November 20, 2023

Zoe’s Tim Spector on the rise of the UK’s fastest growing healthtech and becoming more than a 'diet app'

Tim Spector says the healthtech wants to “change the way people think about food forever” — but Zoe has its critics

Tim Spector, cofounder, Zoe

Unlike most startup founders, it’s hard for Tim Spector to walk down the street without people noticing him. 

Over the course of a career spanning nearly 40 years, he’s plied his trade as a doctor, author, scientist, entrepreneur and — more recently — diet influencer, with more than 500k followers on Instagram. 

Spector’s fame rocketed after his personalised nutrition startup Zoe, which launched in the UK in 2018 with gut microbiome testing and a diet tracking app, pivoted to allow members of the public to log Covid symptoms. At its height in 2021, Zoe’s Covid app had 4.7m users, and the study became the world’s biggest citizen science health project.


Since then, his social media following has ballooned — with users flocking to Spector’s short videos on topics from ultra-processed food alternatives to simple, healthy recipes. He’s also written a Sunday Times bestseller, appears in national UK press on the regular and keeps up his day job as professor of genetic epidemiology at King’s College London. 

“It’s been a crazy journey,” says Spector, a softly-spoken 65-year-old, who’s worked in disciplines as varied as rheumatology and epidemiology, twin studies and epigenetics. 

“I get bored when things are always the same,” he tells me, as we sit down for an interview at the dining room table of his North London home, a big jar of butternut squash fermenting in the background. “I could’ve stayed in my original area of rheumatology. But then I saw some of my colleagues who had been [researching] it for 20 years and thought ‘I can’t do that — this is really dull’.”

How Zoe works

At Zoe — the UK’s fastest growing healthtech by headcount — things move with more pace. The six-year-old company now has more than 400 employees, according to LinkedIn. Its lofty ambition is to “change the way people think about food forever”. 

For Zoe users — including this reporter — that begins with attaching a glucose monitor to your arm for two weeks, collecting a stool and blood sample and eating five specially designed muffins across breakfast and lunch on a single day. (This allows Zoe to compare your blood fat and sugar responses to thousands of other users.)

Four to six weeks later your results are emailed to you. Thousands of foods are rated out of 100, based on the impact they have on your blood sugar, blood fat and gut microbiome. Sausages (unsurprisingly) scored poorly for me (and presumably everyone else) with 8. Kidney beans, sunflower seeds and cucumber scored 100. 

The idea is that by incorporating more of those high-scoring foods into your diet, users will experience a number of health benefits like better sleep and improved energy levels, and avoid chronic health issues.

Zoe sells testing kits for £300 and an ongoing monthly subscription to an app, which costs between £25 and £60 a month (depending on how long a user subscribes). On the app customers can also log meals, get recipes and access short nutrition lessons. 

It’s certainly not cheap — but Zoe’s growth has skyrocketed since launching its testing kits in the UK in April 2022. More than 100k people — including TV presenter Davina McCall and podcaster Steven Barlett (who also invested in Zoe this year) — have taken part in the Zoe programme. 

Commercialising science

When cofounders Jonathan Wolf and George Hadjigeorgiou pitched the business idea to Spector after a talk he was giving at King’s in 2017, he wasn’t convinced. 


“I knew we could do some great science, but I wasn’t sure we could translate great science into a viral product. I didn’t expect to see them again after our initial talk, where I said ‘I want to do science, and it’s going to be expensive’.”

Spector says he thought it would be hard to get funding for a project that would take years to turn a profit (Zoe made a loss of £9m in 2021-2022, according to its most recent financial report). 

But, in actual fact, raising money has been “easy” — unlike his two previous ventures (a biotech startup in the late 90s and a gut microbiome startup just before Zoe). “Investors saw a team of two experienced business people who’d done this before, with a credible scientist with these ideas that were in the news.” 

Zoe has picked up $101m — from VCs like Balderton, Ahren and Daphni — since spinning out from King’s in 2017. It’s got the company to a point where it doesn’t need to raise again, Spector tells me — before quickly adding “never say never”.

Zoe is part of a small but growing wave of direct-to-consumer health testing startups — covering everything from blood to hormone and fertility testing — that have begun to entice VCs over the past few years. 

While Zoe is the clear frontrunner in the consumer gut microbiome testing field in Europe, in the US there’s also Viome — which has raised $186m since launching in 2016, and Sun Genomics — which has picked up $11.6m since launching the same year.

The startup also launched in the US, but is now solely focused on growing its UK base to take advantage of the huge following brought in by its Covid app. 

Does Zoe work?

The science behind Zoe is based on Spector’s PREDICT programme — an ongoing research project he leads at King’s, along with Massachusetts General Hospital, Stanford Medicine and Harvard T.H. Chan School of Public Health. 

It has analysed things like blood glucose and fat levels, activity, inflammation, sleep and gut microbiome diversity of more than 6,000 people since starting out in 2018 — and says is the largest research programme of its kind in the world. Zoe has used the project’s analysis of people’s bodies and food intake to predict users’ individual response to certain foods. 

