Continuous Glucose Monitoring Without Diabetes: Signal or Noise?
Dr. RP, MD — Board-Certified, Emergency Medicine & Critical Care Medicine — Founder, Analog Precision Medicine
Three years into my physiology PhD at Queen's — before I left for medical school in Dublin — I spent a lot of time thinking about glucose kinetics in isolated tissue preparations. I understood glucose metabolism as a research problem before I ever saw it as a clinical one. Fast forward twenty years: I'm a runner wearing a CGM on my arm, not because I'm diabetic but because I wanted to see what my glucose was doing during runs, after meals, and during 3 AM granola bars in the ER.
What I found taught me something important about the difference between interesting data and clinically actionable data — a distinction that matters when a $100/month sensor is being marketed to healthy people.
What You'll See
Metabolically healthy people on CGM typically see fasting glucose of 70–100 mg/dL, postprandial spikes that rarely exceed 140 (usually under 120), and rapid return to baseline within 1–2 hours. There will be variability — that's normal physiology, not pathology.[1] The problem is that wellness marketing conflates normal postprandial excursions with metabolic disease. A glucose of 145 thirty minutes after pasta is not the same as a fasting glucose of 145. The first is digestion. The second is diabetes.
Where It Adds Value
Identifying occult insulin resistance. Prolonged postprandial elevations in patients with normal fasting glucose but elevated fasting insulin are exactly the pattern a CGM can reveal — confirming what the HOMA-IR already suggested.
Individual food responses. Two people eating identical meals can have dramatically different glucose patterns. A short CGM trial with a food diary generates actionable, personalized data.
Exercise optimization. Wearing a CGM during Zone 2 runs revealed how much glucose dropped during longer efforts, which changed fueling strategy in a way that quarterly A1c results never would.
Behavioral accountability. Immediate feedback from a CGM is more motivating than quarterly A1c results for many patients — the real-time signal changes behavior in a way lagged metrics don't.
Where It Creates Noise
Glucose anxiety. Some patients become hypervigilant, developing orthorexic-style food restriction over normal 130 mg/dL postprandial readings — a physiological response being treated as pathology.
Sensor inaccuracy. MARD of 8–10% means a true glucose of 95 might read 85–105, putting fine-grained meal comparisons within the noise floor.[2] The precision implied by continuous data isn't always real.
Overtreating normal physiology. Eliminating fruit because a CGM showed 125 after a banana is not metabolic optimization. That's what bananas do. The response is disproportionate to the signal.
The Clinical Framework
CGM is used selectively. For patients with suspected insulin resistance (normal fasting glucose but elevated insulin/HOMA-IR), a 2-week trial adds meaningful confirmatory data. For athletes and executives interested in nutrition optimization, a short trial with a food diary generates actionable insights. For established prediabetes, CGM adds value as part of a comprehensive strategy.
“The question isn't whether CGM data is interesting — it almost always is. The question is whether it's actionable in a way that improves outcomes.”
For metabolically healthy patients with normal insulin levels and no risk factors, it's generally not recommended. A well-interpreted fasting insulin and HOMA-IR provides more clinically relevant information at a fraction of the cost and cognitive burden. The question isn't whether CGM data is interesting — it almost always is. The question is whether it's actionable in a way that improves outcomes.
References
- 1.Shah VN, et al. CGM profiles in healthy nondiabetic participants. J Clin Endocrinol Metab. 2019;104(10):4356–4364.
- 2.Dexcom/Abbott CGM technical specifications: MARD and interstitial fluid glucose lag time.
Dr. RP, MD is dual board-certified in Emergency Medicine and Critical Care Medicine and is the founder of Analog Precision Medicine, a precision medicine practice in Southern California. This article is for educational purposes only and does not constitute medical advice or establish a physician-patient relationship.
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