Measure blood sugar with a grain of salt

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Continuous glucose monitors (CGMs), once limited to diabetes care, are now being explored by healthy individuals and researchers alike. But as science reveals, interpreting their data in people without diabetes is far from straightforward
Credits: Unsplash

Nicole Spartano doesn’t have diabetes. Yet the Boston University epidemiologist has worn a continuous glucose monitor (CGM) from time to time. Her interest is personal and professional: she wants to understand how food, sleep, and exercise affect her blood sugar, and whether these devices could help people prevent diseases like diabetes while also improving overall health.

CGMs were originally developed for people with diabetes to track blood sugar and guide insulin use. Insulin is the hormone that allows cells to absorb glucose and convert it into energy. But in people without diabetes, what CGM readings mean is still an open question.

Despite that uncertainty, CGMs have surged in popularity. High-profile figures such as Casey Means — who cofounded a company selling the devices and wrote the 2024 book Good Energy — have promoted them as tools to combat what she calls the “Bad Energy crisis” in Western lifestyles. In 2024, the U.S. Food and Drug Administration made CGMs available without a prescription. Today, a two-week sensor costs about $50.

The devices are small patches worn on the arm or abdomen, with a hair-thin needle that sits in the interstitial fluid beneath the skin. They measure glucose that diffuses into that fluid and send updates every few minutes to a smartphone. Conventional blood tests suggest that 70–140 milligrams per deciliter (mg/dL) is an optimal range when not fasting. Spending too much time above that range has been linked to cardiovascular risks, fatigue, and anxiety.

Endocrinologist Ruchi Mathur at Cedars-Sinai explains that CGMs may help people design personalized diets. Responses to food differ widely — even the same sandwich on different types of bread can create very different blood sugar curves. But the interpretation is tricky. A study in The American Journal of Clinical Nutrition (Hengist et al., 2025) showed that the same person’s glucose response to an identical meal can vary from week to week. Spartano’s own research found that people without diabetes spend about three hours a day above 140 mg/dL — raising questions about whether current definitions of “normal” even apply.

Clinicians are cautious. When Spartano shared complex CGM results with doctors, they rarely agreed on whether follow-up testing was needed. “We want to be able to tell people, ‘This looks normal, this looks abnormal.’ But we don’t really know what normal is,” she says.

Vijaya Surampudi, an endocrinologist at UCLA, agrees. There is no standard way to interpret CGM data in healthy people. That’s why she encourages patients to record meals, stress, exercise, and sleep alongside glucose trends — context matters as much as the numbers themselves.

And numbers can be misleading. Spartano recalls scarfing rice quickly, which kept her glucose flat, while eating it slowly caused a spike. Taken at face value, she might have concluded that eating as fast as possible was “healthier.” But of course, wolfing down food encourages overeating and reduces nutrient absorption. “Blood sugar shouldn’t be all we focus on,” she emphasizes.

For now, CGMs in people without diabetes remain an experiment. They may offer useful insights — but the science is still catching up.

References

A. Hengist et al. Imprecision nutrition? Intraindividual variability of glucose responses to duplicate presented meals in adults without diabetes. The American Journal of Clinical Nutrition, Vol. 121, January 2025, p.74, doi:10.1016/j.ajcnut.2024.10.007

N.L. Spartano et al. Expert clinical interpretation of continuous glucose monitor reports from individuals without diabetes. Journal of Diabetes Science and Technology, Posted Feb. 12, 2025, doi:10.1177/19322968251315171

N.L. Spartano et al. Defining continuous glucose monitor time in range in a large, community-based cohort without diabetes. The Journal of Clinical Endocrinology & Metabolism, Vol. 110, April 2025, p.1,128, doi: 10.1210/clinem/dgae626

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