The Wellness Scoop - The Extra Scoop: The Truth About Glucose Monitors

Episode Date: May 15, 2025

Continuous Glucose Monitors (CGMs) have exploded in popularity, promising everything from weight loss to personalised health insights — but are they really delivering? To help us make sense of the science, we’re joined by Dr. Javier González, Professor of Nutrition and Metabolism at the University of Bath. Javier recently co-authored a study exploring how CGMs impact non-diabetic adults, and found that they might be giving misleading feedback and even encouraging unhelpful dietary choices. In This Episode, We Cover: Blood sugar 101  What CGMs are and how they work The key findings from Dr. González’s recent study Common myths and misconceptions about glucose tracking. Are CGMs actually beneficial for people without diabetes? The risks of relying too heavily on health tech Simple, science-backed strategies for managing blood sugar — without a monitor Live Show Tickets - ⁠⁠⁠⁠⁠https://cadoganhall.com/whats-on/the-wellness-scoop-with-ella-mills-and-rhiannon-lambert/⁠⁠ Learn more about your ad choices. Visit podcastchoices.com/adchoices

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with top experts, so there is no fluff, just facts. Exactly, it's all quick, practical, evidence-based advice to fit into your busy lives. So this is the Extra Scoop. Let's get started. As our listeners may know, our Extra Scoop episodes are all about taking those topics that everybody is talking about and quickly breaking them down for you so that you have expert-led insights that leave you informed and empowered when it comes to your well-being. Now this week we are talking about something that has absolutely exploded in the wellness space recently and it's the use of continuous glucose

monitors or CGMs as we'll probably refer to them today and I attended a wonderful talk a few weeks ago where I saw our expert speaker today. So to help us unpack the facts, we're joined by the wonderful Dr. Javier Gonzales, the professor of nutrition and metabolism at the University of Bath. Now Javier recently co-authored a super interesting study that looked into how CGMs impact non-diabetic adults.

So remember, these are targeted at the entire population at the moment, it seems, even though they were obviously invented for diabetics. And he found that they may actually be giving misleading results and potentially encouraging, well, encouraging unhelpful dietary choices and shifting how people view their health. So we're so excited to have him on the Extra Scoop to share the insights and help us make some sense of it. So thank you, Javier. Thank you for having me. Yeah, delighted to be on the podcast today.

Can we start at the top if you don't mind, Javier, because I'm sure pretty much anyone listening has heard the term blood sugar, has seen someone talking about a blood sugar monitor or seen someone wearing them. But I think it would be very helpful just to get a 101. What are we talking about with blood sugar? Why does it matter? And what are these glucose monitors? Yeah, I think it's a great place to start. So our blood sugar is blood glucose concentration.

So the main form in which the sugar circulates in our blood is in the form glucose. It's a really important fuel for many of our body cells, and in particular our brain. Our brain is a major consumer of glucose. That's partly why it's so important to measure the level of sugar in the bloods for people with diabetes. They need to keep their glucose sufficiently high that the brain has enough fuel. If that goes too low, then that can be very dangerous indeed. People can enter into a coma, for example, if the brain isn't getting enough fuel from sugar. On the flip side, if we've got too high blood sugar levels, then that can cause damage in the long term. So, if we've consistently got high levels of blood sugar, that can damage things like the long term. So if we've consistently got high levels of blood sugar,

that can damage things like the blood vessels around our eyes that can lead to things like blindness. It can damage the blood vessels around our kidneys and cause kidney disease, and it can damage the large blood vessels and lead to cardiovascular disease or heart disease. So we want to keep our level of sugar in the blood within a healthy range. For most people, that's not a problem. We don't really have to think about it. But for people with diabetes, of course, that's the main challenge of their condition. These monitors were developed to help people with diabetes better manage the levels of sugar in their bloods. Previously, people would have to perform these finger prick tests where they'd

