Continuous Glucose Monitoring: The Complete Guide

A continuous glucose monitor is a small sensor worn on your arm that measures glucose in interstitial fluid every 1–5 minutes, streaming data to your phone. Unlike finger-prick tests that give one snapshot, CGMs reveal the complete glucose curve after every meal, workout, and night of sleep.

Originally developed for diabetics, CGMs are now used by biohackers and health optimizers to understand metabolic health before disease develops. Levels, Nutrisense, and Signos wrap medical-grade sensors in apps that score meals and track trends.

Glucose spikes above 140 mg/dL trigger insulin release, inflammation, and oxidative stress, even in non-diabetics. Over years, repeated spikes drive insulin resistance, weight gain, brain fog, and increased disease risk.

The counterintuitive finding from CGM data: many 'healthy' foods spike glucose hard in specific individuals. Oatmeal, grapes, sushi rice, and green smoothies are common surprises. Meanwhile, some 'unhealthy' foods produce flat responses in certain people.

Stable glucose (rarely exceeding 110 mg/dL post-meal) correlates with stable energy, better focus, reduced cravings, and easier weight management, without calorie counting.

Your personal spike foods, the surprises are the value. Most users discover 3–5 'healthy' foods they should avoid and 3–5 foods they can eat freely.

Behavioral hacks that work: walking 10 min after meals (30–50% spike reduction), eating vegetables and protein before carbs (blunts spike), apple cider vinegar before meals (modest reduction), and avoiding naked carbs without fat/protein.

Sleep and stress impact: one bad night of sleep can increase next-day glucose spikes by 20–30%. Stress hormones directly raise blood sugar.

r/Levels and r/Biohackers consensus: CGM is the single most behavior-changing health tool. Users permanently alter diets after one 14-day sensor cycle.

Cost debate: Levels ($199/mo) vs Stelo ($99/mo OTC Abbott sensor) vs Dexcom. Stelo is the budget entry; Levels has the best app UX. Most recommend 1–3 months then intermittent check-ins.

Dave Asprey's advice: 'Everyone should wear a CGM for at least one month. You'll never look at food the same way.'