Who should not bother with a CGM, and what to do instead
Mis à jour 2026-08-07
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Réponse courte
Who should not buy a CGM?
If you are metabolically healthy with a normal HbA1c and no risk factors, a sensor is unlikely to tell you anything actionable, and a blood test costs a fraction of one. If you take insulin or a sulfonylurea, a consumer wellness sensor without alarms is the wrong device — you need one that can wake you.
Comment lire les étiquettes de preuve
Chaque affirmation de cette page porte une étiquette indiquant le poids qu’elle peut supporter. Elle décrit la solidité du résultat, non le prestige de la revue.
- Preuves solidesUn grand essai randomisé, une cohorte suivie longtemps, ou la concordance de plusieurs d’entre eux.
- Preuves émergentesRéel, mais mince — petit, court, observationnel ou non encore répliqué.
- ContestéDes chercheurs compétents sont en désaccord. Nous ne tranchons pas à votre place.
If you are already metabolically healthy
No trial has shown that wearing a sensor improves any health outcome in people whose glucose is normal and who have no risk factors. What you will get is a fortnight of data showing that you spike after meals, which is what a working metabolism does.
Monitoring studies make this concrete: people classed as normoglycaemic by standard tests still spend a meaningful share of their time in ranges labelled prediabetic. Buying a sensor to reassure yourself is likely to do the opposite, for reasons that have nothing to do with your health.
Ce que disent les preuves
Normoglycaemic people regularly register readings in the prediabetic range during continuous monitoring, so unremarkable physiology can read as alarming.1
Preuves émergentes
Popular sources attribute effects to glucose spikes — including on cancer risk, mood and sleep — that the peer-reviewed literature does not support.2
Preuves émergentes
If you take insulin or a sulfonylurea, buy carefully
This is a safety point, not a value-for-money one. Several of the cheapest sensors on this site are sold as wellness products and have no high or low alarms. If a drug you take can drive your glucose down while you sleep, a device that records the event for you to read about in the morning is not the right device.
Our recommendation quiz treats this as a hard filter rather than a preference: answer that you take insulin and every alarm-less device disappears from the results, even if it would otherwise rank first on price.
Ce que disent les preuves
Time below range is a distinct clinical concern with its own consensus target, separate from average glucose or time in range.3
Preuves solides
The cheaper tests that answer the same question
If your question is "am I heading towards diabetes", the instruments designed for that question cost far less than a sensor. An HbA1c gives you your average over two to three months in a single blood draw. A fasting glucose and fasting insulin taken together give an index of insulin resistance, which a CGM cannot produce at all. An oral glucose tolerance test is the most informative of the three.
A year of continuous sensor wear costs several hundred pounds or dollars in most of our markets. The blood tests above cost a fraction of that, and — unlike the sensor — the evidence base for acting on them is decades deep.
Ce que disent les preuves
If you are hoping it will tell you which diet suits you
This is the most common reason people buy a sensor and the one with the least support. A randomised trial of 609 adults tested precisely this idea — that a marker of insulin-glucose physiology would identify who should eat low-fat and who should eat low-carbohydrate — and found it did not.
The related theory that carbohydrate drives fat storage through insulin, and that this is why some diets work better, has had several of its key predictions tested in controlled feeding studies and not upheld. Competent researchers still disagree about parts of this, which is why we tier it as contested rather than settled — but a sensor is not going to resolve it for you personally.
Ce que disent les preuves
Baseline insulin secretion did not predict whether a person lost more weight on a low-fat or a low-carbohydrate diet in a 12-month randomised trial.6
Preuves solides
Several key predictions of the carbohydrate-insulin model of obesity were not upheld in controlled inpatient feeding studies, and the model remains disputed.7
Contesté
Questions fréquentes
- Is a CGM worth it for a healthy person?
- For curiosity, possibly — it is genuinely interesting to see your own responses. For health, there is no trial evidence of benefit in people who are already metabolically healthy, and a blood test answers the underlying question for much less.
- What is the cheapest way to check for insulin resistance?
- Fasting glucose and fasting insulin measured together, which a clinician can order and which a CGM cannot substitute for. An HbA1c tells you about the later stage, once glucose has started to rise.
- Can I use a wellness CGM if I take insulin?
- Devices sold as wellness products often lack high and low alarms and are not cleared for treatment decisions. If a medication you take can cause hypoglycaemia, that is the feature you cannot do without — talk to your prescriber before relying on any sensor.
Références
- 1.Hall H, Perelman D, Breschi A, Limcaoco P, Kellogg R, McLaughlin T, Snyder M (2018). Glucotypes reveal new patterns of glucose dysregulation. PLoS Biology. 10.1371/journal.pbio.2005143
- 2.Avner S, Robbins T (2025). A Scoping Review of Glucose Spikes in People Without Diabetes: Comparing Insights from Grey Literature and Medical Research. Clinical Medicine Insights: Endocrinology and Diabetes. 10.1177/11795514251381409
- 3.Battelino T, Danne T, Bergenstal RM, Amiel SA, Beck R, Biester T, et al. (2019). Clinical Targets for Continuous Glucose Monitoring Data Interpretation: Recommendations From the International Consensus on Time in Range. Diabetes Care. 10.2337/dci19-0028
- 4.Tabák AG, Herder C, Rathmann W, Brunner EJ, Kivimäki M (2012). Prediabetes: a high-risk state for diabetes development. The Lancet. 10.1016/S0140-6736(12)60283-9
- 5.Tabák AG, Jokela M, Akbaraly TN, Brunner EJ, Kivimäki M, Witte DR (2009). Trajectories of glycaemia, insulin sensitivity, and insulin secretion before diagnosis of type 2 diabetes: an analysis from the Whitehall II study. The Lancet. 10.1016/S0140-6736(09)60619-X
- 6.Gardner CD, Trepanowski JF, Del Gobbo LC, Hauser ME, Rigdon J, Ioannidis JPA, Desai M, King AC (2018). Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion: The DIETFITS Randomized Clinical Trial. JAMA. 10.1001/jama.2018.0245
- 7.Hall KD (2017). A review of the carbohydrate-insulin model of obesity. European Journal of Clinical Nutrition. 10.1038/ejcn.2016.260