Trendy blood sugar trackers, such as those recommended by leading science professor Tim Spector's Zoe Diet, could cause anxiety and eating disorders, a British study suggests.

Diet companies offering blood sugar monitors could cause anxiety and eating disorders in healthy people, experts warned today.

Several companies, including the ZOE programme, founded by diet guru Professor Tim Spector, offer high-tech devices called continuous glucose monitors (CGMs). It tracks blood sugar levels through a patch placed on the customer's arm.

This sends information to a smartphone app that records the “blood sugar spikes” that occur when sugars from digested food enter the bloodstream.

On its website, Zoe claims that blood sugar spikes can lead to an increased risk of heart disease over time, and offers dietary suggestions to minimise this.

But several experts have questioned the research behind Zoe's claims, and other similar programs, saying they can cause anxiety and an unhealthy obsession with “pure food” among users.

The device, which is about the size of a £2 coin, sends updates on blood sugar levels to the user's mobile phone.

Blood glucose monitors have been used for years to help people with diabetes, a disease in which blood sugar levels get too high.

But a large-scale study by researchers from University College London (UCL) and Birmingham Children's Hospital found a lack of evidence to support the device's use in people without diabetes.

Dr Adrian Brown, lead author of the study and a nutritionist at University College London, said: “At the moment CGM can be sold by companies but has no medical use.”

“There is strong evidence that these drugs have transformed the lives of people with type 1 diabetes and have also had a positive effect on people with type 2 diabetes who are on insulin therapy.”

“But we don't have the same data for people who don't have diabetes.”

He added: “We're not saying CGM doesn't have merit, but at present there is limited evidence to support the claims made by private companies about its use in people other than those with diabetes.”

Dr Brown explained that what causes blood sugar spikes varies from person to person, individual to individual and device to device.

“The normal range for blood sugar levels in people without diabetes is around 3.8 to 7.8,” he says.

But the monitor could show a reading between 2.6 and 9.4, indicating possible hypo- or hyperglycemia despite the person's blood sugar levels being normal.

“This could potentially influence people to actually see normal blood sugar results and change their diet accordingly.”

Dr Brown said that even people without diabetes may experience a brief rise in blood sugar after eating, but that their levels are generally well controlled and often return to normal within an hour or two.

Although people with diabetes may experience long-term elevated blood glucose levels, which could put their long-term health at risk, short-term increases in blood glucose levels after meals are not associated with poorer long-term health.

“I think some of the advertising by CGM companies needs to be backed up with relevant evidence that's currently available,” he said.

“There are many anecdotal benefits reported by people who have used the companies.”

According to the latest UK data, around 4.3 million people had diabetes in 2021/22. A further 850,000 people have the condition but are completely unaware. This is worrying as untreated type 2 diabetes can lead to complications such as heart disease and stroke.

“But what's important is that companies adhere to the published data.”

Dr Brown also said there needed to be stronger regulation of the devices overall.

“This study found evidence that for non-diabetic people using CGM, it may cause anxiety about what normal blood sugar levels are and how this might affect their diet,” he said.

“This puts them at potential risk for developing eating disorders such as orthorexia (an unhealthy obsession with eating 'pure' foods).”

He also called for more independent research into CGM, given that most of the personalized nutrition data comes from industry-funded studies.

“Even the data on people with diabetes is largely industry funded, so more independent studies need to be carried out, separate from commercially funded studies,” he said.

A new study published in 2014 found that Diabetes medicationsreviewed 25 existing studies and warned that CGM is “becoming popular even among people without diabetes.”

The researchers said current “regulatory deficiencies” are encouraging the “off-label” distribution of CGM.

“We hope this will help avoid the continued risk of misinformation to people without diabetes and the 'off-label' exacerbation of health disparities.”

But Professor Spector said: “Tracking our health data is the future of health and personalised medicine.”

“Don't hesitate to monitor your blood pressure and how it changes. Tracking changes in blood sugar levels can be a powerful tool for prevention.”

“There are well-established benefits to the use of CGM in patients with diabetes and impaired glycemic response.

“Studies regarding its use in people without diabetes are ongoing and suggest it may be a useful approach, especially in settings where the burden of metabolic disease is increasing.”

“Our study, and that of other colleagues, shows the benefits of understanding postprandial and intraday changes in blood glucose levels.”

“We welcome further research on this topic to help us tailor advice to individuals and improve metabolic health. This is definitely the future.”

According to the charity Diabetes UK, an estimated 5.6 million Britons have diabetes, of which 1.2 million are undiagnosed.

For the past five years, the NHS has been offering people with diabetes CGM monitors to help them record their blood sugar levels instead of traditional finger-prick blood tests.

The device, which is about the size of a £2 coin, sends updates on blood glucose levels to the user's mobile phone.