pierce their skin on their finger and take a small drop of blood and measure the concentration of sugar in that blood droplet. That's of course just annoying to have to do to keep having to pierce the skin there. And so these monitors have made great advances for people with diabetes. But it's important to remember that they're not measuring in the blood itself. So what we want to know is the amount of glucose that's in the bloodstream that our brain is going to be exposed to, that our other tissues are going to be exposed to. But the way these devices work is they measure glucose in something called interstitial fluid. And that's the fluid that bathes our cells. It's not directly

in the bloodstream. And so there's one level of difference there between what's circulating in the blood and what these devices are measuring. And so they try to correct that by using algorithms that are proprietary. So we don't really know exactly what the companies are using in their equations here. But they use these algorithms to try and estimate what the true blood sugar level is. And that's really challenging to do for two main reasons. One is there's a time lag between what's going on in our bloodstream and what's going on in the interstitial fluid. And also just the absolute number differs as well. So the concentrations we get differ. And so those two differences

are mainly why these devices aren't perfectly reflecting what's going in the bloodstream. Now the degree to which we get this difference then really depends on what you're using them for. So for example, for someone with diabetes, they might have big swings in the range of glucose that they see. And so a small difference in the measurement error doesn't make so much of a difference to the way they use the monitors because they're dealing with very large fluctuations in blood glucose. Whereas for people who don't have diabetes, we keep our blood sugar levels within a very narrow range anyway. And so small measurement errors make a bigger difference to how we might interpret the values that we get.

I mean, you've summarized it so perfectly there. So it helps our listeners understand it really isn't black and white. It's not on 100% accurate reading. If you put a CGM on your arm or wherever you're placing this, you're most definitely not going to get a number that reflects what's happening in that exact moment in your bloodstream. Is that what you're trying to say as well? Mason- Exactly. Yeah. So no device is going to be perfect, but the degree of the imperfection that is relevant really then depends on the person and the use that we're trying to apply these monitors to. Emma- And then if we have a think about the fact these are used in programs, weight loss

programs, they're used in a variety of different ways right now. You obviously worked on a paper with Bath University. Shout out to Bath, by the way, because I grew up near Bath in a town called Melksham and I used to go to bath every weekend. And I've done one lecture at Bath, you know, I did a visiting lecture a few years ago. So love it there.

And the research you did, it was kind of like a sigh of relief for the scientific community because we've been seeing these links between blood sugar and weight loss. There have been explosions of popular social media accounts talking about glucose all the time. Could you just delve in a little bit and explain why you think these CGMs have been placed in weight loss programs to start with. Will Barron I think one of the reasons is the idea that a food that might be healthy for some reason, so for example,

foods that might be slowly digested and absorbed and release the carbohydrates slowly into the circulation, should produce a lower blood glucose response to that meal. And I think people then maybe oversimplify it by thinking that if a food is healthy for one reason, such as reducing our blood sugar levels, it must also be healthy for all other reasons, including things like weight loss, when weight loss can be completely separated from our blood glucose concentrations. Can I ask a question on that? I don't want to be reductive in my question, but it feels like listening to you speak on this, certainly where we are in ICI and a lot of the conversations that we have, a lot of the reason this show exists is we feel like the conversation

around health and wellness has become very reductive, very sensationless, and has steered us quite a long way from the foundations and the kind of basics of health. A balanced diet, going for walks, managing your stress, except the boring stuff, essentially. And when I listen to you talk, the thing that I take from it is that it feels like this is very symptomatic of this desire that we have at the moment for continuous self-optimization. You know, I eat a balanced diet, but let me put on a monitor so I can make it perfect. Let me try and be perfect. And in the pursuit of perfection, A, it's highly stressful, but you're saying it's not even accurate. So you're stressing yourself

