Blood glucose meters are not necessary for people who do not have diabetes and in some cases can lead to an increase in eating disorders, leading doctors have warned.
It’s part of a diet promoted on social media and led by companies including Zoe.
But the NHS’s national diabetes advisor, Professor Partha Carr, said there was no strong evidence that the devices helped people who did not have high blood sugar levels.
In people with diabetes, blood sugar – also known as blood glucose – can remain high for several hours after eating. At very high levels, it can cause organ damage if not monitored and checked.
Zoe, which was previously involved in the coronavirus symptom tracking app, is one of the main companies selling blood sugar monitors for people who do not have high blood sugar.
It now offers a program that starts at about $380 and is advertised on social media platforms.
Participants log their food intake and wear a glucose monitor (CGM) for two weeks to measure blood sugar levels after eating.
In separate tests, their responses to fats and their gut bacteria were also tested.
Zoe says all of these tests helped her determine that even two healthy people can have very different responses to the same food — for example, one person’s blood sugar may rise and fall more after eating carbohydrates than another person’s.
But other researchers say what these numbers mean, if anything, including greater rises and falls in blood sugar in non-diabetics, remains poorly understood.
Dr. Nicola Guess, a nutritionist and diabetes researcher at the University of Oxford, said that the majority of evidence linking high blood sugar and its extreme diversity to health problems is based on glucose levels that only appear in diabetics.
She explains that high blood sugar is a symptom of diabetes, not a direct cause.
Type 1 diabetes occurs when the pancreas stops producing insulin, so regular injections are needed.
Type 2 diabetes is more common and occurs when the body’s cells become resistant to insulin, so more insulin is needed to keep blood glucose levels within the normal range. It can usually be controlled through diet, exercise, and close monitoring.
Zoe points to some evidence — including some very small studies — that even before blood sugar reaches prediabetic or prediabetic levels, high blood sugar and large changes during the day may be associated with some worse outcomes.
She says she’s been studying gut bacteria and is starting to see connections between gut microbes, diet, and health.
James Kinross, a gut microbiome expert and colorectal surgeon at Imperial College London, said that although the microbiome is hugely important, direct-to-consumer testing was “problematic” because “this is new science and there are many unanswered questions about how it works.” The microbiome and how it affects our health.
Dr Sarah Berry, lead researcher at Zoe, told the BBC that her program used “decades” of existing nutrition research, and their own studies into the links between blood sugar and health.
But she admits the company doesn’t have “all the evidence.”
But given the dangers of a poor diet, she said, “it would be irresponsible to wait decades to understand long-term outcomes such as heart disease and death.”
Dr. Ran Crook, a GP who founded a company that provides health services to startups, praised Zoe for trying to gather evidence, and said the lack of all the evidence about blood sugar should not be a “stifle of innovation.”
He and others, including some of Zoe’s critics, agree that CGMs can be a useful tool for some people to get motivated and change their diet.
However, people have been concerned about diet-related diseases for decades. Hundreds of diet programs have failed to solve the challenge of people clinging to bad habits when the environment they live in is full of high-sugar foods.
“Zoe is scientifically rigor in its approach, and is unparalleled in the industry in terms of clinical trials and robust research with a dedicated team of scientists and nutritionists looking to improve health with useful, evidence-based advice,” the company said.
But Dr Jess is concerned to see patients using Zoe products cutting out foods she believes are good for their health, because they appear to raise blood sugar.
This in itself can lead to health problems, and is not recommended by the company.
She adds that people who avoid carbohydrates will have a temporary “exaggerated glucose response” the next time they eat these foods, which she says is “perfectly normal,” but this may lead them to believe they are unable to tolerate carbohydrates at all.
Professor Carr believes that using continuous glucose monitoring devices – which diabetics use – when there is no health reason to do so, can lead to an obsessive focus on numbers which – in many cases – “can translate into eating disorders”.
According to the eating disorder charity Beat, “People with eating disorders often focus on numbers as part of their illness, so we would never recommend that anyone with an eating disorder use glucose monitoring devices.”
Zoe tries to screen people with a history of eating disorders, and Dr Perry told the BBC that staff at the company have access to nutrition coaches, who can support them with food anxiety, and advise them on treatment if they feel there is a problem.
The company published research based on the data it collected from participants to try to find specific patterns in areas such as food choices, hunger and blood test results, but it cannot show which aspects actually cause changes in health.
Zoe has conducted a study to understand the changes brought about by the programme, but it has not yet been published.
Zoe is a “comprehensive product that doesn’t just include microbiome testing or just continuous glucose monitoring,” Dr. Berry says.
However, Dr. Gies believes that since these elements are still unproven, without them, it is just a “scientific-sounding way to get people to eat more fruit and veg.”
She thinks much of Zoe’s advice, including eating more whole foods and less processed foods, is sensible, but believes this message is “not compelling enough” to sell a £300 product.
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