Aidan:
Hello and welcome to the Ideal Nutrition podcast. My name is Aidan Muir and I’m here with my co-host, Leah Higl and today we are celebrating episode 150. We are now almost three years into podcasting, which is cool. I’m happy with that achievement. So that’s exciting. And what we’re talking about today is whether blood glucose monitors can improve athletic performance.
So starting off with some basics, a CGM or a continuous glucose monitor is a wearable device that tracks your blood glucose levels throughout the day. It involves a small sensor inserted under the skin, usually either in your arm or abdomen that measures glucose levels in the interstitial fluid. Then that sensor, depending on the brand or whatever, will typically transmit that information to a mobile app, which allows you to see your blood glucose meter trends in real time, kind of. We’ll talk about that more. You could see how there could be potential in this space for it to be beneficial. But yeah, we’ll get into it.
Leah:
Yeah, there are a couple of assumptions that we are going to make just for the sake of this podcast and looking at this specific topic. Firstly, we are focusing on athletes with good insulin sensitivity and not those at risk of diabetes. So obviously there is a space where we are using glucose monitoring for diabetes management and that has a wealth of value. That’s not what we’re talking about here. We’re talking about athletes that do not have diabetes and particularly looking at with the intention of trying to improve performance by having this additional data.
We will also most likely be talking about endurance sports more so than other kinds of sports since that is mostly where these kinds of methods are starting to be used. But in saying that the same concepts kind of apply across all areas.
Aidan:
Yeah, you definitely see it crop up more in endurance sports already in particular sports like cycling where like they’ve got really big teams around them and stuff like that. My understanding is like it’s even at a point that like certain races, like I don’t want to quote this wrong, but I’m pretty sure like Tour de France, like they’re not allowed to communicate. Like say they’re wearing a CGM and they’re cycling, the team isn’t allowed to communicate with them being like this where your blood glucose level is at because obviously not whipping out their phones. But the fact that like in training, a lot of them are definitely like doing this.
It’s just hard to say, like we’ll talk through about like whether it’s even beneficial or not. But one way we’re going to start off with is with the potential benefits of this. Bear with us on this because this doesn’t necessarily mean we think there are heaps of benefits. I just want to give a balanced kind of perspective, going through some pros, going through some cons. So with the benefits, there are three main areas that I see as of relevance, which will kind of mean I’m also ignoring some others.
For example, a lot of claims are made about how CGMs could help you optimise fuelling strategies. I would probably pump the brakes a little bit on those claims. We will talk through that a little bit later. But the main three areas of relevance that I see are what if you consistently have reactive hypoglycemia? For example, some people will have some simple carbs pre-workout that leads to a spike in blood glucose levels and then a quick kind of quote on quote crash that could lead to low blood glucose levels.
What if those low blood glucose levels happen to line up with the start of exercise? So you go into the start of your training session or competition in a pretty suboptimal state. You could identify that with a CGM. That’s one potential benefit. Another potential benefit in a way maybe is, what if you consistently had low blood glucose levels at certain times during exercise? Like what if one hour into events you just noticed a common trend that you’re like, I say endurance exercise, you’re like, I have gels here, here, here, and then I just keep having low blood glucose levels here.
What if you identified that and you could address that? That might be more relevant for training than competition. We’ll talk about that as well. But it could also be another additional screening tool for low energy availability. Research has identified that fasting blood glucose levels can drop a bit in response to low energy availability. Once again, this data wouldn’t be a big factor to focus on. I’m also going to talk about how there’s, well, we’re also going to talk about how there could be other ways we could also assess that without a CGM. But those are three things that I look at being like, I can see the benefits to some of this stuff as well.
Leah:
Moving more so into the cons surrounding utilising this kind of blood glucose monitoring in athletes. I’ll preface this with having increases in blood glucose levels is completely normal. There is nothing inherently dangerous or bad about this, even though you may see misinformation online that it’s a little bit fear-mongering in this space. When we eat food that is broken down and converted to glucose, which is released into the bloodstream, and that’s when we see these spikes in blood glucose.
