Glucose Is Insulin's Shadow: What Consumer Glucose Sensors Can (and Can't) Tell You Without Diabetes

Glucose Is Insulin's Shadow: What Consumer Glucose Sensors Can (and Can't) Tell You Without Diabetes

Educational content, not medical advice. Talk with your physician before changing your diet, medication or testing routine.

Key takeaways

  • Small, short-term benefit. A January 2026 meta-analysis of 23 studies (1,074 adults without diabetes) found that wearing a continuous glucose monitor (CGM) modestly lowered average glucose, mainly in people with prediabetes, not in people with normal glucose. It did not change BMI significantly.
  • Glucose may hint at insulin. A preprint posted 4 November 2026 (not peer reviewed) reports that in adults without diabetes, average CGM glucose tracked insulin resistance markers better than HbA1c did. It is cross-sectional and company-linked, so treat it as a hypothesis.
  • A sensor is a biofeedback tool, not a test. In the US, over-the-counter CGMs are cleared for wellness use in adults not on insulin. They are not meant to diagnose diabetes or prediabetes.

01 / Why glucose is only half the story

Insulin is a hormone made by the pancreas. After a meal, it moves glucose out of the blood and into tissues. When tissues respond poorly (insulin resistance), the pancreas can compensate by making more insulin. Glucose can then stay normal for years while insulin is already high. Standard screening looks at glucose (fasting glucose, HbA1c), so early insulin resistance can be missed. That is the appeal of looking at glucose in more detail, and the reason to be careful about what it can show.

02 / What the 2026 meta-analysis found

Liao and colleagues (European Journal of Medical Research, January 2026) searched four databases through December 2025 and included 23 studies: 7 randomized trials plus cohort, observational and cross-sectional designs, 1,074 non-diabetic participants in total. Mean blood glucose was lower with CGM than with controls (standardized mean difference -0.54, 95% CI -1.02 to -0.07). BMI did not change significantly. The glucose benefit appeared in people with prediabetes but not in people with normal glucose. CGM was linked to better adherence and some dietary changes. The authors suggest using CGM as biofeedback inside structured lifestyle programs, and say it is unlikely to reach weight goals on its own.

A broader 2024 meta-analysis of 25 randomized trials (2,996 people, mostly with type 2 diabetes) found CGM feedback lowered HbA1c by 0.28 percentage points (95% CI 0.15 to 0.42), with high heterogeneity (I² 88%). Eleven of the 25 trials reported conflicts of interest tied to CGM companies. Only a few trials measured diet or activity, so why it helps is still unclear.

03 / The new insulin signal (preprint)

On 4 November 2026, Ginart and Loesche posted a medRxiv preprint using data from the Levels platform: 62,122 free-living adults, of whom 7,930 without diabetes had lab data. Average glucose was the most stable week-to-week measure (intraclass correlation 0.747). Among people without diabetes, average glucose explained about three times more variance in fasting insulin than HbA1c did (R² 0.131 vs 0.048). Among people with a normal HbA1c, fasting insulin of 10 µIU/mL or more was about twice as common when average glucose was 110 mg/dL or higher (27.5% vs 12.6%).

Read this cautiously. It is a preprint. It is cross-sectional, so it cannot show who goes on to develop disease. App users are self-selected. Even the stronger R² of 0.131 means most of the variation in fasting insulin is not explained by CGM glucose. The authors consult for the company whose data they analyzed.

04 / What's new in regulation

United States. The FDA cleared the first over-the-counter CGM, Dexcom's Stelo, on 5 March 2024, for adults 18 and older who do not use insulin, including people without diabetes who want to understand how diet and exercise affect their glucose. The FDA noted that it is not for people with problematic hypoglycemia, and that users should not make medical decisions from the output without talking to a clinician. On 10 June 2024 Abbott announced clearance of two OTC systems: Lingo, for adults not on insulin who want to improve general wellness (not intended to diagnose disease, including diabetes), and Libre Rio, for adults with type 2 diabetes not on insulin. On 6 January 2026 the FDA also revised its General Wellness guidance for low-risk devices; as summarized by law firms (I did not read the FDA text), wellness products must avoid disease claims and diagnostic thresholds.

