Glucose sensors catch every spike, and in healthy people most spikes are normal

Key takeaways

• The FDA cleared the first over-the-counter glucose sensor in March 2024, and in June 2026 it cleared one for children as young as 2 who don’t use insulin.
• In a 2019 study of 153 healthy people, the typical participant’s sensor showed blood sugar above 140 for about 30 minutes a day, so short spikes after meals are normal.
• A small 2025 trial found that a sensor overestimated glucose in people without diabetes, showing about four times more time out of range than fingerstick tests.
• For people who use insulin, these sensors are a proven tool. For people without diabetes, a 2024 review found no consistent, high-quality evidence of health benefits.
• If you have a history of disordered eating, the FDA says to talk with a health care provider before you use one.

In 2018, Stanford researchers asked adults to eat a bowl of cornflakes with milk while a sensor tracked their blood sugar. In about 80% of the people tested, glucose climbed above 140 milligrams per deciliter (mg/dL)⁷.

None had been diagnosed with diabetes before the study, though screening found prediabetes or diabetes in some of them⁷. For comparison, a healthy person’s blood sugar is 140 or lower two hours into a standard lab glucose test⁸.

You can now run the same experiment on your own arm. Since March 2024, adults have been able to buy a continuous glucose monitor (CGM) without a prescription. In June 2026, the Food and Drug Administration (FDA) cleared one for children as young as 2¹².

For people with diabetes, especially those who take insulin, a CGM can be a major help⁴. For people without diabetes, the picture is murkier. Normal rises look alarming on a graph, readings may run high, and there’s little good evidence that watching your glucose improves health⁵⁹.

This guide covers what the sensor measures, what normal looks like, who benefits, the risks, and a two-week plan for trying one.

What you’re buying: a sensor in the fluid under your skin

A CGM has a small sensor that sits under the skin, usually on the belly or arm. It measures glucose in the fluid between your cells, not in your blood, and estimates your level every few minutes⁴. Disposable sensors last about one to two weeks, depending on the model¹⁴.

That fluid trails your blood. By the estimate of Adam Collins, a nutrition researcher at the University of Surrey, the gap runs anywhere from several minutes to roughly 30⁵. It matters most when glucose is moving quickly, as it does soon after you eat.

Three over-the-counter devices arrived in 2024:

• Dexcom Stelo, cleared March 5, 2024, for adults who don’t use insulin. That includes people without diabetes who want to see how food and exercise affect their glucose. Each sensor lasts up to 15 days, and the app shows readings every 15 minutes¹.
• Abbott Lingo, cleared June 10, 2024, is a 14-day wellness sensor for adults not on insulin. Abbott says it is not meant to diagnose any disease, including diabetes³.
• Abbott libre Rio, cleared the same day, is for adults with type 2 diabetes who don’t use insulin. Abbott says it reads from 40 to 400 mg/dL³.

On June 12, 2026, the FDA extended Stelo to children 2 and older who don’t use insulin, under an adult’s supervision².

The fine print matters. These sensors are not for people who use insulin. They are also not for people with problem lows, because they aren’t designed to warn you when your blood sugar drops dangerously¹. The FDA also says not to make medical decisions from the readings without talking with your provider¹.

Healthy blood sugar rises after meals: how much

The best picture of normal comes from a 2019 study led by Viral Shah. His team recruited 153 healthy, non-obese volunteers, from age 7 to 80, through 12 clinics in the T1D Exchange network. Each wore a sensor for as long as 10 days, blinded so they couldn’t watch their own numbers⁶.

In most age groups, average glucose sat at 98 to 99 mg/dL; only the over-60 group ran a bit higher, at 104⁶. The typical volunteer stayed between 70 and 140 for 96% of the day⁶.

This is the surprise. The typical participant spent about 30 minutes a day above 140 and about 15 minutes a day below 70⁶. Those are healthy people having ordinary days.

The Stanford study showed that the meal matters. Cornflakes with milk, a low-fiber, high-sugar breakfast, caused the biggest rises. Bread with peanut butter, which adds fiber, fat and protein, produced gentler responses in more people⁷.

