MARY LOUISE KELLY, HOST:
It's a small device, but the hype around it is huge. The technology is called constant glucose monitoring, and companies that make it say it will transform the way you feel. But what do scientific studies say? Michaeleen Doucleff finds out.
MICHAELEEN DOUCLEFF, BYLINE: The monitor is about the size of a quarter, and it sticks to the back of your arm. Every few minutes or so, it sends a signal to your phone estimating the concentration of sugar in your blood. Elizabeth Selvin at Johns Hopkins University says this technology is super helpful for managing diabetes.
ELIZABETH SELVIN: For patients and the families of people with Type 1 diabetes, I mean, it's been, you know, truly revolutionary.
DOUCLEFF: Helping people avoid dangerously low blood sugar. But last year, the FDA approved the first over-the-counter versions of continuous glucose monitors for people without diabetes. The idea is that they may help people lose weight and improve their overall health. Sarah Berry is a nutritionist at King's College London and chief scientist at the company Zoe, which distributes the monitors. She says everyone has blood sugar spikes when they eat carbohydrates.
SARAH BERRY: Peaks and troughs in glucose is a normal physiological response to consuming carbohydrates.
DOUCLEFF: But problems can arise when these surges are too big for too long.
BERRY: Having really high levels over a long period of time can increase your risk of some chronic diseases.
DOUCLEFF: Like heart disease, obesity and Type 2 diabetes. So in theory, a continuous glucose monitor could help people lower their blood sugar levels and reduce their risk for these problems. Several studies have tested that theory. Collin Popp, a nutritionist at New York University, helped to lead one of them. That study found that, on average, the glucose monitors did not help people lower their blood sugar very much at all.
COLLIN POPP: We actually found no real effect. We didn't find any significant results.
DOUCLEFF: And the monitoring didn't help people lose weight any better than simply following a traditional low-fat diet. But Popp says those negative findings were the average outcome and not the full story.
POPP: Some people did really well. We had individuals coming back to us, being like, you changed my life. I lost 30 pounds. I feel great.
DOUCLEFF: While others in the study gained weight. So scientists are now trying to figure out who benefits from this technology. Karen Kennedy, a private nutritionist, says the devices help some people make a big discovery about themselves - they're extremely sensitive to carbohydrates, even the healthy ones.
KAREN KENNEDY: Brown rice, quinoa, beans, grains - every time they eat it, their blood sugar goes too high, and it's consistently that way.
DOUCLEFF: Then if they eat fewer carbohydrates...
KENNEDY: Their blood sugar comes down dramatically. They feel better. They lose visceral fat.
DOUCLEFF: And she says when you wear the glucose monitor, you log what you eat. This helps people be more aware of how different foods impact their blood sugar.
KENNEDY: They're like, oh, when I eat this, my blood sugar goes up, and if I don't, it doesn't. And as soon as they change it, they're like, oh, that's an improvement.
DOUCLEFF: And that improvement motivates some people to eat better. Each device lasts about two weeks and costs about $50. But if you're thinking of buying one, NYU's Collin Popp warns that the data can often be confusing for a lot of people.
POPP: If you give someone a bunch of data and they don't know what to do with it, what's the point?
DOUCLEFF: So he says there needs to be more guidance and education about this new technology.
For NPR News, I'm Michaeleen Doucleff. Transcript provided by NPR, Copyright NPR.
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