This is particularly relevant to carbohydrates, but I also like to note that protein can also raise blood glucose levels, so it’s not just carbohydrates that can do this. Now, the three cons that we can think about when utilising blood glucose monitors in athletes is one, a lot of athletes, particularly endurance athletes, should be consuming a ton of carbs. And when we’re wearing a glucose monitor, this can make us unnecessarily concerned about where our blood glucose levels are at. And when we see increases in them, this is a non-issue.
But if we’re someone who is consistently monitoring it, we may start to associate carbohydrates with having a negative impact on our bodies. There is also a 5 to 10 minute delay measuring interstitial glucose rather than specifically blood glucose. So the reading that you get may not always be entirely accurate to the specific point in time at which you’re receiving the data, which can be an issue depending on how you’re actually deciding to use said data.
Of the most common machines available in Australia, one takes samples every minute, which is great, but others can take samples as infrequently as every 15 minutes. So you can imagine if something only was taking that data every 5, 10, 15 minutes, combined with the delay that you get using interstitial blood glucose data, the relevance of use starts to get lower and lower and lower. So that’s just something to consider as well from a data point of view.
Aidan:
So from what I have seen, most people in sports seem to be using, in Australia at least, seem to be using that one that does send out every one minute. Because as you can imagine, these people are pretty switched on. Like the people who are using this are smart people in most cases. I say that very loosely like some people can be very intelligent and misguided but like the people who are using this typically are quite smart people and they’re trying to absolutely optimise performance so they’re gonna get the best of the best they’re typically using the ones they’re sending it with about one minute of data like data every one minute.
The five to ten minute delay thing is still relevant from that interstitial glucose to blood glucose something that I touched on a little bit earlier about the whole what if you kept getting lows at a certain point? Well, what if the CGM just kept giving you data that’s five to 10 minutes late? You’ve already been low. Like you’ve already been low by the time that you’re getting that kind of notification. So that kind of decreases the relevance a little bit. I’m not gonna say that ruins it, right? It still can be useful, but like it’s, it decreases a little bit. I’m gonna go through some more nuanced thoughts on this that will come back to the thoughts and the benefits.
So the three benefits I focused on were reactive hypoglycaemia, low energy availability and also the potential lows during training. So going through one at a time, I think the reactive hyperglycaemia aspect is relevant and the other two ones really aren’t. There could be other ways of doing the reactive hyperglycaemia, but this does seem to be the easiest way to kind of identify that. The low energy availability thing is something that we should be focused on trying to avoid anyway.
Like there are also many other signs. Fasting blood glucose levels can also be measured in a single measure too. It doesn’t need to be a CGM. Like if you’re like, hey, I really want this data because it is useful to have heaps of data points. Fasting blood glucose levels, you can just test fasted once off, that gives you a fair assessment.
So if you were testing that daily just as a single measure and you notice that that started dropping, that’s a bit of a sign amongst many other signs of low energy availability. So it doesn’t need a CGM for that. The one about going low at specific times. If we look at this from a competition perspective, with all the endurance athletes I work with, I’m trying to give them as many carbs as they can tolerate during endurance activities at high intensities when they’re competing.
Like if somebody was having 60 grams of carbs per hour, but they could take on 90 grams of carbs per hour, and it wouldn’t negatively affect their performance, like they wouldn’t have gastrointestinal distress or whatever, I’d get them up to 90. I would give them more. So like, what if they were having, they’re just following my guide as much as you can tolerate, and then they randomly were having lows still.
We can’t just add more, like we can’t just add more. And the other thing is I was looking at like a bunch of research just on like, ultra endurance runners and stuff like that, that was kind of relevant for this point where it seems like their blood glucose levels are relatively stable throughout ultra endurance activity. There was other research that I don’t know if we’re going to add this to show notes because I am just, I didn’t put it into our thing for our content guys.
