“Your body is unique, so is the food you need.” This is the central credo of personalized nutrition (PN), as professed by its leading UK advocate, health science company Zoe. Since its launch in April 2022, 130,000 people have signed up for the service – at one point it had a waiting list of 250,000 – which uses a pinprick blood test, stool sample and a wearable continuous glucose monitor (CGM) to “eat smarter ” introduce. choices for your body”.
Like other companies operating in this space, Zoe has all the hallmarks of serious science. Its American equivalent Levels counts among his advisors many respected scientists, including Robert Lustig, known for sounding the alarm about the harm of refined carbohydrates such as sugar. Zoe is championed by King’s College London scientist Tim Spector, who claims she was “created with world-leading science”.
The problem with personalized nutrition is that it is still a young field of research, and there is not yet good enough evidence across the field to believe that we have yet found valuable new interventions that are more helpful than standard advice. Although a Food Standards Agency report last year said that “glucose monitoring and gut microbiome analysis could be more robust and feasible”. spoke for many experts when it was concluded that “the benefits of PN seem somewhat marginal compared to what is already understood about a healthy diet.”
One big problem is that personalization only goes so far, and a lot leans on a few key biomarkers. Take the use of CGMs. This allows wearers to see their blood glucose fluctuations and especially their post-meal spikes in near real time. Zoe’s theory was summarized by Spector: “If you have multiple spikes in a day, your average glucose level will be elevated. We know it increases your risk for diabetes and heart disease.” So if you can see which foods or meals produce the biggest spikes, the idea is that you can adjust your diet to flatter them.
However, most scientists remain unconvinced that non-diabetic users of CGMs can gain useful health information from them. “Glucose in someone without diabetes is a minuscule part of your overall metabolic health, let alone overall health,” says Nicola Guess, an academic dietitian and researcher at Oxford University who specializes in the dietary prevention and management of type 2 diabetes. diabetes. “There is a lot of inter-personal variation and one person may have more and bigger peaks than another but have the same average blood sugar level.” Doctors can accurately diagnose diabetes or pre-diabetes through a standard fasting or HbA1c blood test. In contrast, says Guess: “The data from a CGM does not have such diagnostic value” – something Zoe acknowledges.
Another problem is that personalized nutrition research bases much of its findings on analyzing mountains of data collected by its users. This brings up many associations between diet, blood glucose levels, weight and so on. But these “cross-sectional studies” can only find associations, not causation. The existence of a relationship between greater increases and higher average blood glucose levels, even in healthy people, therefore says nothing about causation. The higher elevations may be a result of an underlying metabolic problem, not the cause of one. If that were the case, keeping the nails would be addressing a sign of a problem, not its cause.
Worse, in very large data sets, Guess explains, cross-sectional studies will inevitably generate false positives: associations that are statistically significant but in effect random, “such as buying an iPhone on a Tuesday is associated with the risk of Crohn’s “.
Given these scientific limitations, says Shivani Misra, a diabetes researcher and consultant at Imperial College London, she sees no evidence for the theory that healthy people should aim to flatten their blood glucose curves. She rejects what she calls the “glucose-centricity” encouraged by CGMs, which she sees as “so one-sidedly focused on one metric of metabolism” when there are “so many other inputs that we can’t capture”. “I think people focus on glucose as a marker simply because we have technology to measure it,” Guess says. Personalized nutrition often starts with what it can measure, not what is most important to our health.
TThe usefulness of stool analysis is also questionable. Again, the basic premise behind the test is reasonable. Even James Kinross, a reader in colorectal surgery at Imperial College London, agrees that “the microbiome is highly individualized, and it is probably the most important determinant of our response to different disease risks or to different drugs.” However, along with many other experts, he believes that we still don’t know enough about what a healthy microbiome looks like. The best advice for nurturing a healthy gut microbiome remains to eat plenty of whole foods, especially fibrous plants, and to reduce your intake of broad-spectrum antibiotics.
More importantly, there is simply no such thing as good and bad bacteria, period. A bacterium can do good in one person and bad in another. Take the example of Escherichia coli, found in most intestines. It is a species with a lot of variation. Jacques Ravel, professor of microbiology and immunology at the University of Maryland, explains: “There are a few E coli that will give you major diarrhea, and there are some that are essential to your well-being.” Such a test for it lacks clinical validity, meaning that “there is absolutely no clear way of telling how it relates to health or ill-health”.
