The TL;DR
A Continuous Glucose Monitor (CGM) is a small sensor worn on the arm that measures interstitial fluid glucose 24/7. Originally for diabetics, it is now the premier tool for longevity optimization. It reveals exactly how your body responds to specific foods, sleep, stress, and exercise, moving nutrition from “general guessing” to “personalized engineering.”
Accessibility Level
Level 2 (Optimization): Requires a prescription in the US (though easy to get via services like Levels, Nutrisense, or Signos). Cost is ~300/month out of pocket. Not essential for everyone, but transformative for a 1-month experiment.
Why Wear a CGM if You Aren’t Diabetic?
The “Normal” Myth
Standard fasting glucose tests miss the movie. You can have a perfect fasting glucose of 85 mg/dL but spike to 180 mg/dL after lunch every day. These “silent spikes” drive insulin resistance and endothelial damage years before HbA1c rises.
Personalized Nutrition
There is no universal “low glycemic” diet.
- Person A eats a banana: Glucose stays flat.
- Person B eats a banana: Glucose spikes to 160.
- Person C eats a cookie: Glucose spikes, but a 10-minute walk flattens it.
A CGM tells you your “Glucotype.”
Behavioral Feedback
The “Hawthorne Effect” is powerful. When you see the spike caused by a soda, you are less likely to drink it again. It gamifies metabolic health.
What to Look For
The Metrics
- Time in Range (70-120 mg/dL): Aim for >95% of the day in this tight window.
- Peak Glucose: Aim to stay under 140 mg/dL (ideally 120 mg/dL) after meals.
- Variability (CV): A low standard deviation means stable energy and low oxidative stress.
- Recovery: How fast do you return to baseline? (Should be < 2 hours).
Common Insights
- Sleep Spikes: High carb dinners or alcohol often cause elevated glucose all night, destroying sleep quality.
- Stress Spikes: A stressful meeting can raise glucose as much as a candy bar (cortisol effect).
- Exercise Dips: A post-meal walk is the most effective drug-free way to blunt a spike.
Protocol: The 1-Month Experiment
You don’t need to wear one forever. Use it for 4 weeks to “map” your metabolism.
- Week 1 (Baseline): Eat normally. Don’t change anything. Observe the carnage.
- Week 2 (Elimination): Remove the obvious offenders (sugar, white flour). Watch the baseline drop.
- Week 3 (Experiments): Test specific foods. Rice vs. Potatoes. Fruit alone vs. Fruit with Greek Yogurt.
- Week 4 (Lifestyle): Test interventions. Walk after dinner. Cold plunge. Sauna. See what stabilizes you.
Evidence Matrix
| Source | Verdict | Notes |
|---|---|---|
| Peter Attia | Strongly Recommends | Considers it superior to HbA1c for understanding metabolic flux. |
| David Sinclair | User | Uses it to maintain steady levels, arguing spikes accelerate aging. |
| Weizmann Institute | Landmark Study | 2015 study showed massive individual variability in glucose response to identical foods. |
References
Zeevi, D., et al. (2015). Personalized nutrition by prediction of glycemic responses. Cell, 163(5), 1079-1094.
Hall, H., et al. (2018). Glucotypes reveal new patterns of glucose dysregulation. PLOS Biology, 16(7), e2005143.
Liao, Y., et al. (2020). Efficacy of continuous glucose monitoring in non-insulin-treated type 2 diabetes: A meta-analysis. Journal of Diabetes Investigation.