But I was also looking at other research on cyclists where it did seem to be like their blood glucose levels would increase every time that they did eat. But the point about that ultra endurance one was just that like, the researchers were having a bit of a reach and being like, well, we can say that people who maintain slightly higher blood glucose levels actually did perform better.
But that’s also kind of like saying the people who took on more carbs performed a little bit better. So we’re still trying to do the same thing in many cases. I’m not gonna rule that out as something that there would be no benefit to this whatsoever, because there could still be a little bit there. But I just don’t think it would change much.
Leah:
Let’s talk about from a more nuanced perspective, because if we like anything on this podcast, it’s a bit of nuance and talking through the shades of grey, but thinking very open-mindedly about how blood glucose monitoring could be valuable. If there was zero chance that this would negatively impact an athlete, could we just use this as literally just another piece of data to have amongst a whole heap of other data?
Aidan:
So that’s exactly it because like one of the reasons why I’m so hesitant with this is because it typically like it will lead to a lot of negative experiences for people. But yeah, thought experiment. Let’s say that that didn’t exist and we could just think about it without that being the case. Earlier, no, not this year, I think it was like late last year, I went to sports Dietitian’s Australia conference and something that I really like about high level sports dieticians is that they seem to be on the cutting edge in a way in that like I see a lot of dieticians being very like myth busting focused.
Whereas a lot of these high level sports Dietitians seem to be like, now let’s try some stuff. Yeah, it does or it doesn’t help kind of thing. I’ve seen that in other areas. For example, like in 2017, I remember being at the AIS and they were using bone broth with the belief that maybe this will help with injury recovery. They later came to conclusion that has inconsistent amounts of collagen and maybe it’s not the best option, but like, at that time, I remember every other dietitian I was around was like, no, bone broth is a myth. Yeah. They were just kind of like, let’s try it because either it helps or it does nothing.
Leah:
Pickle juice is another one.
Aidan:
Yeah, pickle juice is another great example. Yeah. But at this conference, they were doing a lot, they were talking a lot about CGMs and they’re sharing a lot of opinions that we’ve kind of already mentioned as well. But there was this one, one presentation from Asuka Yukonjop, who does work with a lot of high level cyclists and in a lot of other sports as well.
He used a really great analogy that hit home for me, where he was like, comparing it to other advances in sports technology in a way. When heart rate monitors came out, a lot of similar conversations went on where they’re like, does this really help us? Like, like, honestly, like when heart rate monitors come out, you’re like, how does this help us? Like, I know when I’m like, absolutely redlining, like I’ve got a high heart rate, I know when I’m taking a bit easier, like I’ve got a low heart rate. But like, does that do anything?
Now in 2024, a lot of people do adjust their training based on their heart rate. That’s another deep kind of conversation. But at that time, it was just another piece of data that didn’t really have any relevance or application at that time. The logic that he kind of uses is like, if there was no negative for athletes, and it didn’t do anything for them negative, could this just be another piece of data?
And then if we collected heaps and heaps and heaps of data through this stuff over time, could we then find a use for it? Just like some people would argue that they have uses for heart rate monitors now. Interesting that like there’s a lot of caveats. But like I did kind of like that angle about being like, he was just being like, imagine we could just get athletes and they didn’t even know they had this on and then we could like, but there’s flaws in that obviously.
Leah:
Yeah, like realistically, I think if we didn’t have maybe that fear around blood glucose and blood glucose spikes in the general public and even amongst athletes, it could be something like you’re tracking your sleep, you’re tracking your steps, you’re tracking your heart rate. Like it could just be another data point. But I think in a lot of cases, because of preconceived notions around blood glucose, at least with how things are currently, this could lead to some issues with athletes maybe changing their nutrition in a way that is negative rather than beneficial.
