Evidence explainerMetabolic Health & Blood Sugar

What CGM Readings Mean Without Diabetes: Normal Ranges, Spikes and the Limits of the Data

In healthy people without diabetes wearing a CGM, glucose sat between 70 and 140 mg/dL about 96% of the day. Two sensors worn at once ranked the same meals differently, and a CGM’s estimated A1C ran high in people without diabetes.

By Kymata Labs EditorialPublished October 11, 2026Last verified October 11, 2026

Medical review pending. Written by our editorial team from the studies and documents cited below; a credentialed clinician has not reviewed it yet. Educational only, not medical advice.

Key takeaways

  • FDA cleared Dexcom Stelo (March 5, 2024) and Abbott Lingo (May 29, 2024) for over-the-counter use by adults 18 and older who are not on insulin [1][2].
  • Neither is built to warn about lows: Stelo is not for people with problematic hypoglycemia, and Lingo has no glucose alarms and shows readings from 55 to 200 mg/dL [1][2].
  • In 153 healthy people without diabetes, average sensor glucose was 98 to 99 mg/dL (104 mg/dL over age 60), with a median 96% of the day between 70 and 140 mg/dL and about 30 minutes a day above 140 [3].
  • Two different CGMs worn at the same time ranked the same meals inconsistently in 16 adults without diabetes (rank correlation 0.43) [6].
  • In people without diabetes, the CGM-based glucose management indicator averaged 0.59 points higher than lab HbA1c [7].

The two over-the-counter CGMs

Stelo is cleared for adults 18 and older not on insulin, including people with diabetes on oral medicines and people without diabetes; it shows readings every 15 minutes, each sensor lasts up to 15 days, and reported adverse events included local infection, skin irritation and discomfort [1].

Lingo is built on the FreeStyle Libre 2 sensor, is worn on the back of the upper arm for up to 14 days, and is cleared to help detect normal and abnormal glucose levels and show how diet and exercise affect glucose; it displays 55 to 200 mg/dL and has no alarms [2]. Both clearances state that users should not take medical action based on the readings without a health care professional [1][2].

What normal looks like

A multicenter study fitted 153 healthy, non-obese people aged 7 to 80 with blinded Dexcom G6 sensors for up to 10 days. Mean glucose was 98 to 99 mg/dL in every age group except over-60s (104 mg/dL); the median time between 70 and 140 mg/dL was 96%, time above 140 was 2.1% (about 30 minutes a day) and time below 70 was 1.1% (about 15 minutes a day) [3].

Glucose varied by about 17% within each person over the day [3], so short excursions above 140 or dips below 70 were part of normal readings in this group.

Spikes in people with normal lab tests

A 2018 study found that even people classed as normoglycemic by standard tests reached glucose in the prediabetic range 15% of the time and the diabetic range 2% of the time on CGM, and that responses to identical meals varied widely between people [4].

In a 2015 study of 800 people and 46,898 meals, glucose responses to the same foods varied widely; an algorithm using blood tests, diet, activity and gut bacteria predicted personal responses and was validated in 100 more people [5]. These studies describe variability; they did not show that the spikes themselves cause disease.

What CGM data cannot tell you

When 16 adults without diabetes wore a Dexcom and an Abbott sensor at the same time, the two devices often disagreed about which meals caused bigger rises (rank correlation 0.43), and choosing meals by one device lost about half the glucose benefit measured by the other [6].

The glucose management indicator, a formula that estimates A1C from sensor averages, ran 0.59 points above lab HbA1c on average in people without diabetes, and differed by 0.4 points or more in 71% of them [7]. A CGM estimate is not a substitute for a lab A1C.

Does wearing one improve health?

The studies above describe normal readings, variability and device agreement; none tested whether acting on CGM data improves long-term health [3][4][6]. Our CGM without diabetes guide covers the trial evidence on diet and activity changes, and our prediabetes guide covers what has been shown to prevent diabetes.

Partners we link to

  • SignosPaid linkA continuous glucose monitor program: Dexcom’s over-the-counter Stelo sensor (two 15-day sensors a month), the Signos app and in-app dietitian chat. FDA-cleared for adults 18 and older who are not on insulin; Signos says not to change medication based on readings without your clinician. List price $169/mo on the 6-month plan (Oct 11, 2026); Signos was showing a 25%-off promotion that day. All sales final.See Signos CGM plans (opens in new tab)

    Partner links may earn us a commission. Learn more

Quick answers

Is a reading above 140 mg/dL after a meal abnormal?

Healthy people in the reference study spent a median of about 30 minutes a day above 140 mg/dL [3]. Ask a clinician about readings that worry you; FDA says not to act on OTC CGM readings without one [1].

Can I compare my CGM average to my A1C?

Not directly. In people without diabetes, the CGM-based estimate averaged 0.59 points above lab HbA1c [7].

Do Stelo or Lingo warn about low blood sugar?

No. Stelo is not designed to alert users to hypoglycemia, and Lingo has no glucose alarms [1][2].

More in Metabolic Health & Blood Sugar

References

  1. [1]FDA Clears First Over-the-Counter Continuous Glucose Monitor (March 5, 2024). U.S. Food and Drug Administration, 2024.
  2. [2]Lingo Glucose System 510(k) summary, K233655 (decision May 29, 2024). U.S. Food and Drug Administration, 2024.
  3. [3]Continuous Glucose Monitoring Profiles in Healthy Nondiabetic Participants: A Multicenter Prospective Study. J Clin Endocrinol Metab, 2019. PMID 31127824
  4. [4]Glucotypes reveal new patterns of glucose dysregulation. PLoS Biol, 2018. PMID 30040822
  5. [5]Personalized Nutrition by Prediction of Glycemic Responses. Cell, 2015. PMID 26590418
  6. [6]Imprecision nutrition? Different simultaneous continuous glucose monitors provide discordant meal rankings for incremental postprandial glucose in subjects without diabetes. Am J Clin Nutr, 2020. PMID 32766882
  7. [7]Discordance Between Glucose Management Indicator and Glycated Hemoglobin in People Without Diabetes. Diabetes Technol Ther, 2023. PMID 36790875

Dietary supplements are not intended to diagnose, treat, cure or prevent any disease, and these statements have not been evaluated by the FDA. Prescription options need a licensed clinician. Talk to your clinician or pharmacist before starting anything new, especially if you take prescription medicines, are pregnant or breastfeeding.

Keep reading: Supplements and vitamins

Supplements and vitamins: every page →Supplement & Nutrient Encyclopedia →Browse all topics →

Previous in this topicSoluble Fiber for Blood Sugar and LDL: Psyllium, Oats and Barley vs the FDA Health ClaimFDA lets qualifying foods link soluble fiber to lower heart-disease risk at 7 g a day from psyllium or 3 g of beta-glucan from oats or barley.Next in this topicMetabolic Health and Blood Sugar: Prediabetes, Glucose Monitors and Supplements, by the EvidenceLifestyle change cut new diabetes by 58% in the landmark prevention trial, more than metformin.Apple Cider VinegarApple cider vinegar is vinegar made by fermenting apple juice twice; its main active compound is acetic acid.GLP-1s for Women: What the Trials Show, What Compounded Really Means, and the Birth-Control CatchSemaglutide and tirzepatide produced 15% to 21% average weight loss in their main trials, and stopping led to regain.Psyllium Husk for Cholesterol: About 13 mg/dL Off LDL Across 28 TrialsPsyllium is one of the few supplements with both consistent trial data on LDL cholesterol and an FDA-authorized food-label health claim.

Evidence-graded supplement stacks →