Lab tests, not sensors, are what doctors use to diagnose. The Centers for Disease Control and Prevention (CDC) says a fasting blood sugar of 99 or lower is normal, 100 to 125 suggests prediabetes, and 126 or higher suggests diabetes⁸.

What you see on the app	What it likely means	What to do
A rise above 140 for less than an hour after a starchy or sweet meal	Common in healthy people67	Note the meal. No action needed
Most of the day between 70 and 140	The usual healthy pattern6	Nothing
A brief dip into the 60s and you feel fine	Healthy people spent about 15 minutes a day under 706	Recheck with a fingerstick meter if it worries you
Morning readings repeatedly at 100 or higher	Could hint at prediabetes, but a sensor can’t diagnose it810	Ask your clinician for a lab test
Frequent readings above 200, or thirst and frequent urination	Possible diabetes815	Call your clinician soon

In people without diabetes, sensors can run high and disagree

Most CGMs were designed for people with diabetes. Sufyan Hussain, a diabetes physician at King’s College London who has done advisory work for Abbott UK, warns that the numbers can be shakier in healthy people, above all when a device wasn’t built or tuned for the narrower range a healthy body stays in⁵.

In February 2025, the American Journal of Clinical Nutrition published a randomized crossover trial of 15 healthy adults. In a crossover trial, every person tries each test condition in a random order. After standard meals, the sensor read higher than fingerstick tests. It counted about four times as much time out of range, and how much it overshot varied by meal and by person⁵.

It was a small study, and Hussain noted that it compared sensors with home meters rather than lab tests⁵. Still, it points to a real limit.

A 2024 review in the journal Diabetic Medicine cites another study in which people without diabetes wore different sensors at the same time. The devices ranked the same meals differently⁹. If sensors on the same body can’t agree on which meal was gentler, small differences between foods probably don’t mean much.

Experts struggle too. Nicole Spartano’s team at Boston University showed 20 hard-to-read sensor printouts from people without diabetes to clinicians who treat complex diabetes. Their readings of the data, and their advice on follow-up, were all over the map¹⁰.

For diabetes, a CGM is a proven tool, and the circle is widening

For people who need insulin, CGMs are a recommended part of care. The National Institutes of Health (NIH) says those who wear one every day or nearly every day benefit most⁴.

The American Diabetes Association (ADA) widened its advice in its Standards of Care for 2026, released in December 2025. It now recommends CGMs from the time diabetes is diagnosed, or any time after, for people who may benefit. That advice is no longer limited to insulin users or people at high risk of lows¹².

New trial data support that shift. In the CONNECT trial, presented at the ADA’s June 2026 meeting, 283 adults with type 2 diabetes who didn’t use insulin were randomly assigned to a CGM or to usual fingerstick testing at 22 primary care practices¹³.

After 26 weeks, A1C, a blood test that reflects average glucose, fell 0.9 points more in the CGM group. That group also spent five more hours a day in the target range¹³. Participants started with an average A1C of 8.8%¹³. The results were presented at a meeting, and the press release didn’t name the funder.

If you have diabetes, a CGM is worth discussing with your clinician. Prescription sensors may be covered; the NIH suggests checking with your plan or Medicare⁴.

For everyone else, the payoff hasn’t been shown

People without diabetes buy sensors for three hopes: to catch problems early, to change their habits and to improve their metabolism. The 2024 Diabetic Medicine review examined all three. It found “a lack of consistent and high-quality evidence” for any of them⁹.

Real-world records point the same way. Epic Research, the research arm of a large health records company, studied 9,675 adults without diabetes whose A1C was 5.0% to 5.9%. Over 6 to 18 months, average A1C barely moved whether they were prescribed a CGM, test strips or nothing at all. The CGM group’s average rose by 0.02 points¹¹.

That analysis was observational, counted prescriptions rather than actual use, and was posted by Epic rather than in a journal¹¹. It can’t prove sensors help no one, but it found no sign of a broad benefit.

Early detection is the most intriguing idea. In the Stanford study, about a quarter of people with normal standard tests showed large, frequent swings⁷. Nine of the 23 people in the most variable group would not have been diagnosed with prediabetes or diabetes by standard tests⁷.

