Continuous Glucose Monitoring Can Overestimate Your Blood Sugar Levels, Study Finds - Video

Continuous Glucose Monitors (CGMs) are growing in popularity but new peer-reviewed research, published in The American Journal of Clinical Nutrition, from the University of Bath, suggests they may not be as accurate as many believe. Originally designed to help people living with diabetes manage their blood sugar, these devices are now being used by the health-conscious to track how different foods affect their glucose levels.

The research measured blood sugar responses in healthy volunteers using two methods: a CGM and the gold standard finger-prick test.

The research aimed to assess the accuracy of CGMs in measuring responses to various fruit-based products, ranging from whole fruit to smoothies.

The results showed that when participants consumed a smoothie, the Abbott Freestyle Libre 2 CGM overestimated the GI by 30%, reporting a GI of 69 compared to the traditional test result of 53.

Whole fruit was misclassified as medium or high-GI foods by CGMs, while the finger-prick test showed they were low-GI. This could lead users to mistakenly believe that fruit could cause harmful spikes in blood sugar.

CGMs overestimated the time spent above the blood sugar level threshold by nearly 400%, potentially causing unnecessary worry for people whose blood sugar is actually well-controlled.

The research concludes that CGMs are unlikely to be a valid method to determine whether a food is high or low-GI.

Ref: Katie M. Hutchins, James A. Betts, Dylan Thompson, Aaron Hengist, Javier T. Gonzalez,

Continuous glucose monitor overestimates glycemia, with the magnitude of bias varying by postprandial test and individual – A randomized crossover trial.,

The American Journal of Clinical Nutrition, 2025, ISSN 0002-9165, https://doi.org/10.1016/j.ajcnut.2025.02.024.