Personalized Nutrition Programs Are Making People Feel Weird About Food

Some doctors warn that personalized nutrition apps like Zoe can cause otherwise well patients an unhealthy amount of worry.
Woman placing a CGM  on their arm.
A CGM (continuous glucose monitor) from Zoe.Courtesy of ZOE

Chrissy Kinsella was looking for a more personalized approach to her health. “You know, what is good for you as an individual may not necessarily be good for the next person,” she says. So she reached for a subscription to Zoe—a personalized nutrition service cofounded by Tim Spector, a celebrity scientist and a genetic epidemiologist at King’s College London. Kinsella paid the £299 ($365) for a testing kit and later received a bright yellow package in the mail: a bundle of vials, patches, and muffins.

By testing, scoring, and monitoring how you respond to different foods, Zoe says, it can help with a whole host of problems. Its personalized recommendations can help you “reach a healthy weight,” “feel less bloated,” and “avoid chronic health issues,” claims its website. The program can even help with menopause, Zoe says.

But doctors are more ambivalent. Sure, getting people to think critically about what they eat can be beneficial, but scoring and monitoring someone’s diet could lead to unnecessary health concerns or even disordered eating. British doctors say they have seen perfectly healthy patients with concerns about their blood sugar control prompted by readings in their Zoe app.

A Zoe starter pack includes a fecal sampling kit, a finger-prick blood test, and a continuous glucose monitor (CGM). Participants are asked to take a blood sample before and after they eat a muffin precisely engineered by the startup to contain specific levels of fat, sugar, and proteins. Zoe then runs a blood-fat test to see how each person responds to fat in their diet (prolonged high levels of fat in the blood are a health risk). Combined with blood glucose data (from the CGM) and an analysis of the quality of their microbiome (via the fecal sample), these measurements are used to create personalized diet recommendations, where each item of food is scored on a scale up to 100.

A sugary food, for example, would have a low score for someone whose data shows their body doesn’t control blood sugar levels well; for someone with good sugar control, the same food would be scored a bit higher. Meals, too, are scored out of 100—based on the personalized scores of their ingredients, as well as how those ingredients interact.

Kinsella, who used the program for a year, says she values the insights it gave on what foods were more suited to her body—now she knows that she tolerates fat well, sugar not so much, and that dairy milk sits better with her than oat milk. Kinsella loved inspecting data about her body, but she admits she became obsessed with checking the app to see what her blood sugar was doing in response to what she ate, courtesy of the CGM.

Small, coin-shaped, and usually affixed to the upper arm, CGMs have been a regular appendage of people with diabetes for years now, allowing them to track dips and hikes in blood sugar without needing to prick their finger every time. There’s been a growing trend of companies selling the monitors to people without diabetes for them to track how their body responds to certain foods. Levels and Veri, two other personalized nutrition plans, also use CGMs.

Getting a score of at least 75 every day is the ultimate aim of the Zoe program. This figure is calculated based on what you’ve eaten. But Kinsella found herself ruling out a lot of foods because they wouldn’t get her to that magic number, and she thinks the app encourages this kind of obsessive behavior. “You’re giving people an app that is kind of almost gamified, in that when you hit this magical 75, you get a big green circle. And everybody wants to get 10 big green circles in a row,” she says.

Shivani Misra, a consultant doctor specializing in diabetes in London, has seen an influx of patients at her non-NHS practice who have either purchased a CGM themselves or through the Zoe program, and who’ve become worried they are at risk for developing diabetes—due to seeing either continuously high blood sugar levels or sharp rises and falls.

When Misra formally tests them for diabetes, the results always come back normal. “We shouldn’t be using CGM to diagnose diabetes; it’s absolutely not validated for that,” she says. What concerns Misra is the people she’s seen who are restricting calorie intake and have become extremely anxious about eating carbohydrates. “I really worry about that group, because they’ve just become overwhelmed with the data that they’re seeing, which is completely normal.”

“It’s set up to derive those kinds of behaviors in exactly the people that would be susceptible to it, in my opinion,” she says. The patients who came to her were seeking professional guidance because they felt their anxiety about what the data was telling them had become problematic—in the case of one patient, they felt they couldn’t eat fruit anymore. “I personally think there is some corporate responsibility to make sure that there is adequate safety in place for people,” says Misra.

