Different Brands of Continuous Glucose Monitors Yield Similar Measurements in Healthy Individuals

Continuous glucose monitors (CGMs) have become popular with non-diabetic people who want to track their glycemic responses to meals and adjust their diets accordingly. However, a study published in The American Journal of Clinical Nutrition in 2020 showed that when 16 healthy adults simultaneously wore two CGMs of different brands, meal rankings were about 50% discordant between brands.

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In a larger and more comprehensive study, Jordi Merino, PhD, a research associate in the Diabetes Unit of the Endocrine Division at Massachusetts General Hospital and Instructor in Medicine at Harvard Medical School, Andrew T. Chan, MD, MPH, director of cancer epidemiology in the Mass General Cancer Center, chief of the Clinical and Translational Epidemiology Unit and vice chair for clinical research in the Division of Gastroenterology, and professor of Medicine at Harvard Medical School, and colleagues came up with a different conclusion. Their findings, also published in The American Journal of Clinical Nutrition, suggest strong concordance in glycemic measures by different CGMs brands, which could support precision nutrition advice in healthy populations.

Methods

The researchers conducted a secondary analysis of ZOE PREDICT 1, a multicenter trial that investigated variations in postprandial responses to standardized and freely selected meals and foods in adults 18 to 65 years old. As reported in Nature Medicine, participants wore digital devices, including CGMs, and painstakingly recorded all food and drinks consumed using a smartphone app.

The 394 ZOE PREDICT participants included in this secondary analysis were monitored with two simultaneously worn CGMs between October 2019 and April 2021. Over a 14-day study period, they consumed 4,457 standardized meals and 5,738 freely selected meals.

360 of these individuals wore two Abbott Freestyle Libre Pro CGM (FSL) throughout the study period, and 34 wore both the FSL and the Dexcom G6 CGM (DEX).

Glycemic Responses

The primary outcome was the repeatability of CGM measures for the incremental area under the glucose curve at 2 hours (a parameter to quantify glycemic excursions after glucose loading) :

• Standardized meals—The coefficient of variation (CV: a measure of the dispersion of the data; if it is high, it means there is disagreement between measurements) was 3.7% for intrabrand comparisons and 12.5% for interbrand comparisons
• Freely selected meals—CVs were 4.1% and 16.6%
• Freely selected meals containing >25 g carbohydrate—CVs were 4.4% and 15.2%

Other Key Findings

• Meal rankings for the incremental area under the glucose curve at 2 hours—Correlation coefficients were 0.87 and 0.68
• Time in which glycemia is between 70 and 180 mg/dl—CVs were 4.8% and 3.2%
• Glucose CV—19.4% in participants wearing FSL only and 18.2% in those wearing FSL + DEX

The Promise of Precision Nutrition

All glycemic metrics studied were concordant between devices of the same brand. This demonstrates the efficacy of CGMs in capturing different features of a healthy individual's glycemic response to consumed study meals and freely elected foods.

The agreement between devices of different brands was slightly lower but still considerable, suggesting meal categorization is not only device-independent but also unbiased by brand.

These encouraging findings imply that CGM measurements can someday be used for precision nutrition advice for healthy individuals.

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