Science

What I Learned From Wearing a Blood Sugar Monitor

Once a tool for diabetics, CGMs are now being marketed to us all. Be skeptical.

A smoothie and two Cadbury Creme Eggs in front of a chart with a red line going up exponentially.
Photo illustration by Slate. Photos by Getty Images Plus and Amazon.

It’s refreshing to see that my biggest guilty pleasure, the Cadbury Creme Egg, isn’t so “bad” for me after all. Eating one makes my blood sugar spike only as much as drinking a fruit smoothie on an empty stomach. All that gooey, processed chocolate deliciousness is about as sugary as a banana with milk in a blender. Or—maybe it’s the smoothie that I should be looking at differently?

This observation is brought to me by a continuous glucose monitoring device, or CGM, a skin patch sensor that I’ve been wearing on my upper arm. The device monitors my blood sugar in real time using a tiny fiber penetrating slightly under my skin, alerting me to how “healthy”—or not—particular foods are.

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Since the late ’90s, CGMs have been used by people with diabetes to track their blood sugar. With diabetes, the pancreas has trouble breaking blood sugar down on its own, so it is necessary to keep careful watch over spikes and dips. But now, it seems blood sugar monitors are for everyone. A series of health-tech and wellness startup companies—such as Levels, NutriSense, January, Signos, or Veri—are trumpeting their manifold benefits for people whose pancreases are working just fine. There are even rumors that a future Apple Watch will include a glucose monitor.

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The claim behind widely deploying this tech: Keeping your blood sugar in check can do everything from fix your sleep to improve your mood, to lose weight, notably, all without demonizing certain foods outright or counting calories. “I think that everyone can benefit from understanding how food is directly affecting their health in real time,” Casey Means, co-founder of the metabolic health company Levels, tells Slate. “I see continuous glucose monitoring technology as a form of empowerment in the face of a very difficult health culture where many cards are stacked against us.”

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As a 25 year old who has a loose definition of what constitutes a “meal,” I was interested in what these devices could teach me about my body and how it responds to various foods. But I was also a little worried that wearing a CGM would make me hyperconscious about everything I’m eating—as well as skeptical of the lofty claims made by the companies that promote them.

To access the “empowerment” of a CGM, users must purchase the product, and then pay a monthly fee. For example, it currently costs $199 to sign up as a member to Levels, and then another $199 each month to have access to sensors for the CGM. Veri, the product I tested out, costs $169 for a monthlong subscription. Other brands fall into a similar price range. In the U.S., where CGMs require a prescription, the initial cost of the device includes an evaluation with a telehealth physician. In some cases, the apps also provide you with access to an expert to discuss your results for an additional fee.

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The Veri CGM comes with a sensor (Veri, as do most health-tech startups, uses the Abbott FreeStyle Libre sensor), an applicator, and a fabric adhesive patch to place over the sensor for protection. The app provided me with instructions for applying the product: pick the fattiest bit of your upper arm, disinfect it, use the applicator to stamp the sensor onto yourself (painless!), sync the sensor to your phone, and then wait a couple of hours for it to calibrate. It was a seamless process, and my sensor only felt weird some of the first nights while I was sleeping on it.

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The main purpose of the CGM is to tell you if and when your sugar spikes in response to something you eat. Blood sugar for a healthy person is usually between 70 and 110 mg/dL—that’s milligrams per deciliter—during fasting, and it can go up to 140 mg/dL in the 30 minutes or couple of hours after you’ve eaten, only to then go back down to resting range. For people with prediabetes, or diabetes, the fasting levels are higher: more than 100 and more than 126 mg/dL respectively. The apps that accompany the devices offer a suite of tools to interpret that raw information. The app I used, for example, had little emoji you could add onto the tracking dashboard to enforce the fact that changes in blood sugar correspond with meals and snacks. A little croissant for your first morning spike, a nice salad for that office lunch, and so forth. It also came with Instagram Story–like slides with nuggets of lessons on how sugar, stress, sleep, and exercise affect your blood sugar.