The study was small and short, though, and it didn’t follow anyone over time. No one yet knows whether those swings predict disease⁷. Spartano notes that CGMs are not approved to diagnose or predict prediabetes or diabetes¹⁰.

Why the same food spikes one person and not another, and whether apps can turn that into a diet plan, is covered in our companion article on personalized nutrition algorithms.

The risks: food fear, skin trouble and missed lows

The most serious risk is to your relationship with food. A graph that turns red after a banana can make an ordinary meal feel like a mistake.

The FDA’s 2026 announcement says people with a history of disordered eating or eating disorders should talk with a health care provider before using the device². Abbott gives the same advice for Lingo³. The 2024 review notes that possible harms, including obsessive tracking and orthorexia, an unhealthy fixation on eating “correctly,” have barely been studied⁹.

Other risks are more physical:

• Skin. In Stelo’s study, users reported local infections, skin irritation, and pain or discomfort¹. The adhesive can also cause redness⁴.
• Missed lows. Over-the-counter sensors aren’t built to warn of dangerous lows¹. If you have symptoms, treat the symptoms, not the app.
• False reassurance. A calm graph doesn’t rule out other problems. A sensor is not a checkup.
• Marketing that outruns the evidence. Abbott says Lingo can help people “retrain their metabolism”³. The review’s authors argue that claims of benefit for people without diabetes should be labeled misleading⁹.

A two-week experiment that keeps the sensor in its place

If you want to try a sensor, treat it as a short experiment with a clear question, not a permanent scoreboard. This plan is ours, not a tested protocol.

1. Write down one question. For example: “Does my usual breakfast keep me steady through the morning?”
2. Spend week one observing. Eat as you normally do. Log meals, sleep, exercise and stress, and change nothing.
3. Read in hours, not points. Look at how long you stay above about 140 and whether you return to your usual range. Ignore a few points of difference; sensors can overshoot⁵.
4. In week two, change one thing at a time. For example, swap a low-fiber cereal for a breakfast with more fiber, fat and protein, as in the Stanford meals⁷.
5. Check surprises. Confirm a reading that doesn’t match how you feel with a fingerstick meter⁴.
6. Turn the data into a question for your clinician. A pattern of high morning readings is a reason to ask for an A1C or a fasting lab test⁸.
7. Stop if it makes eating stressful. The data aren’t worth your peace at the table.

Natural health has long taught people to notice how food makes them feel: energized, sluggish, satisfied or hungry an hour later. A sensor can put numbers on that awareness, and the Stanford results fit a familiar idea. In those test meals, the breakfast with more fiber, fat and protein landed more gently than the sugary, refined cereal⁷.

But your body’s signals still come first. A rise after a meal is part of how you process food, not a grade on your character.

What the evidence supports

Claim	Evidence level	What the research shows
CGMs help people who use insulin manage diabetes	Strong evidence	Recommended by the NIH and the ADA412
CGMs help people with type 2 diabetes who don’t use insulin	Promising but early	ADA widened its advice; a 2026 trial, so far reported only at a meeting, cut A1C 0.9 points more than usual care1213
Short spikes above 140 after meals mean something is wrong	Evidence says no, or unsafe	Healthy people spend about 30 minutes a day above 14067
Sensor readings in healthy people are precise enough to rank foods	Evidence says no, or unsafe	One sensor overestimated; two sensors disagreed on meal rankings59
Wearing a CGM improves health in people without diabetes	Not enough evidence	No consistent trials; A1C unchanged in health records911
CGM patterns can spot early blood sugar problems	Promising but early	Small, short study with no long-term follow-up710
CGMs can harm some people’s relationship with food	Not enough evidence	Little studied; the FDA advises caution29

When a reading or a symptom means call your clinician

Symptoms outrank the screen. A sensor can lag, overshoot or miss a low, so act on how you feel.

What you notice	What to do
Shaking, sweating, confusion or dizziness, whatever the app shows	These can be signs of low blood sugar, and sensors may miss lows. Get help, especially if symptoms are severe114
Repeated low readings or symptoms without diabetes	See your provider to find the cause. Without diabetes, true lows are usually below 5514
Intense thirst, dry mouth, blurred vision, fatigue or frequent urination	Call your provider. These can be signs of high blood sugar15
Blood sugar too high or too low and you don’t know why	Contact your provider15
Morning readings often at 100 or more	Ask for an A1C or fasting lab test8
Redness, swelling, warmth or pain at the sensor site	Call your provider. Skin infections were reported in testing1

You can report a device problem, such as a skin infection or a sensor that fails, to the FDA’s MedWatch program.