Federica Amati, a medical scientist and nutritionist and a science communications strategist at Zoe, says that the company has “lots of systems in place for customer service, and for our coaching team to be able to flag if they feel that somebody is not interacting with the app in a healthy way,” she says. “Of course, the fact that there’s a score associated with food is still problematic if you have disordered eating.”

On the potential for programs like Zoe to burden health systems with concerned users, Amati says that the company is putting a task force together to investigate how medical professionals are experiencing Zoe’s influence. “We feel very responsible about it,” she says.

Nicola Guess, a dietitian and researcher at the University of Oxford, says that she has also been approached by patients concerned about their health after seeing their blood glucose spike while wearing a CGM offered as part of a personalized nutrition plan. When she tested these patients to assess their blood glucose control, their results were completely normal. “It’s just making them quite weird about food, and it takes a lot of the enjoyment out of food for no reason whatsoever,” says Guess.

But, says Amati, Zoe didn’t create the worried well, noting that the problem has been an issue for the public health service for a very long time. “For sure, we’ve probably now created a new stream for the worried well to feed into, but I think that that’s a bigger problem than just Zoe.”

There is also a big question mark over how useful personalized nutrition really is. Zoe’s nutrition scores are predicated on the idea that each of us responds to the same food in a slightly different way—thanks, in part, to our microbiomes. But translating this into dietary advice is trickier and less well understood. A personalized diet might tell someone to cut out white bread and eat more leafy vegetables, for example, but is this really more effective than the same advice delivered by a family doctor or a public health advertisement?

“Zoe doesn’t eschew all the normal health advice,” Amati says. “We’re not like, ‘Oh, no, don’t eat more fruits and vegetables’—it sits within the recommendations that we know are very good for the majority.”

There is precious little clinical trial data on personalized nutrition apps, says Duane Mellor, a dietitian and researcher at Aston University in the UK. One study from Israel published in 2015 compared personalized diets generated by a machine-learning algorithm with diets selected by a clinical dietitian. The authors found that people in both groups had fewer glucose spikes after meals—indicating a healthier diet.

But whether personalized nutritional plans really make a difference is something Zoe is studying. Next month, Amati says the company will be releasing the results of a randomized controlled trial, called the Zoe Method Study. The trial involved one group of people receiving the full Zoe product and another group simply receiving standard nutritional advice, plus access to support services through an app. The study aims to test the efficacy of a program like Zoe in improving cardiometabolic risk markers in otherwise healthy people, through testing their resulting levels of cholesterol and triglycerides (a type of fat), as well as measuring other things like weight, blood pressure, glycemic control, and hunger levels.

All of this doesn’t come cheap, and Zoe users have to pay membership fees for continued access to their bespoke scores. Prices start at £59.99 ($73) for a single month and go down to £24.99 ($30) per month for a year-long plan. At those prices, Zoe is aimed squarely at wealthier consumers—a point not lost on columnist James Greig, who wrote about Zoe in the newsletter Vittles.“If our environment really is saturated with poisons, then bespoke services like Zoe are not a scalable solution but a form of private health care that will further entrench existing inequalities,” Greig wrote.

Amati acknowledges that Zoe’s program is expensive, but she says, “The product at the moment is the price it is because the testing we do is expensive.” She says the idea is that, as the techniques and technology become more common, the price will come down accordingly, and that Zoe has plans to work with the NHS and other providers to “become part of the health approach.” In the meantime, the company places focus on communicating health advice for free through forums like social media and podcasts.

Zoe is still proving popular, with over 130,000 people having tried the service so far. Part of the appeal of personalized nutrition is that it goes beyond weight loss to address other concerns people have about their health. Zoe markets its diet as a way to improve energy levels, gut health, and sleep. William Viney, a researcher who has worked on personalized medicine, points out that there are a huge number of people who have health issues that aren’t easily addressed by doctors and mainstream diets. “They know that they’re not like everyone else, and they need to get to the bottom of something,” says Viney. “There is an opportunity to bring information, and with it care, to whoever can pay the price for such a product.”