- Continuous glucose monitors overestimated blood sugar levels in non-diabetic people in a small study.
- More health-conscious people are wearing the devices that were FDA-approved for over-the-counter sale last year.
- While useful for diabetics, most people who can regulate their blood sugar don’t need CGMs, experts said.
Continuous glucose monitors overestimated the blood sugar levels of non-diabetic people in a small study, calling into question how useful the buzzy devices are for the average person.
Researchers from the University of Bath, UK, compared the results of one brand of CGM with the gold-standard finger prick test when measuring the blood glucose levels of 15 non-diabetic people.
CGM patches provide data on blood sugar with a delay of up to 20 minutes using a sensor placed under the skin with a small needle. Because of the way they collect blood from users, the researchers hypothesized that they may give different results to finger-prick tests.
They found that the CGMs consistently overestimated blood sugar levels by 30% after the participants consumed fruits in various forms: including whole, blended, and smoothies by a brand available in UK grocery stores. The results were published in The American Journal of Clinical Nutrition on Wednesday.
The authors said the smoothie company Innocent Drinks funded the study but had no other involvement.
CGMs were designed for diabetics. But in recent years they have grown in popularity among health-conscious people interested in how different foods affect their blood sugar levels, in the hope of preventing chronic diseases and maintaining a healthy weight.
Last March, the US Food and Drug Administration changed their approval of CGMs from prescription-only to over-the-counter, meaning anyone could buy one.
Javier Gonzalez, a professor of nutrition and metabolism at the University of Bath and the study’s lead researcher, said that CGMs are “fantastic tools” for people with diabetes.
“However, for someone with good glucose control, they can be misleading based on their current performance,” Gonzalez said. “For healthy individuals, relying on CGMs could lead to unnecessary food restrictions or poor dietary choices.”
The authors acknowledged that the study was limited because they tested one brand of CGM, and the relatively small number of participants meant the results might not be relevant to the wider population.
Tijana Simic
Non-diabetics should take blood sugar readings with a pinch of salt
Experts not involved in the study agreed that CGMs may be causing unnecessary worry in non-diabetics.
Nicola Guess, an academic dietitian and researcher at the University of Oxford who specializes in the dietary prevention and management of type 2 diabetes, said the study suggests that CGMs may wrongly lead non-diabetic people to believe they have pre-diabetes.
This is not the first study to flag inaccuracies with CGMs, so non-diabetic people should take the data they provide with a pinch of salt — or not use them at all, Guess said.
Responding to the study, Adam Collins, an associate professor of nutrition at the University of Surrey, UK, referenced his own ongoing research, which found that two CGMs worn on different arms of the same person logged different data.
Guess previously explained to BI why, if you don’t have diabetes or pre-diabetes, blood sugar fluctuations are nothing to worry about.
“When we’re considering CGMs in healthy people, it is perfectly normal for your blood glucose to go up and down. It shouldn’t be flat, so don’t aim for flat. And I think that will help a lot of people relax,” Guess said.
There’s no evidence to suggest that a blood sugar rise is always followed by a stark drop or causes hunger either, she said.
Charles Brenner, a biochemist who chairs the Department of Diabetes and Cancer Metabolism at City of Hope in Los Angeles, told BI that data from CGMs can cause people to be more alarmed than they need to be.
However, CGMs may have some uses for non-diabetics. BI’s Gabby Landsverk previously spoke to an endurance athlete who used one, with the help of a sports dietitian, to learn that she had more energy if she ate more food, including complex carbs, and ate earlier in the day.
And a woman who was pre-diabetic told Landsverk tracking blood sugar levels helped her understand the foods that best suited her lifestyle, helping her to lose weight.
