CGMs are more convenient than finger prick tests. Photo: Unsplash
You might have seen your favourite wellness or fitness influencer lately sporting a small white spot on their upper arm. It’s a continuous glucose monitor (GGM) and it’s the latest biohacker ‘wearable’ for those keen on monitoring their every bodily function.
What is a continuous glucose monitor?
A continuous glucose monitor is a small device that measures blood sugar in real time via a tiny filament in the skin. It’s designed for use mainly by those with type 1 diabetes, but increasingly it’s being used in type 2 diabetes patients as well.
Specialist diabetes dietitian Kate Ellison, who works at Auckland’s Greenlane Diabetes Centre, says the devices help people with diabetes avoid dangerous low or high blood sugars.
“Traditionally people with diabetes have had a glucose monitor where they prick their finger and put a drop of blood on a little strip and the glucose monitor will give them a reading of blood sugar. Which is fine, but it's very burdensome for diabetes patients. And if a person is on insulin, they might have to do that 3, 4, 5 times a day.”
CGMs connect to a reader or an app on a smartphone, and mean people can do a lot less finger pricking.
“It will give them pretty much real time data on what their glucose levels are doing.”
Ellison says CGM devices measure interstitial glucose, which is “in the fluid between the cells, just underneath the skin. So, it's not strictly blood glucose that's being measured… and there is a bit of lag time between blood glucose and interstitial glucose.”
Patients can double-check any unusual readings by doing a finger-prick test.
In general, Ellison says, GGMs are “amazing, amazing technology for people with diabetes and it takes some of the burden away of living with diabetes… of having to think about it 24-7. It does allow people to have a better quality of life and make much more timely treatment decisions.”
It’s especially useful for children with diabetes and their parents, who can keep an eye on a child’s glucose levels while they’re at school, for example.
Why are people without diabetes using them?
It’s not clear how the trend of people without diabetes using CGMs began, but it may be down to makers of the devices seeing a way to expand their markets coinciding with the boom in ‘personalised wellness’.
In the US and increasingly in New Zealand, private clinics and expensive health retreats are promoting the devices as weight loss tools and as one website puts it, “a cutting-edge technology that can provide invaluable insights into your body’s response to different foods.”
The idea put forward by marketers is that by monitoring what you’re eating and what your blood sugar does in response, you can figure out what you should and should not be eating for optimal health.
Are there any benefits – and pitfalls?
CGMs are increasing being used as a wearable biohack. Photo: Unsplash
he use of CGMs in non-diabetic people has not been studied. So, we don’t really know if there are any benefits, despite what the promoters of GGMs might say. Benefits are anecdotal, at best.
There could be pitfalls, though.
“The difficulty is: how are people interpreting the data they're getting from a CGM if they don't have diabetes? Because as far as I'm aware, there are no real metrics that have been agreed by experts around the world or informed by large, well-controlled studies around what the results from a CGM in non-diabetics actually mean,” Ellison says.
An article published in the journal Practical Diabetes on this topic (subtitled: ‘an evidence-free zone’) documented people without diabetes being advised to track their blood glucose against diagnostic levels for diabetes or prediabetes. But these levels have no relevance for people who don’t have those conditions.
Ellison says it’s totally normal for blood glucose levels to rise after a meal.
“When people without diabetes eat carbohydrate, the blood glucose level will rise in response to that. That's very normal. And then the pancreas will release insulin to bring the blood glucose down back down to baseline levels within a few hours. That's normal.”
If you become aware of that rise because you’re using a CGM, she says, how is interpreted?
“What are they going to do with that data? Because effectively it means nothing. It means you've got a normal blood sugar. But what they're doing is interpreting rise and potentially changing something as a result.”
Blood glucose is also affected by lots of other factors unrelated to the meal you’ve just eaten – like the meal before that; stress levels; sleep and exercise.
The journal article says the risk with CGMs is users inadvertently making their health worse.
‘Based on the available evidence, the idea that CGMs allow people to determine the foods that they can and cannot tolerate is misleading and could result in – at best – unnecessary avoidance of foods.’
Ellison agrees.
“If you see your blood sugar rise and you say, oh, that shouldn't be happening – maybe I shouldn’t eat any carbohydrate food again… if people imagine that having a flat glucose line is what should be happening, that means they are going to be cutting out a lot of very normal and very healthy foods.”
There’s another potential risk: disordered eating.
“This could really feed into health anxiety and obsessiveness and hypervigilance around the misinterpretation of normal data as something to be concerned about. And I think that could possibly increase restrictive or disordered eating,” Ellison says.
What to do instead
If you’re worried, there’s a very well-researched blood test that most people should have regularly – every year or two – that’s used to screen for blood glucose trouble. It’s known as HbA1c, and it measures an average of blood glucose over the previous two to three months.
“That’s an excellent test that will show whether you have got slightly higher blood glucose, and whether we need to look into that further,” says Ellison.
Since a GGM can cost upwards of $90 per sensor – and you might need two or three in a month – an HbA1c test is not only more useful, but also a lot cheaper, too.
* Niki Bezzant is a writer, speaker, journalist and author focusing on health, wellbeing and science.