out and then you're having an accuracy. And to your point as well, like for most people who are eating a healthy diet, that healthy diet or healthy-ish diet keeps their diet naturally and their blood sugar in the healthy range. So they don't even need to be thinking about this. So to me, it feels like what we're talking about here is highly symptomatic of an industry that has become quite reductive,

where to your point, one thing equals all else. So, you know, a healthy diet means it must be weight loss, it must be X, it must be Y. And it's becoming this highly reductive way to talk about what is so complicated in terms of nutrition, food, science. Toby So, absolutely. And obviously, I'm speaking as a scientist who ends up studying things with a bit of a reductive way. But then the way I live my life isn't that way. I think that's the way people should try to view things. I think one of the best phrases that might summarize part of the point you're making there is, we can do things imperfectly right or perfectly wrong in the sense

of these devices are helping us maybe achieve that perfection, but if they're not measuring things with the perfection of accuracy, then we're getting it wrong. There's also another element to this, which is the focus on a single metric. One of the problems with solely focusing on glucose as the only health outcome is it can lead to dietary choices which have other negative health effects. Probably the easiest example of this to think of is the easiest way to keep someone's glucose perfectly flat would be to avoid all carbohydrates. To go on a very low carbohydrate diet,

which might happen to be high in saturated fat. We and others have done similar studies where we do this. In those scenarios, people's LDL cholesterol, the cholesterol that causes cardiovascular disease tends to increase. They might be seeing their blood sugar being perfectly flat and thinking this diet is very, very healthy, but other things under the bonnet that they're not measuring could be actually causing harm. And so the reductionist simplified view of only focusing on one metric has other potential downsides as well. Absolutely. This is just it. You cannot measure health in one single way. There's a lot going on that you can't see that's happening. Could you break down the findings from your research? Because I remember you also spoke about the variability when you eat the same food at different points each week with the readings. It was absolutely fascinating.

Toby I guess it may even be worth mentioning that there were two studies that came out in the same journal within a couple of weeks of each other. So there's ours and there's another one that did a similar thing comparing two different CGMs. And the previous paper found very big differences in how the CGMs would rank order different foods. If we're talking about foods that might lead to the highest blood sugar response versus those that lead to the lowest blood sugar response, depending on the device you use, you would get very different answers. Then what our study did was, in addition to having a CGM, we had the kind of criterion method of using the finger stick

sampling. So that's kind of using that as the reference method. And we used a system known as the glycemic index testing system to classify the foods that we tested. So what that does is it uses pure glucose as a reference. So people drink 50 grams of pure glucose and we measure the blood glucose response to that ingestion of pure glucose. And that gives us a value of 100. If we then have a food that raises our blood sugar level to just

half that of the pure glucose, then that's 50% and we assign that a value of 50. And you can use that to give all different foods a different number in terms of their glycemic index. If they have a glycemic index of 100, they raise blood sugar levels to a very high level, to the same extent as glucose. If they're low glycemic index, then they tend to be below 50 or so. What we found is that compared to the finger prick sampling, the gold standard or reference method, the CGM tended to overestimate blood glucose levels on average, but it also seemed to misclassify the glycemic index of several different foods. So, not only is it just off in an absolute sense, it seems to be proportionally off for

certain foods and not others, leading to this misclassification. And that was in a non-diabetic community, the research of course. That's right. Yeah. So to anybody listening, this is still a very helpful device for type 1 diabetic or anybody that, you know, this can really be fantastic for them because the variability can be so high. But for most of us, it's just wildly inaccurate. Mason- So I should also emphasize that we have used these CGMs with great effect in some of our

studies in non-diabetic populations, but more to capture overall dietary patterns rather than specifically classifying different foods. So what I don't think these devices have the precision to do is to be able to say, for me, this banana is going to raise my blood sugar more than another meal. I think that's the degree of precision that they lack, they don't have. But just is my general diet leading to a very high or a very low blood glucose concentration, I think that's where they can be still useful. That's a really helpful differentiation where, you know, potentially for people who are generally struggling with their health, potentially they're struggling with their weight and they're

