On 5 March 2024 the US Food and Drug Administration [cleared the first continuous glucose monitor](<https://www.fda.gov/news-events/press-announcements/fda-clears-first-over-counter-continuous-glucose-monitor>) that anyone could buy over the counter. Until then these sensors had been prescription devices, made mainly for people managing diabetes. The new one was meant for adults who do not use insulin, among them people without diabetes curious about how food and exercise move their blood sugar. In June of this year the agency [extended the clearance to children](<https://www.fda.gov/news-events/press-announcements/fda-clears-first-over-counter-continuous-glucose-monitor-children>) aged two and older who do not use insulin.

So an instrument of the sick passed into the hands of the well. As [Melissa Hogenboom reports for the BBC](<https://bbc.com/future/article/20261002-do-non-diabetics-need-to-measure-their-blood-sugar>), healthy people with no metabolic disease now wear devices that report their blood sugar through the day, while others have given up white bread and pasta altogether. Authors, podcasters and wellness influencers have spread the idea that everyone must hunt down blood sugar spikes and avoid them, on the theory that a healthy person who lets glucose surge is inviting hormonal imbalances, acne, mood swings and worse.

Now the specialists are answering back.

What the body does after bread

The mechanism is old and unremarkable. Carbohydrates and sugars, from refined sugar to fruit, are broken down during digestion into glucose, which passes into the blood. The level rises. The pancreas releases insulin, and the insulin moves the glucose out of the bloodstream and into the cells, where it becomes energy. Food is not even the only trigger: during hard exercise, says Jennifer Sherr, a paediatric endocrinologist at Yale School of Medicine in Connecticut, hormones such as adrenaline tell the liver to release more glucose to fuel the muscles, and blood sugar briefly climbs.

A rise is digestion working. It is not a failure.

“The biggest misconception is that every glucose spike is harmful,” says Adrian Brown, associate professor in nutrition and dietetics at University College London. Blood sugar usually peaks about an hour after a meal and tends to settle back to baseline over the following two hours. In someone whose metabolism is normal, Brown says, a short spike is no cause for concern.

Where the danger begins

Diabetes is another country. There the body makes too little insulin, or the insulin stops working properly, a condition called insulin resistance, and blood sugar after a meal can climb to dangerous heights. These patients must manage diet and exercise carefully and monitor their levels, and some take insulin or metformin.

The warning sign, Sherr says, is not the rise but its persistence: glucose that stays high longer than it should may mean the body is not regulating it normally. That can point to insulin resistance, which can develop after long exposure to high blood sugar and can lead on to prediabetes and type 2 diabetes. The persistently high glucose some diabetics live with can then damage nerves and eyes and bring heart disease and stroke.

Even this chain is disputed. Nicola Guess, a dietitian and senior research fellow at the University of Oxford, points to the lack of evidence that excess blood glucose directly causes insulin resistance. The likelier culprit, she suggests, is simpler: calories eaten beyond the body’s needs tend to be turned into fat, and the weight gained is itself a risk factor for type 2 diabetes.

The verdict of the sensor

For people with diabetes the continuous monitor is a serious tool. For everyone else the evidence is thin. Critics warn the devices can “prompt harmful dietary changes and distort perception of health”, not least because they can overestimate blood sugar. In a review, Brown and colleagues reported “a lack of consistent, high-quality evidence showing that CGMs improve health outcomes in people who do not have diabetes.”

A [2024 narrative review he led in Diabetic Medicine](<https://onlinelibrary.wiley.com/doi/10.1111/dme.15369>) searched the literature from 1980 to 2023 and found 25 relevant studies. It concluded that what counts as a normal glucose level differs between people, and within the same person at different times, and that accuracy differs between monitor models. When UCL announced the findings, its press release [called for more regulation](<https://www.eurekalert.org/news-releases/1049354>) of the devices’ use by people without diabetes, warning that anxious users might misread their data, shun foods for no reason, and in some cases drift toward eating disorders such as orthorexia.

Here a reflection, and only that: a number, once it can be read every few minutes, begins to look like a command. The person under the sensor ends up taking orders from a figure that, as the review found, nobody has firmly defined. The question of who decides what counts as a normal number is older than the device.

There may be one exception. Sherr says emerging research suggests glucose trackers could help identify people at higher risk of type 2 diabetes, though more evidence is needed before anyone can say the monitors actually benefit that group.

The ordinary plate

None of this makes a steadier blood sugar worthless. A sharp drop in glucose after eating can sharpen hunger and push total energy intake higher. Eating protein and vegetables before carbohydrates has been found to blunt the rise that follows a starchy meal. Meals combining protein, fibre-rich plant foods and healthy fats slow digestion, release energy more evenly and help keep weight in check.

Bodies also refuse uniformity. “There is considerable variation between individuals, and the same person may show different responses depending on factors such as sleep, stress, activity levels and the type of meal consumed,” Brown says.

Cutting out carbohydrates, as some diets urge, can backfire, Guess warns: a carbohydrate-rich meal eaten after a stretch of restriction can send blood sugar higher than usual. Carbohydrates are considered an essential part of a balanced diet, and in a recent review Guess notes that excluding whole food groups can mean giving up foods that do people good.

Whether healthy people gain anything from glucose monitoring is still undecided. What is already known is that most people eat too much added sugar, and cutting that down needs no device on the arm.