European Union. On 2 December 2025, IDF Europe asked the European Commission to strengthen CGM oversight under the MDR, stating that there is no EU-level device-specific guidance for evaluating CGM accuracy and that some CE-marked CGMs have been found not fit for purpose. This is an advocacy position, not a regulatory decision.

Key figures

For clinicians

  • Liao 2026 (Eur J Med Res): Systematic review with meta-analysis; PubMed, Cochrane, Web of Science, Embase to Dec 2025; 23 studies (7 RCTs, 1 cohort, 7 prospective observational, 4 cross-sectional, 4 clinical trials); n = 1,074 non-diabetic. Mean glucose SMD -0.54 (95% CI -1.02 to -0.07, P = 0.03); BMI SMD -0.25 (-0.63 to 0.12); accuracy MD -3.90 mg/dL (P = 0.40). Benefit in prediabetes, not normoglycemia.
  • Richardson 2024 (IJBNPA): 25 RCTs, n = 2,996; HbA1c -0.28% (0.15 to 0.42), time in range +7.4% (2.0 to 12.8); I² 88% and 80.5%; 68% of trials in type 2 diabetes; 44% reported CGM-industry conflicts.
  • Ginart & Loesche 2026 (medRxiv preprint): Cross-sectional, n = 62,122, lab subset n = 7,930; fasting insulin R² 0.131 (mean glucose) vs 0.048 (HbA1c); spike width, not height, related to insulin resistance markers at equal mean glucose.
  • Limitations: I only had access to the abstract of Liao 2026, so its risk-of-bias and certainty ratings are unknown. Mixed designs, small samples, short follow-up, heterogeneous controls. No outcome trials in normoglycemic adults. No validated "normal" CGM ranges for healthy people were established by these sources.
  • Practice point: Do not use CGM output to diagnose or exclude dysglycemia. Use standard testing (fasting glucose, HbA1c, OGTT) and consider CGM as a behavioral adjunct only when the patient wants it.

What this means for patients

If you do not have diabetes, a glucose sensor may help you notice how meals, sleep and activity affect your glucose. The best evidence is for people with prediabetes, and the effects are modest. It will not diagnose anything, and it cannot measure your insulin. If you have a history of disordered eating, diabetes, or take glucose-lowering drugs, talk with your clinician first. If your readings worry you, ask for standard lab tests rather than relying on an app.

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References

  1. Liao X, Li Y, Tang S, Xiao Y, Yu X, Huang R, Zhong T. Continuous glucose monitoring in non-diabetic populations: a systematic review of observational and interventional studies with meta-analysis. Eur J Med Res. 2026 (Jan). doi:10.1186/s40001-026-03920-0. PMID 41588451.
  2. Richardson KM, Jospe MR, Bohlen LC, Crawshaw J, Saleh AA, Schembre SM. The efficacy of using continuous glucose monitoring as a behaviour change tool in populations with and without diabetes: a systematic review and meta-analysis of randomised controlled trials. Int J Behav Nutr Phys Act. 2024;21:145. doi:10.1186/s12966-024-01692-6. PMID 39716288.
  3. Ginart P, Loesche MA. Consumer continuous glucose monitoring uncovers hidden metabolic risk in free-living adults without diabetes. medRxiv preprint, posted 4 Nov 2026 (not peer reviewed). doi:10.64898/2026.11.03.26367126.
  4. US FDA. FDA Clears First Over-the-Counter Continuous Glucose Monitor. News release, 5 Mar 2024. https://www.fda.gov/news-events/press-announcements/fda-clears-first-over-counter-continuous-glucose-monitor
  5. Abbott. Abbott Receives U.S. FDA Clearance for Two New Over-the-Counter Continuous Glucose Monitoring Systems. Press release, 10 Jun 2024. https://abbott.mediaroom.com/2024-06-10-Abbott-Receives-U-S-FDA-Clearance-for-Two-New-Over-the-Counter-Continuous-Glucose-Monitoring-Systems
  6. IDF Europe. IDF Europe calls for stronger EU standards for CGMs. 2 Dec 2025. https://idf.org/europe/news/idf-europe-calls-for-stronger-eu-standards-for-cgms/
  7. US FDA. General Wellness: Policy for Low Risk Devices (revised guidance), 6 Jan 2026. https://www.fda.gov/media/90652/download (date and content via law-firm summaries; FDA text not opened this run).