Continuous Data & Biometric Tracking

Continuous glucose monitors (CGMs) were designed for people with diabetes. In 2024, the FDA approved specific CGMs for use without a prescription — including for people without diabetes. This changed everything for the biohacking world.

What CGMs Actually Measure A CGM is a small sensor worn on the arm or abdomen that measures interstitial glucose (the glucose in fluid between your cells) every few minutes, 24 hours a day. This gives you a continuous graph of your blood sugar throughout the day instead of a single snapshot.

What Peer-Reviewed Research Shows A 2025 systematic review published in MDPI Sensors analyzed the evidence for CGM use in non-diabetic individuals for cardiovascular prevention. The review found that CGMs can detect abnormal blood glucose patterns in people without diabetes — patterns that standard fasting glucose tests completely miss. Non-diabetic individuals can exhibit glucose fluctuations that contribute to cardiovascular risk through increased inflammation, endothelial dysfunction, and oxidative stress.

A 2024 review in Diabetic Medicine (Wiley) noted that real-time glucose feedback can meaningfully change dietary and exercise behavior. Seeing exactly how a meal affects your blood sugar in real time creates immediate motivation to adjust. However, the same review found that more than 50% of positive research in this space is industry-sponsored, which warrants careful interpretation.

What CGMs Reveal About Gut Health Here is what consistently surprises first-time CGM users: foods that seem healthy often spike blood sugar significantly. White rice, oat milk, bananas, and even some protein bars can trigger glucose spikes above 140 mg/dL in some individuals — a level associated with increased oxidative stress and inflammation. Meanwhile, the same foods cause minimal response in others. This variability is largely driven by your gut microbiome. A landmark study from the Weizmann Institute in Israel found that personalized nutrition recommendations based on microbiome data produced better glucose outcomes than standard dietary guidelines.

What CGMs Cannot Tell You CGMs do not measure ketones, insulin levels, inflammation markers, or gut bacteria composition directly. They also cannot diagnose pre-diabetes or diabetes — that requires a blood test with a doctor. The FDA has warned consumers against using smartwatches or smart rings that claim to measure blood glucose without piercing the skin, as none are currently authorized for this purpose.

The Three Most Common CGMs in 2025 Dexcom Stelo: FDA-cleared for non-diabetics. $99 per month. 15-day wear. Abbott Lingo: FDA-cleared for non-diabetics. $49 for a 14-day sensor pack. Levels Health: Dexcom sensor plus software platform. $199 to $399 per month.

What We Recommend For gut health optimization specifically, a 30-day CGM trial is one of the most informative experiments you can run. You will likely discover 3 to 5 foods you thought were healthy that are spiking your glucose — and therefore driving inflammation that affects your gut lining and microbiome. After the trial, most people can maintain the habits without continued CGM use.

Three wearables dominate the biohacking market. Each measures different things, costs different amounts, and serves different types of users. Here is what each actually does well and where each falls short — based on published accuracy studies, not marketing.

Heart Rate Variability (HRV) — The Gut-Brain Connection Metric HRV is the variation in time between your heartbeats. A higher HRV generally indicates better vagal tone (a measure of how well your vagus nerve — the main gut-brain highway — is functioning) and better recovery. All three devices measure HRV, but at different times and with different methodologies.

Oura Ring: Measures HRV during sleep using a photoplethysmography (PPG) sensor on the finger. Published research shows finger-based PPG during sleep produces the most accurate HRV readings outside of a clinical ECG. Oura's sleep staging has been validated in multiple independent studies.

WHOOP: Measures HRV continuously and overnight. Uses a wrist-based sensor. Wrist-based HRV measurements are generally less accurate than finger-based during sleep but WHOOP's strain and recovery scores are well-regarded among athletes.

Apple Watch: Measures HRV during breathing exercises or sporadically during sleep (with watchOS 9 and later). Less focused on HRV as a daily metric. Strong for ECG spot-checks and fall detection. Excellent general fitness and activity tracking.

Sleep Tracking Accuracy A 2023 study published in NPJ Digital Medicine found that consumer wearables generally overestimate total sleep time and have varying accuracy for sleep staging. Oura Ring performed best among the three for sleep staging in independent validations. WHOOP performed well for strain and recovery metrics. Apple Watch improved significantly with newer models but still lags for detailed sleep staging.

What None of Them Can Do None of these devices can directly measure gut health, microbiome composition, cortisol levels, blood glucose (except Apple Watch Series 9 Ultra in limited testing), or inflammation markers. They are proxies — useful ones, but proxies. Do not make clinical health decisions based solely on wearable data.

Our Recommendation by User Type For gut health and stress monitoring: Oura Ring (best HRV and sleep data, most gut-brain relevant metrics) For athletes and recovery optimization: WHOOP (best strain and readiness scores) For general health and convenience: Apple Watch (best ecosystem, most features beyond health tracking)

2025 Pricing Oura Ring Gen 4: $299 hardware plus $5.99 per month subscription WHOOP 4.0: Free hardware with $30 per month subscription Apple Watch Series 10: $399 to $499, no subscription required