Many people with diabetes (including Nick Jonas, who appeared in a Super Bowl ad for Dexcom’s CGM), more average Joes and Janes, and even elite athletes are shooting continuous glucose monitors into their arms in order to detail their levels throughout the day.

If you’ve seen a plastic circle on the upper back of a person’s arm, that’s a CGM. They’re the easiest way to track glucose. Blood sugar meters or glucometers require a small sample of blood to test—usually through a finger prick.

The hope is that CGMs will help people figure out the best foods to eat and the right order to eat them to encourage weight loss, increase energy, and make other health gains.

Understanding glucose levels

Blood glucose, which your body creates from food during the digestive process, provides energy. Insulin shuttles it through the blood system into cells, giving you the get-up-and-go to play tennis, hit the gym and, or get work done. Your body uses some immediately and leaves the rest in cells for use later.

Dr. Liz Applegate, distinguished senior lecturer and director of sports nutrition emerita at the University of California Davis, likens the body’s delivery system of blood glucose to the hallways of a multi-classroom kindergarten building. “Think of your body as a busy school. All your blood vessels are the hallways and the cells are the classrooms. Insulin is a hallway monitor and the students are blood glucose,” she says. “So when we have an influx of glucose students from what we’ve eaten, the insulin tells the glucose where to go. It knocks on the doors of the classrooms. If the cell receptor is working well, the door opens up and glucose goes in. That’s normally the situation.”

When it doesn’t work, that’s “hundreds of little kids running loose unsupervised and scribbling on the walls. That’s glucose damaging the epithelial lining of blood vessels” and creating health problems.

When blood glucose drops in diabetics, they become hypoglycemic and may start shaking, feel dizzy, become lethargic, or get very confused. Over time, uncontrolled diabetes can lead to heart or kidney disease and severe vision and auditory issues, as well as problems with the feet. So, yes, monitoring glucose is a must for this population—as well as for those with a family history of type 2 diabetes or other symptoms of pre-diabetes.

But for people who don’t have diabetes, blood sugar fluctuations aren’t usually dangerous. They’re, mostly, just part of everyday life as people eat (or skip meals), exercise, and drink alcohol.

“There are many many factors that impact it,” says Applegate. And blood glucose levels balance out as daily activity changes.

How continuous glucose monitors work

CGMS do not measure blood glucose levels. Instead, they measure levels of glucose in interstitial fluid, or the fluid surrounding your cells. Glucose usually flows from blood vessels into cells, so glucose levels in interstitial fluid often lag blood glucose levels a bit.

Most CGMs include a housing that contains a data transmitter and a minimally invasive filament sensor that’s shot under the skin. (Earlier versions—some of which are still on the market—used a needle instead of the filament.) The filament, which is coated in a glucose-sensing enzymes like glucose oxidase, wears out over time and must be replaced every seven to 14 days, depending on the brand. The housing is held in place with an adhesive on the back of the wearer’s arm. The data transmitter sends information collected through the filament to a monitor or an app on the user’s phone and, usually, whatever service the person is using to monitor their numbers. For diabetes patients, this can include a clinic or a doctor’s office.

For non-diabetes CGM users, the numbers are where things can get tricky. Blood sugar is a constantly shifting number, depending on what you eat and drink, sleep, exercise, stress, hormones, medications, time of day, and more. Diabetics know what to watch for but, for non-diabetics, the meaning behind the constantly shifting number can be confusing.

CGM technology

CGMs, whether for diabetics or people who are blood sugar curious, are not a cheap technology. Insurance or Medicare generally pay for a CGM for people with diabetes. But the technology is now also being produced for wellness-driven companies, rather than those sitting on the purely medical side of the glucose line.

Companies that offer CGMs to the general public—usually through direct to consumer sales—include NutriSense, Signos, and Veri. Their products are usually bundled with personalized nutrition advice based on the customer’s metrics.

At NutriSense, they say it’s a holistic approach to health that keeps future health problems from developing. “We’re spending more money per capita every single year on folks trying to help them with their health, and more than any other country in the world. People keep getting sicker and sicker,” says Dan Zavorotny, co-founder and COO of NutriSense, a company that provides everyday people with CGMs and offers personalized nutrition counseling based on the results.

He founded NutriSense to try and “prevent disease and give people information ahead of time versus trying to manage things when it was too late.”

The program, which has been on the market for over three years, costs $250 for a month of monitoring, and provides access to a dietitian who “helps you understand what you’re seeing, looks at your goals, and then tells you hey, I think these are the most important changes that you could make to improve your health,” says Carlee Hayes, senior nutrition manager at Nutrisense.

While the explanation sounds promising, there isn’t much research to back up glucose monitoring for the average person. “Historically, research is really lagging behind technology. Continuous glucose monitoring is no exception to that rule,” says Hayes.

But, she adds, there are “a lot of research studies right now using this technology in individuals without diabetes, but it’s really in that preliminary phase.” NutriSense is doing its own clinical trials and Zavorotny says “we’ve seen some really good results.” He couldn’t share details until the studies are published.

The cost of CGMs

Because of that $250 per month monitoring cost, CGMs are out of reach for a lot of consumers. The biggest cost comes from the hardware, which has to be replaced every two weeks because the sensors wear out, but Zavorotny says that “as it becomes more scalable and the hardware manufacturers start lowering the prices and there’s more competition in the marketplace,” the price will drop.

And, says Zavorotny, “theoretically insurance companies will start covering this over time [and] reduce the cost in the future.” He also says that people don’t need to wear the devices year-round. They say some customers use a CGM for a month to get baseline measurements and a first round of advice from their dietitians. (One month would require one swap-out of the hardware so the user can get a fresh sensor.)

Because these are not diabetic patients, day-to-day monitoring is not necessary. They can develop a plan based on a month of data. Then people return for another round of using the device every 12 to 18 months to adjust for where their life and eating is at that point. Customers only pay when actively using the devices and the service.

Should you use a continuous glucose monitor?

When it comes to using a CGM for general health, no physical harm comes from just using the devices.

Though Applegate doesn’t recommend the units for the average person, she thinks there may be some good use cases for elite athletes who want to get an edge before a big event. “But do you need to always have it?” she asks. “I look at it as TMI … especially for these average Joes who are doing it because it’s a fad and then they put it off to the side.”

Her recommendation? She suggests focusing on “gross measurements” like dropping 10 pounds or cutting three minutes from your 10K.