Aidan:
We see this in practice heaps. So there have been many practitioners who’ve just tried to solve this problem just by like education. Like they’ve just talked through the athletes being like, don’t worry about it going high at certain times. Like that’s not what we’re looking at. But using a real example that also just came from that same presentation from Asuka that I just like, I found this just interesting was he like set up some experiments with some athletes where they were trying to blood glucose monitors. He went through this whole thing, like explaining a lot of the stuff that we’ve just kind of talked about.
And he was like, yeah, these athletes are on the same page. They’re going to go away. They’re going to do it. And he thought things were going well. One of the athletes came back, thought things were going well still. And then out of nowhere, the athlete was like, yeah, I didn’t realise orange juice is so bad for me. No, that’s not the takeaway. It’s like, every time I have it, my blood glucose levels just spike. So I’ve stopped having orange juice. And he’s like, that’s not what we’re doing.
Particularly with some of these athletes where we’re trying to get like really, really, really high carbohydrate intakes, you are going to see spikes. And almost every time you will likely work with an athlete no matter how much you brief them, all of these kinds of things, there is a very high likelihood that you would be giving them these high carbohydrate targets, you’d give them a CGM, and then suddenly they’re looking at it and they’re seeing the blood glucose levels go up. And they’re like, inadvertently suddenly decreasing their carbohydrate intake to try to avoid these kinds of things.
Whereas we know that those high carbohydrate link, high carbohydrate intakes are linked with improvements in performance. So like, it’s all good in theory for us to be like, let’s do this thought experiment, but it’s so hard to apply.
Leah:
In application a lot harder. Yeah. As a little bit of a summary, the current consensus is that continuous glucose monitors for athletes without diabetes does come with risks and doesn’t really improve performance. Like, we are not really sure how to utilise this data in an effective way just yet. So given that there are risks there, it probably doesn’t make a huge load of sense to be utilising it widespread. I’m personally interested in the reactive hypoglycemia thing. And I know you would be too here.
Aidan:
Yeah, 100%.
Leah:
Yeah. I think that is definitely an application where this could be useful, but at this point in time, it’s not something we are widespread telling everyone to go and do.
Aidan:
Also doubling down on that point, something that I don’t know if you’ve had this experience with people, but like a lot of people over the years who I’m just working with, like they’ll just drop a line in consults where it’s like, oh yeah, I had a low blood sugar. So I had some lollies and that perked me up. Yes. And my, particularly if they’re on a plan and that has taken them off the plan. My first response to that and this, I don’t know, like it’s a true response. My first response to that is, how do you know you were low? Like that doesn’t mean what they felt isn’t true.
Like what they felt is true. But I’m like, how do you, how did you know that you were low? Did you test? Is this something that happens often? If this is something that happens often, can we test? Like, can we just like, and in those cases, I’ve just been talking about like a single finger prick, like you wait until you get the symptoms test and see. Cause in many cases in those scenarios, they’re not actually low. But my interactions with people who have done the CGM things, like just like a bunch of other sports dietitians who have just tried it on themselves is that they actually have gotten a few lows here and there, and it has lined up with how they’re feeling. And it actually has changed what they’ve done.
So I’m interested in that reactive hypoglycaemia thing, but the one thing that I would really push is I wouldn’t explore this if you’re not getting symptoms. Like, because the other thing is like, I would also say that a lot of people might actually get low blood glucose levels at certain times throughout the day and not have any clue of it. And if you don’t have any symptoms, totally fine. Yeah, we even define hypos in people with diabetes as, depending on definitions, below four millimole per litre and experiencing symptoms. If somebody was like 3.6 and they felt great, we wouldn’t define that as a hypo. But sometimes if somebody had complete access to that, they would freak out about that as well, which I understand, but it’s also like, that’s what I’m saying, wouldn’t test this if you didn’t have symptoms.
Leah:
This has been episode 150 of the Ideal Nutrition Podcast. If you haven’t yet left a rating review, it’s so greatly appreciated when people do that or do things like share us to your Instagram stories and tag us. Love to see it, but otherwise, thanks for tuning in.