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I obsessed over my sugar intake the first couple of days of wearing the CGM—I dare anybody else not to. Strapping on a CGM is kind of like playing a video game, where your own body is the controller. Since the product gamifies eating, going as far as assigning scores to your meals, it would be easy to get caught up in wanting a perfect report card. (In particular, I bet these devices can be dangerous if you have an eating disorder, or you’re prone to disordered eating.)

After using a CGM for two weeks, I had learned a few useful things: going for a walk after a meal can curb the sugar spike, as does combining a sugary food with a fiber or a nonprocessed carb. For example, both that Creme Egg and that banana smoothie spiked my blood sugar a lot more when they were consumed alone, like as an afternoon snack, rather than as dessert after chicken and veggies. It’s very helpful to peer into your body and see a glimpse of its inner workings—it’s almost humbling to see on a graph what my body did with that cereal, that yogurt, that kebab, that soup, that sandwich.

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I found that my blood sugar stayed at an average of 80–90mg/dL between meals and peaked up to 125–135 mg/dL most of the times I ate, just to plummet back down a couple of hours after my meal. The app told me I needed to work on “staying in range” more, which basically means avoiding sugar peaks—but that didn’t come as news. I’ve long known I should start eating more regularly, since I have a bad habit of skipping lunches or not eating until my workday is over.

Anecdotally, keeping blood sugar stable can make you feel good and increase your performance, according to Means, the co-founder of Levels. The list of areas stable blood sugar can improve, per Means, is long and specific: mental acuity, athletic performance, cravings and hunger levels, sleep, and skin health. She points to Levels members who have benefited superlatively from the device: Betsy McLaughlin, who says she changed her diet and lost 81 pounds through glucose monitoring, and Halle Organ, who says she increased her energy levels with a CGM.

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I ran these claims by Viral Shah, a professor of medicine at the Barbara Davis Center for Diabetes. “Currently, it’s more marketing than science,” says Shah. “I think science-wise, it’s gonna take a really long time before we will discuss whether the CGMs should be used in healthy individuals.” With the exception of people who have diabetes, and those who are prediabetic, our bodies are pretty good at regulating glucose levels themselves. Shah is the lead author of a 2019 paper showing that, for healthy individuals, CGM results just don’t change that much regardless of behavior. In technical terms, levels stay between those 70 mg/dL and 140 mg/dL for 96 percent of the time.

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“If you look at our research, it’s boring. Like, your glucose remains within that really tight range throughout the day and night without much fluctuation—as expected because people have a normal, healthy pancreas,” Shah says. The only time my blood sugar spiked beyond the “healthy” range was, in fact, during an obviously unhealthy moment. I was stumbling around a shopping mall, dizzy and hungover from the previous night’s debauchery. I stopped at a café and inhaled a sugary lemonade with a side of ketoprofen for my headache. My blood sugar went from 58 mg/dL … to so high that the app wouldn’t even track it anymore. This, however, wasn’t catastrophic: The spike lasted for 15 minutes, and then we were back on track.

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No matter what you eat, no matter the alcohol, or the exercise, you basically still remain in a normal range, says Shah. What’s more, scientists still don’t currently know what kind of fluctuations in glucose levels in healthy people are optimal, though there are some studies underway trying to establish this. Shah is open to the idea that further research could suggest a clear reason for the average person to use a CGM. “Maybe over a couple of years when we will have more data, our opinion will change,” he explains.

In the meantime, perhaps a CGM could be a motivator for eating healthy—seeing a spike in response to a lemonade could help you internalize that it’s super sugary—though it’s hardly going to do the difficult work of doing healthy grocery shopping and sticking to a healthy diet. “This is going to be another tool that the more affluent, fortunate people get to use,” says Jane Burrell, a clinical nutrition professor at Syracuse University. She sees the target audience as young professionals with money to spend, or middle-aged people starting to think more critically about their health (people who are also likely to have access to nutrient dense foods already). “Do they need it? I don’t know. Some may benefit from it, some people get really into it and so it’s just another tool, right?” says Burrell.

After two weeks with the CGM, I was personally ready to take the device off and stop looking for a deeper meaning or a “healthier” me in the foods I was eating. It was a little bit of relief not to have an app instantly trying to make sense of my meals and snacks. Without the careful watch of an app, eating that Creme Egg or fruit smoothie isn’t necessarily “bad.” It just is.

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