in the pre-diabetic range or something that to your point, you could use it to get an overall sense of a picture over a period of time that could be helpful in making kind of much larger changes and improving your health. But for people who are the worried well, essentially, if we're be transparent about it, who generally eat quite well and who are generally well, it feels like it becomes an unnecessary stress and one-dimensional view of looking at their health. I think one of the things that I'm very conscious of though is that these graphs are really visually appealing. There's a lot on social media where you see, if you have a smoothie, it will do this to

you. If you have a, and I'm talking about therefore like vaguely healthy things, a banana on its own to your point, it will do this. It all makes it look quite terrifying. I worry that it's creating a real fear of food. I was just curious what your take is on that. Mason Hickman I agree. I think certainly the visuals are very emotionally impactful. I do wonder if we can harness that for good rather than... I agree that I think at the moment it probably leads to a negative perception of foods. But I wish we could harness that emotional response to get people interested in nutrition and interested in the science. At the moment, we're not doing that effectively. I'll probably add actually that the peaks that

you see after the ingestion of meals there, the big spikes look scary. That's one of the other things we explored in this study was if you just take that peak, that's in particular where these devices seem to overestimate things. They overestimate the time that people spend in this high blood glucose range by more than twofold and up to three to fourfold. by more than twofold and up to three to fourfold. They're overestimating it and giving a greater perception of danger than probably truly exists, again, with the caveats within this population and within the meals that we tested. Of course, every graph you see. I think I know the particular ones Ella's discussing on social media. They were just one individual showcasing their own response to food. I mean,

everybody's response is going to be slightly different. And didn't you say you have to test something, wasn't that up to 70 times to get an overall average that you could potentially view as valid? Yeah, exactly. And that's because we do differ between one another, but we also differ to ourselves yesterday. So if you want to know how we respond individually to a certain diet or food, we still need to replicate that multiple times within ourselves to get a true picture. So yeah, these aren't easy to do. And the way in which you see some of the social media experiments take place seem to be overly confident is one way I put it.

MS. MCNAMARA It is is overly confident. I'd love to have your view because I don't think we can deny that health tech is going anywhere. Health tech is probably the future and there's pros to it of course. It can make access to healthcare more accessible for so many people on a broader level. It potentially could help reduce NHS times. I don't know. There's a lot of talk from these different health tech apps at the moment. There's a lot of them in existence. But what is your overview? Do you think we're ready for personalized nutrition?

Do you think we're at a point where, or are we kind of using the car as we're building it or whatever that saying is? Yeah, I think we're probably not there yet. I think the technology is a great tool to have and to help on the path towards personalized nutrition. But I think we also need to improve study design as well. I would like to think in 10 years' time, we might be closer, but we need all of these things to improve at the same time.

So it's study design. It's actually how we analyze the data we get, the huge data sets and the same time. So it's study design, it's actually how we analyze the data we get, the huge datasets and the technology itself. And I'm definitely keen to try to improve the values we can get from these devices and others. And hopefully some of the work, the current work we've published and the work we're doing at the moment can help us understand why we see these differences in people who don't have diabetes. If we can understand the physiology behind that, we can improve algorithms and measurement methods

going forward and hopefully solve this problem. And if people are listening to this, they're probably thinking, maybe I don't need to sign up for one of these at the moment. To your point, potentially in the future, it could be a really helpful part of a kind of total picture of personalized health. But as it stands, it's probably for lots of people not necessarily the best use of their time and money at the moment. If people are though thinking about, okay, looking at my diet, what are the best couple of interventions

or steps I can take to just support keeping my blood sugar for the most part in that healthy range. Do you have any words of wisdom? Yeah, so I guess I hope it doesn't sound boring, but the general recommendation to eat a higher fiber diet is one way to keep your blood sugar under better control. Another one is to select those low glycemic index foods. So there are databases available online where the degree to which different foods raise blood glucose levels on average has been reported in peer-reviewed studies. Glycemicindex.com, I think, is the website where you can just search those

