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Continuous glucose monitors (CGMs) are having a moment.

Previously worn primarily by people with diabetes to help keep tabs on their blood sugar, health and fitness enthusiasts who don’t have diabetes are now also growing users of CGMs.

People think CGMs are helpful based on two findings:

1. Extreme post-meal blood-sugar spikes are linked to a variety of health problems. (1)

2. Two different people might have very different blood-sugar responses to the same meal. (2)

Theoretically, wearing a CGM can reveal if someone’s blood sugar is swinging wildly, and whether certain foods are especially likely to cause blood sugar spikes for them.

Past research has shown that for people who don’t have diabetes, CGMs might not be all that useful. (3)

That’s because a person’s response to a given food can vary from one day to the next, or even at different times within the same day. A person’s response to a food can fluctuate because of physiological factors (brought on by acute stress, sleep deprivation, or changing activity levels), or just because the CGM device isn’t reliable.

One area where CGMs show more promise: Identifying pre-diabetes and diabetes before a typical blood test would.

And that’s exactly the focus of a new study published in Nature Medicine. (4)

How the study worked

Researchers had over 8,000 people (ages 40 to 70) who hadn’t been diagnosed with diabetes wear a CGM for two weeks.

The goal: To see if wearing a CGM could help sniff out pre-diabetes or diabetes more accurately than a typical blood test.

A typical blood test uses just one sample to decide whether someone’s fasting blood glucose is in a normal range.

Meanwhile, a CGM can easily measure fasting blood sugar multiple times over a longer period of time, providing more data points.

That could potentially mean a more accurate and nuanced picture of someone’s typical fasting blood sugar.

What the study found

Based on the first CGM reading, around 64 percent of participants had normal fasting blood sugar.

But when all the measurements taken over the course of the study were taken into account, the picture looked different:

• About 50 percent of the entire group was classified as having pre-diabetes.

• 40 percent of the group who initially had a normal reading were re-classified as having pre-diabetes.

• Among those in the group with an initial normal reading, 2 percent were re-classified as having suspected diabetes, and 1 percent with diagnosed diabetes.

Takeaways

1. CGMs have their flaws, but they can be useful—especially for early detection of prediabetes and diabetes.

Last time we covered CGMs, we emphasized their limitations—which still apply.

For instance, fluctuations in blood sugar response are normal—and dependent on lots of factors (for example, stress levels, what else you’ve eaten, if / how you’ve exercised that day).

So, for people without diabetes, a CGM is best used as a data-gathering, hypothesis-generating device—rather than a foolproof way to assess how individual foods affect you.

At the same time, this study shows that using a CGM could give you information that’s worth following up with your doctor about. Which brings us to…

2. A doctor can help with weird or inconsistent results.

If you notice that your CGM readings are all over the place either before meals or after, it’s definitely worth a chat with a doctor. (Of course, this conversation should include talking about things like diet, but also about things like stress levels, activity levels, and sleep quality, all of which can affect blood sugar regulation.)

A medical doctor can examine the results, consider them in the context of your lifestyle, decide if any more tests would be helpful, and plan the next steps.

I’ve had a few clients come through and experiment with CGMs. None of them have diabetes or learned of prediabetes from their experience, but they did learn how certain foods affect their blood sugar, how much exercise they need to lower their levels if they spike, and the glycemic index of foods. When you discover so many nuances about yourself, it’s hard not to chalk that learning up as a ‘W.’

To your health,

Michael Beiter

Certified Personal Trainer

PN L1 Sleep, Stress Management, and Recovery coach

References

1. Blaak EE, Antoine JM, Benton D, Björck I, Bozzetto L, Brouns F, et al. Impact of postprandial glycaemia on health and prevention of disease. Obes Rev. 2012 Oct;13(10):923–84.

2. Zeevi D, Korem T, Zmora N, Israeli D, Rothschild D, Weinberger A, et al. Personalized Nutrition by Prediction of Glycemic Responses. Cell. 2015 Nov 19;163(5):1079–94.

3. Hengist A, Guo J, Hall KD. Imprecision nutrition? Duplicate meals result in unreliable individual glycemic responses measured by continuous glucose monitors across three dietary patterns in adults without diabetes. bioRxiv. 2023.

4. Shilo S, Ayya Keshet, Rossman H, Godneva A, Yeela Talmor-Barkan, Aviv Y, et al. Continuous glucose monitoring and intrapersonal variability in fasting glucose. Nature medicine. 2024 Apr 8.