Continuous Glucose Monitors Without Diabetes:
Useful Insight or Unnecessary Worry?

Continuous glucose monitors (CGMs) are small sensors worn on the arm that measure glucose in the fluid under the skin every few minutes. They've transformed diabetes care, and they're now sold to people without diabetes as a way to "optimise" metabolic health. In 2024, the US Food and Drug Administration cleared the first CGM available without a prescription. But what's normal, and does wearing one improve health? In healthy adults without diabetes, glucose stays between 70 and 140 mg/dL (3.9-7.8 mmol/L) about 96% of the time, and short rises after meals are completely normal. Studies show that people respond very differently to the same foods, which is interesting and can motivate change. But there's no evidence yet that wearing a CGM improves long-term health in people without diabetes, the devices are less precise at normal glucose levels, and chasing a "flat line" can cause unnecessary worry. This article sets out what a CGM can and can't tell you.

Key numbers

How a CGM works

A CGM has a tiny filament inserted just under the skin, usually on the back of the upper arm, attached to a sensor that sends readings to a phone app. It measures glucose in the interstitial fluid around cells rather than in blood, so readings lag blood glucose by several minutes and can differ from a finger-prick test. Sensors typically last 10-15 days.

For people with type 1 diabetes, and type 2 diabetes treated with insulin, CGMs clearly improve glucose control and safety. The question here is whether they help people without diabetes.

Evidence strength

Strong: what normal glucose looks like. A multicentre study fitted 153 healthy people without diabetes, aged 7-80, with a CGM for up to 10 days. Average glucose was 98-99 mg/dL (about 5.5 mmol/L), rising to 104 mg/dL in people over 60. Glucose stayed between 70 and 140 mg/dL for a median of 96% of the time, was above 140 mg/dL for about 2.1% of the time (around 30 minutes a day) and below 70 mg/dL for about 1.1% (around 15 minutes a day). In other words, short rises after meals, and occasional low readings, are part of normal physiology.

Moderate: some people with "normal" tests have larger spikes. A 2018 study in 57 people found that even individuals classed as normal on standard tests showed considerable glucose variability on a CGM, with glucose in the prediabetes range 15% of the time and the diabetes range 2% of the time. The researchers grouped people into "glucotypes" by their pattern of responses and found the underlying physiology, insulin resistance or reduced insulin secretion, varied between people. Whether these patterns predict future diabetes or heart disease in people with normal standard tests isn't yet known.

Moderate: people respond differently to the same foods. In a 2015 study, 800 people wore CGMs for a week while their responses to 46,898 meals were recorded. Responses to identical meals varied widely between people, depending on factors such as the gut microbiome, body composition and activity. A small randomised trial within the study, in 26 people, found that diets personalised to each person's predicted responses lowered post-meal glucose. This supports the idea that there's no single "good" or "bad" food for everyone, and that a CGM can reveal your own patterns.

Limited: using a CGM to change behaviour. Seeing your glucose respond to a sugary drink, a large portion of white rice, a walk after dinner or a poor night's sleep can be motivating, and some people use this feedback to make lasting changes. But the evidence for health benefits in people without diabetes comes mainly from small, short studies.

Not established: CGMs improve long-term health in people without diabetes. There are no trials showing that wearing a CGM reduces diabetes, heart disease or death in people without diabetes. Reviews of CGM use in healthy adults conclude that the relevance of glucose patterns for health in this group is still largely unknown and that more research is needed.

Not supported: aiming for a "flat line". Rises after meals are normal. Avoiding all glucose spikes isn't an evidence-based goal, and restricting healthy carbohydrate foods such as fruit, pulses and whole grains to flatten the curve could make the overall diet worse.

Limitations and risks

• Less precise at normal levels: CGMs are designed and validated mainly for diabetes. At normal glucose levels, readings can differ meaningfully from blood tests, and night-time "lows" can be caused by lying on the sensor.
• Over-interpretation: a single spike tells you little on its own. The glucose response depends on meal size, what you ate with it, the time of day, sleep, stress and activity.
• Anxiety and food fear: constant monitoring can make some people anxious about eating. People with a history of disordered eating should be cautious.
• Cost: sensors need replacing every 1-2 weeks.
• Not a diagnostic test: a CGM doesn't diagnose diabetes or prediabetes. That still needs a fasting glucose, HbA1c or glucose tolerance test.

Recommendations by situation

If you have prediabetes or insulin resistance, see Insulin Resistance for the changes that make the biggest difference.

Practical notes

In people without diabetes, glucose stays in a narrow range most of the day, and short rises after meals are normal. A CGM can reveal how your body responds to different meals, sleep and exercise, and some people find this motivating, particularly if they have prediabetes or insulin resistance. But there's no evidence yet that wearing one improves long-term health in people without diabetes, the readings are less precise at normal levels, and chasing a flat line can backfire. The proven foundations of metabolic health, such as regular activity, a diet built around whole foods, good sleep and a healthy waist size, matter far more than any single glucose reading (see What Metabolic Health Really Means).