Aidan:
Hello and welcome to episode 228 of the Ideal Nutrition Podcast. My name is Aidan Muir. I’m here with my co-host Torwen Eerkins. And we are going to talk about whether continuous glucose monitors are useful in healthy people. We are going to start with background on how blood glucose monitors work. We’ll cover overall glucose metabolism. Then we’ll talk positives and negatives. So, we’ll give a balanced take on using them without type 1 or type 2 diabetes.
Torwen:
Yeah so, continuous glucose monitors are wearable devices that track glucose in interstitial fluid under the skin. You can wear them 24 hours a day. Typically that is seven to fifteen days before replacement. They send information through a transmitter to your phone. Then you can see all the data. Now, some devices can also link to an insulin pump. You can control that from your phone as well. Which is pretty cool.
Aidan:
Yeah, it’s cool to get this data throughout the day. I think it’s a big step forward with technology. At a minimum, it makes diabetes management much easier. The insulin pump link you mentioned is exciting. What a time to be alive compared to how hard that used to be. That’s exciting.
Torwen:
Let’s chat about overall glucose metabolism. That helps everything we talk about make sense. After you eat, carbohydrates break down into glucose which enters the bloodstream. This leads to a rise in blood glucose levels. The pancreas releases insulin to help cells absorb glucose. Which again, lowers blood sugars back to normal levels. Now, your blood glucose naturally fluctuates through the day. Food intake and exercise influence those changes.
Aidan:
So we’d say normal fasting blood glucose is about 3.5 to 5.5. Maybe even six in some healthy cases. That assumes no major insulin resistance. It assumes no issues with the pancreas releasing insulin.
When we eat, obviously glucose levels go up. Carbs break down into glucose. Sometimes protein breaks down into glucose as well. In normal metabolism, you see spikes, then dips back into the healthy range. For example, a 100-gram carb meal is not uncommon for athletes. Glucose could move from about five to nine mmol/L.
It might peak after 30 to 60 minutes. It then returns to baseline within two to three hours. That pattern is like, super normal. You could avoid it by going lower carb. Carbs benefit a lot of athletes. With insulin resistance, the rise might last longer. If it stays elevated for long periods, issues can arise.
Torwen:
Before we jump into the positives and negatives, I just want to touch on this. These monitors sit in interstitial fluid, not blood. Glucose first hits the bloodstream and raises blood glucose. It takes time to leak into interstitial fluid. That’s where the tracker sits. So there can be a lag. And we see that on the monitors.
Aidan:
Yeah, it’s common for a five to fifteen minute lag. That has implications for some things we’ll talk about. Some devices are a little quicker. The standard is still five to fifteen minutes behind. So, we’re going to talk about positives and negatives. And we’ll start with positives, then negatives. Many dietitians lean negative for healthy people. I still want to start with positives and see what we get anything from that.
A potential benefit is reactive hypoglycaemia, especially in relation to pre-exercise fuelling. Some people have simple carbs 30 to 45 minutes before training. They spike, then dip, and the dip hits at the start of exercise. And this may raise more questions than answers. Because, in isolation, that looks terrible. Research on pre-exercise carbs often finds neutral or small benefits. Some individuals still have negatives and fit this category.
Where I view this as a positive is what if someone suspects this, they could check with a CGM. Or they could also test blood glucose in general. If the pattern aligns, they could change strategies. They might move carb timing or change the form of carbohydrate. I could see a potential benefit to playing around with some strategies there.
Torwen:
Especially for athletes, it’s important to have higher glucose before training matters. And we know that a low at the start affects performance and how you feel. A CGM could detect this if you get dizziness, weakness, or fatigue after pre-training carbs. Another one I want to talk about is that people have random overnight hypos. Many people have them without realising it. A wearable can reveal hidden hypoglycaemic episodes during sleep.
Aidan:
Yeah, and a key point here is that it only matters if it matters. If you sit at 3.4 mmol/L and nothing goes wrong, it probably doesn’t matter. We define a hypo as below 4 mmol/L and having symptoms. If you wake with symptoms and waking up in the middle of the night, testing may help. Maybe you’re waking for other reasons.
Maybe it’s glucose. If you test, now you’ll know. A very cautious positive is identifying individual responses to foods. Glycaemic index responses vary between people. So, early research shows noticeable individual variation. Some foods called high GI were low for some people. Some low GI foods were high for certain people. So we know there is individual variation. Theoretically, if that mattered, you could see it at an individual level. The upside might be small.
You must be patient interpreting data. Many factors skew readings, like illness or stress. A one-off high might be other variables, not the food. Some people may become cautious around foods unnecessarily. If you just gathered information, there could be a cautious benefit.
Torwen:
I think that leads us to the negatives. It can create a general fear of carbs. This could be in athletes and non-athletes as well. Also, people can become obsessed with stable blood glucose levels. If you test specific foods, you might fear those foods.
Aidan:
It can create a lot of fear. There is research on pro-cyclists on very high carb diets. Data collection was meant to be neutral, like early heart-rate tracking. They still came back saying orange juice is bad for them. Tour-level cyclists all eat very high carbs. Even lower-carb proponents still eat a lot of carbs. You don’t really want that fear around carbs when that is common to performance.
Other downsides include cost. And there’s potential to misinterpret your own data. Then three, the delay. This could have huge implications in sport. Real-time strategy needs real-time data. If you’re fifteen minutes behind, is the data useful? A reactive low fifteen minutes ago can’t be fixed instantly. You’d use trends and adjust going forward.
Torwen:
Yeah, I agree with those negatives that you’ve mentioned there. Another risk is becoming overly cautious with simple carbs. When you mentioned that orange juice being “bad for me” as it may spike glucose faster. That doesn’t make it bad. Are we using it in context? Yes. So, the fear mainly targets fast-acting carbs. Is there anything else you’d like to add?
Aidan:
I don’t think so. I think we’ll go to our overall thoughts. Do we recommend it? I’ll let you start with that one.
Torwen:
Yeah, this is something I have never recommended so far. And I’d be hesitant unless there were clear indications. That could include athletes with hypoglycaemic episodes. It could include other conditions where blood glucose levels drop low.
Aidan:
What if someone has newly diagnosed type 2 diabetes?
Torwen:
I mean, it could be interesting. Regardless, you might look at the diet first. Are you able to change the diet? Then would you look? Or would you look proactively to guide changes?
Aidan:
Yeah, I’m on the same page. If someone is interested and level-headed, that helps. They shouldn’t freak out about every spike. They should be well-informed or work with professionals. If they tick those boxes, I’m on board. If not, I’d steer them away. But it’s different with type 1 diabetes or an insulin pump. But, once again, I wouldn’t recommend it to many healthy people. I’ve seen dietitian friends use it on themselves. And some found reactive hypoglycaemia and other things. That’s cool to see, but that’s a very niche subset of people.
Torwen:
Yeah, if there was a reason to, you could do it. In healthy people, I’ve seen TikToks from normal users wearing CGMs. And they share data and spread fear. They tell others not to eat certain carbs due to their graph. That’s not what I’d recommend it for.
Aidan:
Yeah, that kills me as well. Cool, we’ll wrap it up there. I think that shows our thoughts well. This has been episode 228 of the Ideal Nutrition Podcast. If you haven’t already, please leave a positive rating and review. We’d massively appreciate it.