“Learn how the food you eat, the way you exercise, your sleep quality, and your stress patterns affect your blood sugar (glucose),” says Signos.com, one of a handful of companies that sell continuous glucose monitors (CGMs). “This is the Signos approach to healthy weight loss.”

Many people with type 1 diabetes—they produce no insulin—wear CGMs to let them know if their blood sugar is too high or low.

But it’s not clear if anyone else needs the devices, especially if weight loss—not controlling blood sugar—is the goal.

(The FDA has approved CGMs only for people with diabetes, but doctors can write an “off label” prescription for anyone. “Rest assured, an independent physician will handle the prescription for you,” says Signos, which charges $99 to $299 a month depending on how many months you sign up for.)

How accurate are CGMs?

Clearly, CGMs are accurate enough to detect dangerously high or low glucose levels.

But “companies are promising to unlock your unique solution for a healthy metabolism by measuring your glucose responses,” says Kevin Hall of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

How well can the devices measure glucose responses in people without diabetes? “We often found very different glucose responses to the same meals when people simultaneously wore two CGMs,” says Hall.

His study tested the Dexcom G4 Platinum and the Abbott Freestyle Libre Pro in 16 volunteers who lived at an NIDDK lab for four weeks.

Hall’s team also looked at one CGM’s results for the same meal eaten by the same person on two days roughly a week apart. The results were similar but far from identical.

“Are these devices sufficiently accurate and precise?” asks Hall. “I don’t think we know yet.”

Do CGMs help with weight loss?

“Certain foods can cause your glucose to spike beyond your current energy needs,” says Signos. “Your body then converts this excess glucose into fat.”

But there’s no good evidence that people gain more—or lose less—weight if a meal causes a spike in glucose.

“We saw much lower glucose levels on CGMs after meals when we fed people a low-carbohydrate diet as compared to a high-carbohydrate diet,” says Hall.

“But these differences in CGM glucose didn’t translate to the predicted differences in body fat. In fact, people lost more body fat on the diet that produced the greatest glucose spikes.”

The bottom line

CGMs can help people with diabetes control their blood sugar. But there’s no good evidence that CGMs help people lose weight.