CGM automatically records interstitial fluid glucose concentration every 5-15 minutes via subcutaneously implanted microsensors, reflecting glucose dynamics in real time. Abbott FreeStyle Libre, domestic Chinese brands (Sibionics), and Dexterity G6/G7 are major products. Non-diabetic motivations for CGM use: understanding food’s glycemic impact, optimizing exercise timing, and identifying metabolic risk factors.
## Key Glucose Metric Interpretation
**Fasting blood glucose**: normal range 3.9-6.1 mmol/L (70-110 mg/dL); ≥6.1-7.0 mmol/L = impaired fasting glucose (pre-diabetes warning); ≥7.0 mmol/L = diagnostic criterion for diabetes (requires two confirmations).
**Postprandial glucose peak (PPBS)**: normal individuals peak 30-60 minutes post-meal, typically not exceeding 7.8 mmol/L (140 mg/dL), returning to baseline within 2 hours. Postprandial glucose chronically exceeding 7.8 mmol/L indicates postprandial hyperglycemia — an early metabolic abnormality signal even with normal fasting glucose.
**Glycemic Variability (GV)**: the amplitude of all-day glucose fluctuations, measured by standard deviation (SD) or coefficient of variation (CV). High GV (large glucose swings) causes more vascular and cognitive damage than sustained hyperglycemia. Target: intra-day glucose fluctuation amplitude <3 mmol/L. ## Weizmann Research: Evidence for Personalized Nutrition Eran Segal and Eran Elinav's team (Weizmann Institute of Science, Israel; 2015 Cell) had 800 subjects wear CGMs continuously for 7 days while recording detailed diet, lifestyle, and fecal microbiome. The results shocked the nutrition field: **postprandial glucose responses to the same food varied enormously between individuals** — one person's blood glucose spiked with white rice while another's barely changed with the same amount. The most important predictor of this variation was **gut microbiome composition** (rather than a food's GI value). Personalized dietary recommendations (based on each individual's CGM data and microbiome) significantly outperformed standard low-GI diet advice for blood glucose control. See [Digital Health Overview](https://sunqi.org/digital-health-overview-en/) and [Levels Health CGM App](https://www.levelshealth.com/).
