Should you track your blood sugar with a continuous glucose monitor?
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The device itself is small, but the hype around it is big
Continuous glucose monitors are only about the size of aquarter, but the companies that sell them make huge claims about their health benefits: You can “revolutionize your health,” one company says
President Trump’s nominee for surgeon general, Dr. Casey Means, is a prominent proponent of continuous glucose monitoring. She co-founded a company that distributes the devices and sells an app to help people use them
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The monitor is a painless patch that inserts a needle into your skin. Every few minutes or so, it sends a signal to an app on your phone with an estimate of your blood sugar. (It measures the sugar concentration between your skin cells, which roughly correlates with your blood sugar level.) The app also helps you keep a log of everything you eat, so that you can track how different foods impact your blood sugar.
Studies have found that this technology has transformed care for people with diabetes. “It has revolutionized their and their families’ lives,” says Elizabeth Selvin, who researches diabetes at Johns Hopkins University
But in March 2024, the Food and Drug Administration approved the first continuous glucose monitors for people without diabetes. Currently, two companies are making them: Dexcom and Abbott. Each patch lasts about two weeks and costs about $50, so tracking your blood sugar for an extended period of time costs about $100 each month
The critical question is: Do they actually help people without diabetes or prediabetes improve their health?
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The theory
After you eat a meal that contains carbohydrates, a healthy person’s blood sugar rises, peaks and then gently falls back to baseline
“These peaks and troughs are the normal physiological response to consuming carbohydrates, in people without diabetes,” says nutritionist Sarah Berry, a professor of nutrition at King’s College London. Berry is also chief scientist at Zoe, a company that distributes continuous glucose monitors (CGMs) and an app to interpret the data. “We do not need to flatten these curves,” she says
But problems can arise when these peaks become too frequent and too high, Berry says. That could put you at a higher risk of obesity, cancer, cardiovascular disease and Type 2 diabetes, studies show. It can also make you hungrier between meals, Berry says, so you’ll eat more at the next meal
The idea behind glucose monitoring is that it could help you identify specific meals or meal sizes that produce extreme peaks. Then if you modify the meal, that shift could help you lose weight, reduce your risk of diabetes or simply help you feel better
The findings
Two major studies have tested this theory with randomized control trials. In the studies, people wore a glucose monitoring patch for a period of time while they tracked what they ate on an app. Researchers used the data to design a personalized diet aimed at lowering blood sugar. Then the scientists tested how well this CGM-based diet stacked up against a standard low-fat or Mediterranean diet
At a population level, the findings have been mixed. In one study at the Weizmann Institute of Science, the CGM-based diet didn’t help people lose more weight than simply following the Mediterranean diet. However, it did help them lower their blood sugar more, scientists reported in the journal Diabetes Care
The second study compared the CGM-based diet to a low-fat, high-whole-grain diet. On average, both diets led to the same amount of weight loss and small improvements in blood sugar, researchers at New York University reported in the journal JAMA Network Open and The American Journal of Clinical Nutrition. But Collin Popp, who helped lead this study, said the overall findings don’t tell the whole story. These conclusions show only the average response across the whole population, Popp says.
“When you look at the individual level, it’s very different,” he says. For some people, the glucose-monitoring approach helped tremendously. Some people lost a large amount of weight. “We had individuals coming back and saying, ‘You changed my life. I lost 30 pounds and I feel great.’ Other people in the study put on weight.”
So now scientists are trying to figure out who benefits from this technology
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When glucose monitors might be useful
1. If you’re highly sensitive to carbohydrates
Nutritionist Karen Kennedy has been helping people interpret and understand their glucose-monitoring data for five years. In her experience, these devices help some people discover a heightened sensitivity to carbohydrates, even to healthy versions, such as whole grains
“They eat brown rice, quinoa, beans, rice or oatmeal, and their blood glucose consistently goes really high,” she says
The monitor helps them realize that they’ll manage their blood sugar better on a low-carb diet. “Not zero carbohydrates, but lower carbohydrates,” Kennedy says
“They change their diets, and then their blood sugar comes down dramatically,” Kennedy says. “If they can keep up that new diet, they feel better and lose visceral fat.”
2. If you need extra motivation to eat healthier foods
Many people already know what they need to do to improve their metabolic health. But putting this advice into practice — that’s hard, both Kennedy and NYU’s Popp say
The quick feedback from a continuous glucose monitor may give them a nudge to actually implement nutritional advice. “It’s a motivator,” Popp says
For example, one of Kennedy’s clients clearly needed to add more protein and fat to their breakfast
“They were like, ‘Sorry, but this is my breakfast, and it has worked for me for 30 years.'”
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Then the client wore a patch for a week and saw how that breakfast shot their blood sugar super-high. They immediately changed their breakfast, Kennedy says. Right away, the client could see how this new breakfast improved their blood sugar levels
“They didn’t have to wait a few months and go to the doctor to see it working,” she says. “That agency can be motivating.”
3. If you need more awareness about your diet
In the study at NYU, some people greatly benefited from the CGM-based diet. When Popp and his colleague dug into their data deeper, they found one key factor for this success: whether the person consistently logged their meals into the device’s app over the six-month experiment
For some people, simply documenting what they ate helped them improve their diet and their blood sugar levels, Popp says. “I tell people all the time, ‘Monitoring what you do can play a huge role in your health.’
“And you don’t need to log the food accurately,” he adds. “It’s the mere act of documenting it that’s important for most people.”
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“We know that awareness helps people lose weight,” adds Johns Hopkins’ Selvin. “And it doesn’t have to be with an app. I have a colleague who uses a little pocket notepad. It adds accountability” — and it’s cheaper than glucose monitoring
Before you decide to buy the device, experts say, be aware:
Many people find the data confusing and unhelpful.
“Many people come to me and say, ‘I have been using the device for three or even 12 months, and I have all this data, but I don’t know what it means. I don’t know how to lower my blood sugar or improve it,'” Kennedy says
People really need to be educated about what the data means, Popp agrees. But that education will go only so far because at this point, some of the data is still mysterious to scientists and doctors
If you’re staying within a normal range, say about 70 mg/dL to 140 mg/dL, scientists still don’t understand what the peaks and troughs mean
“There’s no real standard guidelines about what’s a good peak or a bad peak in nondiabetics,” Popp says
The data can be misleading. First off, the devices aren’t super precise or accurate, and our bodies don’t always respond the same way to the same food. One recent study in The American Journal of Clinical Nutritionfound that the same meal on two different days gave very different readings. Another small study, in the same journal, found that the continuous glucose monitor overestimated people’s blood sugar levels compared with directly measuring it in the blood.
Second, the data can make people worry about — or even stop — eating healthy foods that cause normal blood sugar fluctuations. For example, Popp has a friend who started to worry about blueberries because they made her blood sugar rise slightly and then decline
“You don’t want to start tagging foods as ‘unhealthy’ just because it led to what I perceived as a minuscule blood sugar spike.”
Third, some people can have what looks like normal blood sugar levels but still have insulin resistance, Kennedy explains. In this case, their bodies compensate by overproducing insulin. To figure this out, you would need to see a doctor and have your insulin levels checked
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“Continuous glucose is a handy metric,” she says. “But it’s only one metric, and you have to use it in the context of lab results and other signs and symptoms.”
Edited by Jane Greenhalgh
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