Two November studies try to define a normal glucose curve in healthy people

Continuous glucose monitors are now sold to people without diabetes as a general metabolic feedback device, which creates an interpretive problem the technology was never built for. A monitor designed to flag hypoglycaemia and hyperglycaemia in a person with diabetes produces, in someone without it, a continuously wiggling line with no established definition of normal. Two studies published in November attempt to supply one, from opposite directions [s1][s2].

The benchmark attempt

The first, in Diabetes Technology & Therapeutics, targets a specific gap: reference ranges for glucose levels are well established, but no physiological benchmark exists for glucose rates of change, despite an association between rapid glycaemic fluctuation and adverse outcomes [s1].

The researchers analysed CGM data from 153 healthy, non-diabetic individuals wearing a Dexcom G6 for up to ten days [s1]. They calculated the percentage of time spent above various rate-of-change thresholds over 5-, 15-, 30- and 60-minute intervals, stratified by age and time of day [s1].

Measured over 15 minutes, the median time with a rate of change exceeding ±2 mg/dL per minute was small: 1.4% of time rising and 1.0% falling [s1]. Rates of change were slower when measured over longer intervals, faster when rising than when falling, faster during daytime hours, and showed modest differences across age groups [s1].

On that basis the authors propose ±2 mg/dL/min over 15 minutes as a normative reference, offered as analogous to the familiar 70–140 mg/dL glucose range [s1].

The proposal has an obvious dependency: it is derived from 153 people wearing one manufacturer's sensor for up to ten days [s1]. Rate-of-change estimates are sensitive to a sensor's smoothing algorithm, so the threshold is not automatically transferable to a different device.

The controlled-challenge attempt

The second study, published in PLOS Digital Health, comes at the same problem experimentally rather than observationally. The CGM-HYPE trial had ten participants wear a FreeStyle Libre 3 for fourteen consecutive days while completing nine standardised challenges: food, anaerobic and aerobic exercise, and the Trier Social Stress Test, a laboratory protocol for inducing acute psychosocial stress [s2]. It is registered in the German clinical trial registry [s2].

Individual glucose responses were assessed over four hours after each challenge using several metrics, including area under the curve, maximum glucose, time to maximum, glucose excursion, and a measure the authors call glucose recovery time to baseline [s2].

Three results stand out. Anaerobic exercise produced a significantly larger glucose excursion than aerobic exercise (28.7 ± 21.46 mg/dL versus 8.8 ± 4.91 mg/dL, p = 0.0228) [s2]. Carbohydrate-rich food produced the largest increase, at 161.4 ± 15.59 mg/dL [s2]. And the social stress test produced a significant change in baseline-corrected glucose over time (p = 0.0113) [s2].

What that last one implies for a consumer

The stress finding is the most directly relevant to how these devices are actually used. A person tracking their own glucose curve is generally told to attribute excursions to what they ate. The CGM-HYPE result indicates that a standardised psychosocial stressor — no food involved — produces a substantial glucose response in healthy young adults [s2].

That does not mean a spike after lunch was really about a meeting. It means the attribution is not straightforward, and that a device presented as measuring dietary response is measuring something with at least one other large input.

The exercise result cuts the same way. Anaerobic effort raised glucose more than three times as much as aerobic effort in this sample [s2]. A rise after a hard interval session is a normal physiological response, not a sign of dysregulation.

What neither study establishes

Neither is a study of whether wearing a CGM improves anything. Both describe what the signal looks like in people without diabetes; neither examines whether seeing that signal changes behaviour, weight, glycaemia or any clinical outcome.

Ten participants is very small, and the CGM-HYPE authors describe their trial as exploratory [s2]. The reference-range study is larger at 153 people but observational, with no clinical outcomes attached to the proposed threshold — the association between rapid fluctuation and adverse outcomes is cited as the motivation, not demonstrated here [s1].

There is also no evidence in either paper that a healthy person exceeding the proposed rate-of-change threshold should do anything about it. A reference range describes a distribution; it does not by itself define a problem.

What to watch

The useful next step from the reference-range paper would be validation across sensors and a larger, more diverse sample [s1]. From CGM-HYPE, replication of the stress finding at scale [s2]. And underneath both, the question the consumer market has largely skipped: whether any of these metrics, once defined, predict anything about a healthy person's future health.

Sources

• Normal Reference Range for Glucose Rates of Change in Nondiabetic Individuals Using Continuous Glucose Monitoring — Diabetes Technology & Therapeutics, 2025-11-20
• Continuous Glucose Monitoring under standardised conditions regarding diet, exercise and stress in Healthy Young People (CGM-HYPE study): An exploratory clinical trial — PLOS Digital Health, 2025-11-14