Moreover, Ravel has published a paper detailing several studies questioning the accuracy of stool testing labs – some of which could not reliably identify the bacteria in the gut, with certain labs in a US study produce different results for the same sample.
“My view is that Zoe personifies things that don’t matter,” says Guess. “The things that kill people in the UK and worldwide are LDL cholesterol and blood pressure.” Data, she notes, that Zoe doesn’t measure.
A key barrier to personalized nutrition is that in the scientific health world you can do cutting edge research or you can give established advice, but it’s challenging to do both. Companies like Zoe try to ride both horses at once. On the one hand, Zoe is a research project, in the continuous process of analyzing its users’ data and looking for new insights. On the other hand, it already advises users based on its work in progress.
Sarah Berry, an associate professor at King’s College London and Zoe’s chief scientist, bite this spot. Of Zoe’s science, she admits that “it’s fair to say it’s controversial and it’s contested”, but that’s because “anything that comes out is always more controversial”. Yet she justifies Zoe running “ahead of the curve” on the basis that “if we wait until we have how many RCTs [randomised control trials] and this causal relationship beyond all doubt, I don’t think we will ever progress to a point of being able to give people actionable advice”.
Misra says she doesn’t buy it. “There are well-designed studies that are gamechangers, that actually change outcomes for people in a compelling way and that are cost-effective and change policy. I can give you numerous examples.” One of them is the research on low-calorie diets, which are intended to push type 2 diabetes into remission. “It was a randomized controlled trial, a very high-impact study. Within three years of that finding, it’s now a national policyand everyone can access the remission program.”
Zoe also blurs another important distinction. Healthcare providers are subject to a number of onerous legal restrictions. But Zoe currently operates as a wellness company, which, as Ravel says, runs “without the regulation that applies to clinical and medical operations”. Hence the disclaimer on the front of the Insights report, sent to everyone who completes Zoe’s two weeks of monitoring, which warns: “Your insights are not clinical test results… Before making any changes to your diet, please consult your doctor.”
Yet the entire program is designed to drive dietary change, to gamify eating so that users try to achieve a Zoe score of more than 75 out of 100 for their daily food intake. Its marketing is littered with health claims, with its homepage urging people to “eat for your body and health”, listing benefits such as “Improved gut health”, “Achieve healthy weight” and “Improve overall health”.
Wwhen I asked Berry about this tension between giving very clear advice and yet denying such a thing, she said she would have to get back to me. Despite the push for this, no such explanation was forthcoming. “Why aren’t the regulators interested in this anymore?” Kinross asked. “I don’t get it for the life of me.”
Yet Zoe claims it is “scientifically proven to work”. It relies on the publication of the first peer-reviewed study of his program this month. There were some positive but modest outcomes: an average weight loss of 2.46 kg is significant but not very impressive after more than four months. However, there were no changes in several other biomarkers, including blood pressure, insulin, glucose, and postprandial triglycerides.
More importantly, the study compared Zoe participants to a control group that was tested far from blind. They were simply given standard dietary advice and a helpline to call. It was entirely predictable that people who logged every meal with Zoe for 18 weeks would eat more healthily. The study group as a whole was also not representative of the general population: 86% were women and their average body mass index was 34 when anything over 30 is considered obese.
Guess has already posted a blog detailing criticisms of the study while Kinross says the trial seems “designed to create what I would call marketing science, which is just enough science that you can convince a layman that it has value”.
When challenged about the design of the experiment, Berry admitted “if we wanted to test the effectiveness of purely the Zoe scores, then we would have to match the method of delivery” so that both groups use the same app. This will allow a study “to look at how the actual advice itself compares to standard care advice delivered in the same way”. But while Berry says that would be fine, the actual study was designed to test “the effectiveness of the Zoe program” as a package, comparing it only to “standard care.” This seems like an odd goal: if Zoe’s USP is the personalization of the advice, why design a study that deliberately does not test those elements?
Meanwhile, consumers are actually paying personalized nutrition companies to have their bodies monitored to an extent Kinross finds “Orwellian.” Zoe requires a one-off payment of a penny short of £300 and a monthly subscription of £24.99. “People don’t understand the value of the data they’re paying to give away,” he says.
These are the issues when personalized nutrition is a research project—and people pay large sums to be its guinea pigs.