Questions readers ask

The bottom line

Over-the-counter glucose sensors give anyone a live view of blood sugar. For people who use insulin, and increasingly for others with diabetes, that view helps. For people without diabetes, short spikes after meals are normal, readings can run high, and the health benefits remain unproven.

If you’re curious, run a short, focused experiment, read patterns rather than single numbers, and let symptoms and lab tests, not the app, decide when you need care.

Keep exploring: wearable accuracy and interpreting wearable data.

Related reading

• Your response to food is personal, but the payoff from diet algorithms is modest
• “FDA registered” isn’t “FDA approved”: a buyer’s map to wellness devices
• Why being out of range often means nothing at all
• Your wearable’s best number is your own normal, not the average
• Your wearable gets resting pulse right, while calories and sleep are another story

Sources

1. U.S. Food and Drug Administration. “FDA Clears First Over-the-Counter Continuous Glucose Monitor.” FDA news release, March 5, 2024. fda.gov
2. U.S. Food and Drug Administration. “FDA Clears First Over-the-Counter Continuous Glucose Monitor for Children.” FDA news release, June 12, 2026. fda.gov
3. Abbott. “Abbott Receives U.S. FDA Clearance for Two New Over-the-Counter Continuous Glucose Monitoring Systems.” Company press release, June 10, 2024 (cited for clearance facts and company claims). abbott.mediaroom.com
4. National Institute of Diabetes and Digestive and Kidney Diseases. “Continuous Glucose Monitoring.” NIH, last reviewed June 2023. niddk.nih.gov
5. Science Media Centre. “Expert reaction to study looking at continuous glucose monitors and measuring blood sugar levels in people without diabetes” (on Hutchins KM, et al., American Journal of Clinical Nutrition, 2025). February 26, 2025. sciencemediacentre.org
6. Shah VN, DuBose SN, Li Z, Beck RW, et al. “Continuous Glucose Monitoring Profiles in Healthy Non-Diabetic Participants: A Multicenter Prospective Study.” Journal of Clinical Endocrinology and Metabolism, 2019. scholarlycommons.henryford.com
7. Hall H, Perelman D, Breschi A, et al. “Glucotypes reveal new patterns of glucose dysregulation.” PLOS Biology, 2018. journals.plos.org
8. Centers for Disease Control and Prevention. “Diabetes Testing.” CDC, May 15, 2024. cdc.gov
9. Oganesova Z, Pemberton J, Brown A. “Innovative solution or cause for concern? The use of continuous glucose monitors in people not living with diabetes: A narrative review.” Diabetic Medicine, 2024. discovery-pp.ucl.ac.uk (preprint with references: preprints.org)
10. Boston University Chobanian & Avedisian School of Medicine. “Guidelines Needed for Interpreting Continuous Glucose Monitoring Reports in those Without Diabetes.” BU news release (on Spartano N, et al., Journal of Diabetes Science and Technology).
11. Epic Research (Bartelt K, Barkley E, Wong K, Deckert J). “Continuous, Intermittent, and No Glucose Monitoring All Associated With Negligible Changes in Average Blood Glucose Among Nondiabetic Adults After 6 to 18 Months.” Epic Research, updated August 6, 2025. media.epic.com
12. Patient Care Online. “ADA Publishes 2026 Standards of Care With Updates to Sections on Technology, Obesity, Cardiometabolic Disease Management.” December 9, 2025. patientcareonline.com
13. American Diabetes Association. Press release on the CONNECT trial, presented at the 2026 Scientific Sessions, June 6, 2026. professional.diabetes.org
14. MedlinePlus. “Hypoglycemia.” National Library of Medicine, updated April 17, 2023. medlineplus.gov
15. MedlinePlus. “High blood sugar – self-care.” National Library of Medicine, reviewed January 25, 2026. medlineplus.gov