete that is on that bandwagon, too.

Greg Cox  30:08

Yeah. And I've never sort of thought about delaying a carbohydrate into the system during exercise. And I say that, like my PhD was done around looking at and investigating carbohydrate intake strategies for high intensity endurance sports, ie Olympic distance triathlon. 

Taryn Richardson  30:25


Greg Cox  30:26

So one of the things that we were the first to show was that in response to consistently consuming carbohydrate around training, so going into a session with high carbohydrate availability, serving a snack, and then being aggressive with your carbohydrate intake during training, doing that for a month, we showed that you had an increased ability to then metabolise that carbohydrate at the muscle. And we took muscle biopsies in one of the studies, and we looked at the transporters, you know, across the muscle that it covered out into the system GLUT4. And we then show an appreciable difference between the two groups in the increase that you get in GLUT4 in response to regularly exercising and that's an adaptation that you get and I spoke about that earlier.  What we theorised was that the ability to use that carbohydrate was because you're able to get it across the gut more quickly. And that was the rate limiting step to being able to use it at the muscle. It wasn't getting them into the muscle, it was getting it from the muscle into the blood, then the blood into. 

Taryn Richardson  31:33

From the gut into the muscle.

Greg Cox  31:34

Correct. So getting it from the gut, into the blood and that was the rate limiting step. And they've done some studies in rodents where they've looked at feeding them, like high carbohydrate chows, right, so by carbohydrate feeds. What they've shown in those studies is they get an increase in the transporters for carbohydrate across the gut and they get an expression, increasing expression for the genes that express more of those transporters. So we didn't take gut biopsies in our study, we have enough trouble taking muscle biopsies. And others have shown that you're able to train that pathway and it's believed in humans that the rate limiting step to be able to use exogenous, so carbohydrate that you consume is across the gut, not the muscle. 

Taryn Richardson  32:22


Greg Cox  32:22

And there's an old study that I think about a lot, not at night, before I go to bed, but like when I'm thinking science, and they have guys exercising a high intensity, really well trained cyclists, you know, they fed them a good amount of carbohydrate, it was like over 100 grams in sort of a 60 minute sort of high intensity effort. And they used about 10 to 15 grams, that carbohydrate was actually used in the muscle in that sort of window of time. And in essence, in an endurance event, like triathlon, you want to try to optimise the use of that exogenous carbohydrate, or the carbohydrate that you consuming.  And so train the way you race, like people talk about that. And part of the reason that you want to do that is to train that system of getting the carbohydrate across the gut. So why you would want to delay that? Like, I'm not really that sure on that, particularly when it's a fuel that you want to provide to the muscle during exercise. And during exercise, your body will regulate your blood glucose response and that's from the hormonal response that you get during exercise. In high intensity, what we've shown at least with CGM derives glucose in sort of team sports where people are trying to run into each other, blood glucose seems to be more variable.

Taryn Richardson  33:39

So in summary, we don't want to be focusing on a lot of the slow digesting, long chain carbohydrate starches because we will really want to try and maximise the ability of our gut to absorb that carbohydrate across the lining into the bloodstream, get into the muscle as fast as possible. We don't want to slow that process down. In fact, lots of products like say, the hydrogel, their whole marketing is to get it into your system faster, but it still has that rate limiting step in those gut transporters. So hopefully, that's an okay summary. A little bit more complicated but maybe steer away from the starches.

Greg Cox  34:18

And there's a good review on that. Louise Burke has done a review in the last couple of years around that, narrative review.

Taryn Richardson  34:25

The hydrogels? 

Greg Cox  34:26

Yeah, and I think that's a great little paper. I think it gets down to type of gel that you like to consume, the practical elements that sit around that. What we do know is people will consume more of something that they enjoy consuming. And so, they're important drivers around you know, when you come up with a strategy as opposed to looking at at rule sort of chemical structure, particularly during exercise, right? Your body responds quite differently when you're not exercising, but it's certainly during exercise.

Taryn Richardson  34:53

Yes. I did get Andy King on to the podcast to talk about hydrgogels, actually. 

Greg Cox  34:58


Taryn Richardson  34:58

That was a total nerd out. I loved it. I'm not sure the listeners enjoyed it as much as me.

Greg Cox  35:03

Yeah, he was a co-author with Louise on that paper, yeah.

Taryn Richardson  35:06

Yeah. All right. So CGMs Coxy, what's the summary? Take home message? Short, sharp, where are we at?

Greg Cox  35:15

We certainly need to do more work. We haven't really done any, or we've just started to do some intervention trials with the technology. There's lots of information coming out. And if you're going to spend some money on trying to refine your nutrition, there's better support at the moment to see a sports dietitian than there is to buy a CGM, right? 

Taryn Richardson  35:38

I didn't pay you to say that. 

Greg Cox  35:39

No, and I'm a sports dietitian. But maybe buy a sample here but like at the moment, if you're looking at, you know, where you spend your money. Now, the difference between the two, right, is that one requires a higher level of investment than the other. But I think one of the things that people forget is fueling with your diet, it sort of makes up 50% of the equation. And so people are happy to invest in a whole range of other tools, and think they can read about nutrition to get individualised advice. So I think you may as well spend in seeking the advice of a skilled sports dietitian, particularly the ones that works in endurance sports.  So are they promising? They might be. If you do buy one, you know, there are options on the internet so make sure you look at your options. And if you're using it, to understand it at the time of use, you want to be tracking your exercise and your dietary intake to get a full understanding of that interaction of the two. That would be my sort of current advice on them.

Taryn Richardson  36:44

Yeah, and from what you've talked about today, is like tracking overnight is a really valuable piece of the puzzle to understand if you've got your day to day fueling and recovery right, as maybe the first step rather than looking at it while you're doing an exercise session, freaking out because you go hypo in 20 minutes, and then shoveling a heap of carbs in.

Greg Cox  37:03

Yeah, and I think if you're going hypo quickly, that would sort of talk to your overall feelings from the day before. And that can also perhaps come along side other body awareness cues that you might get. So if you're one of those athletes that wakes up hungry, you know, two o'clock in the morning. I remember working with a guy that used to do that, eat up and eat like a two milligram packet of chocolate sultanas. I'd say, hey, Jase, you're probably not eating enough during the day dude. And so if you wake up in the middle of night hungry or if you're waking up famished in the morning, like if you stuck a CGM on it, it will probably tell you that you're sort of a bit low and you haven't eaten enough the day before. So a CGM, this real time short delay, they are novel data. We're still understanding what it tells us, you know, in terms of fueling strategies at rest, and also, you know, during sport, so tread carefully. You like your data, you know, sure but if you haven't seen a sports dietitian, make sure you get on that route as well.

Taryn Richardson  38:06

Oh, thank you so much, Coxy. I couldn't have said it better myself. Definitely, nutrition is the fourth leg of triathlon, I talk about that all the time. And there's so many things that you said today that, like that's the way I teach athletes stuff. So you know, your job here is done. You did good. You did good, Coxy. But thank you for sharing all your knowledge and expertise on an area that is just exploding at the moment. So I'll definitely get you back if you come on board, when you've done the next round of research before that gets published so we can get all of the juicy details before it takes three years to get that paper out in press. 

Greg Cox  38:44

Yeah, no dramas. It'd be great. We're pretty close to getting a couple out so you might see me sooner rather than later.

Taryn Richardson  38:50

Yes, I'm excited. Thank you so much, Coxy. 

Greg Cox  38:53

Thank you.

Taryn Richardson  38:55

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! 

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