databases. This also relates to the last question, actually, where I think the benefits we would get from precision or personalized nutrition over and above these generic recommendations is probably very marginal anyway. So even if we could do it right now, it's questionable the extra benefit we would get over the general advice to eat a diet rich in fruit and vegetables, generally higher in fiber, and lower glycemic index, your kind of complex carbohydrates as foods. It's really helpful advice that anyone can go and look that up. And also, I remember you mentioning about cycling. So you're an avid cyclist, is that correct?

Yeah, although I say less so now. I'm running more recently due to lack of time, but yeah, certainly was a cyclist and have worked in pro cycling. And you mentioned looking at nutrition, of course, for athletes, as we know, it was a cyclist and have worked in pro cycling. Emma M They're currently not permitted in competition. One of the ways in which they could be useful, for example, is when athletes do very high-intensity exercise, that causes our liver to release glucose into the circulation to provide extra fuel for the muscle. If your liver is depleted of its carbohydrates store, then it's not able to do that as effectively. And so with careful testing, you can get some crude measurements of what might be going on in with the physiology of an athlete by using these monitors alongside specific types

of training. Yeah. I mean, watch this space Olympics in 10 years, maybe everyone's going to be using CDM and it's going to be gone from our public health health tech. Who knows? Yeah, possibly. Well, this has been so helpful. Thank you so much. I feel like that's given people such a thorough understanding. And I think our big aim is trying to kind of simplify all the noise for people in terms of what do they actually need to do. And I loved that your answer to the question in terms of people's diet that you started

it was saying I know this is quite boring because it's just what we come back to time and time again is like the fundamentals for people's long-term health and wellness is quite boring and it's much more fun to track stuff and it's much more fun to get graphs and it's much more fun to kind of put things in camps of good and bad because it's just a lot more interesting to some extent and clickbaity than it is to say well try and get more fiber and bad, because it's just a lot more interesting to some extent and clickbaity than it is to say, well, try and get more fibre in your diet. It's also a financial gain, Ella. Like think of the financial gain in the wellness industry

to showcase these things as being exciting and savvy. Like they must, you know, they rake in a fortune. But also in such a complex industry, I think it's really tempting. And I totally understand why people want to try this because to have something to tell you what to do, I think is a very human approach. As I said, it's such a complicated industry and it's so nuanced and there's so much noise. The idea that this single thing can tell you essentially what's good and what's bad and

you can live by that is a very appealing concept. So I'm not surprised that it's had so much hype. I think it's just important to see that it's not necessarily there to be such a marker and to live by at the moment. And they're very, very expensive. Emma Cunningham Would you say, Javier, it's behaviour change as well? So it just helps enforce a behaviour change to have a visual on what's going on? Javier Mase helps enforce a behaviour change to have a visual on what's going on? Will Barron Yeah, I think it's a really useful tool to engage people in a behaviour change. But that's where the support of a dietitian or healthcare

professional to really ensure that that change is a beneficial one is crucial. Any type of impactful measurement, and this is where these are the epitome of that, because in real time, you can see what's going on in your interstitial fluid or blood, then that's the power that it has. But it's really how we can use that to benefit really. So to round up, just to reiterate to our listeners, you know, you don't need to be scared of glucose spikes. No. So certainly within that healthy range, there's not really any good evidence that they cause long-term harm. So yeah, if you see a small spike after a meal, that's perfectly

normal. So validating, so helpful. Thank you so much for your time today. We so, so appreciate it. Thank you for having me. Thank you guys so much for listening to us on the Extra Scoop. We are a community-based podcast. We want this to be helpful for you. So any requests, we want to hear it. Absolutely.

Let us know which experts that you want on the Extra Scoop. And we will see you on Monday. Can't wait.