Intro to continuous glucose monitoring (CGMs)

Continuous glucose monitors (CGMs) and biosensors help you see how your body responds to food, stress, and activity in near real time. If you are new to glucose data, the numbers and spikes can feel confusing at first. This guide explains what to look for and how to use your data to learn, not to judge.

Glucose monitoring 101

Rises in glucose are normal. Glucose typically rises and falls in response to eating, moving, and sleeping.
Variation is expected. The same meal can look different on different days depending on sleep, stress, or activity.
Biosensors are “accurate enough” for trends. Readings can vary slightly between sensors, and compared to fingerstick blood glucose, because sensors measure interstitial fluid (the fluid between your cells). What matters most is the pattern.

The goal is not perfect flat lines. The goal is to learn your patterns and support long-term metabolic health.

What is a glucose spike?

There is no single scientific definition. In Levels, a “spike” is a 30 mg/dL (or greater) rise above your baseline glucose.

Example

Baseline: ~100 mg/dL
Post-meal peak: 130 mg/dL
Rise: 30 mg/dL → this counts as a spike

Anatomy of a spike (what to pay attention to)

A spike is more than the peak number. Think of it as a curve with a few key features:

Peak height (rise above baseline): How high did you go?
Slope (speed of rise): Did glucose shoot up quickly or rise gently?
Time elevated (area under the curve): How long did glucose stay above baseline?
Return to baseline: How quickly (and smoothly) did you come back down?
- A common benchmark is returning to baseline within ~90 minutes.

Why this matters

Two spikes with the same peak height can mean very different things if one rises quickly, stays high for longer, or returns to baseline slowly.

Why the return to baseline matters

The rise tells you what happened after a meal. The return to baseline tells you how your body handled it.

Common patterns:

Quick, clean return: Often reflects an efficient metabolic response.
Slow return: Glucose stays elevated longer, which can signal reduced glucose clearance.
Drops below baseline (“rebound low”): A larger insulin response can push glucose lower than baseline, sometimes followed by cravings, shakiness, or fatigue.
Partial return: Glucose comes down, but not all the way back to baseline. This can happen when your system is under stress.

Key takeaway: The curve shape and recovery can be more informative than peak height alone.

Why numbers vary (and why it is normal)

Variation can come from both the device and your day-to-day biology.

Sensor-to-sensor variation

Different sensors can show slightly different absolute numbers.
Sensors measure glucose in interstitial fluid (not directly in blood), so there is a natural lag and calibration differences.

Day-to-day variation in your body

Even with the same meal, glucose can change based on:

Sleep quality
Stress
Exercise
Time of day
Menstrual cycle
What you ate in your previous meal

Bottom line: Do not get stuck on one-off numbers. Look for patterns over time.

How to respond to spikes

You do not necessarily need to eliminate spikes. The goal is to shape them in healthier ways.

Try these options:

Match carbs to your activity. Higher-carb meals often land better on days you move more.
Balance your plate. Add fiber, protein, and fat to slow glucose absorption.
Take a short walk after eating. A 10–15 minute walk can help muscles use glucose.
Experiment with meal order. Some people see flatter curves when they eat carbs last.
Watch portion sizes. Larger carb loads often create higher and longer spikes.

A helpful mindset: curiosity, not judgment

Your biosensor is not a grading system. It is a feedback tool.

Instead of “Was this good or bad?”, try:

“What context might have shaped this response?”
“What happens if I change one variable next time (timing, walking, portion, or meal composition)?”

Over time, many people see smaller areas under the curve and faster returns to baseline, which can reflect improving metabolic resilience.

Quick recap

Glucose fluctuations are normal.
Look at the shape of the curve and the return to baseline, not just the peak.
Variation across sensors and days is expected.
Use your data to learn and run small experiments.

Next step: Pick one meal this week to run a simple experiment (for example, add a 10-minute post-meal walk) and compare the curve shape to a similar meal without the walk.