The majority of nearly 5,000 reviews on customer feedback site Trustpilot are positive, with users reporting better dietary habits and a number of health benefits like weight loss. According to an internal survey Zoe carried out with 450 people who did the programme for 12 weeks, 70% said they had more energy and 85% said they had improved their gut health.

Results from a randomised control study (announced last week, but yet to be peer-reviewed or published) comparing several health markers of a group of people with access to the Zoe app and another being given US-government dietary advice, also found that participants on the Zoe programme showed more improvement on waist circumference, weight, blood fat markers and gut microbiome composition. 

But not everyone is convinced. 

Because the internal survey results aren’t based on a control group — where two groups of subjects are given different diet plans — they’re “clinically pretty meaningless,” says Dr. James Kinross, a consultant colorectal surgeon at Imperial College London. 

“[Energy and gut health] are subjective descriptions. They are completely non-specific and unhelpful outcome measures — it’s marketing.”

While Zoe says the survey still represents “real change for the participants”, Kinross isn’t alone in his scepticism. 

Mona Bajaj-Elliot, an associate professor at University College London, tells Sifted that gut microbiome science just isn’t understood well enough yet to be able to conclusively say that products like the Zoe programme will lead to better health outcomes than a balanced diet.

Some critics also point to the fact that the randomised control research wasn’t done under the conditions of a blind study — where participants don’t know which group they’re in — making the results less reliable.

But Zoe says that​ "as with most nutrition interventions, it’s difficult and often impossible to blind participants to which intervention they are receiving. This does not make the trial less valid as it’s a dietary programme, not a narrow pharmaceutical product."

Kinross also has concerns about patients with diagnosed illnesses drawing unhelpful conclusions from the Zoe app.

“A lot of my patients turn up at my clinic with Zoe test results, and I spend a lot of my time explaining to them why Zoe is not helpful and why they’ve wasted their money,” Kinross says. “You have to be very careful about how you're actually applying [the PREDICT research] in practice — because, basically, it has no real relevance [in a clinical setting for people with diagnosed illnesses].”

Zoe tells Sifted it’s “not designed as a medical device or diagnostic tool and is not appropriate for people with an ongoing diagnosed illness. We are clear in our messaging with our members that Zoe is a tool in adjunct to medical advice, not a replacement for it."

Making money from scientific research

Spector gets criticism “from everywhere”, he tells me — although rarely to his face. “There’s a lot of jealousy in academia. You can be criticised for being too much in the media and for being too commercial and wanting to make money.” 

He says combining academia with business does come with potential conflicts, though. “But, if in selling the product you’re getting the message out to a wider group of people that can’t afford it, who are then going half the way to doing it, it resolves that conflict in a way.” 

Whether that message really is getting out to the masses remains to be seen. 

Spector says the Zoe podcast provides nutritional advice for free to a wider audience. But Kinross tells Sifted that charging hundreds of pounds for a testing kit and subscription means Zoe is only available to the middle class and wealthy — and “isn’t going to solve the nutrition and diet crisis and obesity pandemic”.

That clearly isn’t quite Zoe’s goal at the moment though. Right now, the big challenge for the startup is working out how to convince users to pay for the product for longer.

Spector reels off plans to launch a number of products, like personalised prebiotics and meal kits and retesting at regular intervals in the future. The focus is targeting the “half” of users that only use Zoe for six to nine months before leaving, he says. “The idea is: how do we keep people for years?” How can it be more than “a diet app”? 

It will also launch gut microbiome retesting in the coming weeks, to encourage people to redo the test every six months to two years. “This could be a thing that people do for the rest of their lives.”

Longer term, Zoe has plans to relaunch in the US, and Europe after that, Spector says.

Working at Zoe

They’re all plans Spector will be heavily involved in, he says. “Reputationally, everything we do is science based, and ultimately that comes down to me.” 

Zoe is doing a “huge amount of press” at the moment, which means more interviews and TV appearances for Spector, who is currently also writing a sixth book alongside his research work. 

The schedule can be difficult to manage, he says, “I try to make things all go in the same direction.”

But it’s not been a totally seamless transition from scientist to founder for Spector — who says he’s “useless” at the hiring side of running a startup.

“I find the personnel stuff [difficult], and I found that in academia too — that’s the bit I really hated. I don’t have the patience to do three or four interviews — I just want to get on with it.”

Just getting on with it isn’t always straightforward, though. 

“I might want to do something that I think is really cool science, but it doesn’t quite tick all the boxes,” he adds — like an idea he had to build a feature in the app to assign each food a sustainability score. It was pushed back to make way for other features the Zoe leadership team thought would make more commercial sense to focus on. 

“It’s a mark of frustration,” says Spector. “Each meeting I keep mentioning it — it will come eventually.”

Photo finish

As our interview runs slightly over the hour mark I can see Spector beginning to look distracted. I ask him where the best place for a photo would be and he leads me outside to a long walled garden.

“I don’t know what a business photo is supposed to look like”, Spector says after a couple of slightly glum looking snaps. Smiling’s always good, I assure him, and take a few warmer-looking shots. 

We head back inside and the entrepreneurial spirit that’s seen Spector launch three businesses from his academic work comes back to the fore. 

“Do mention the podcast in the article,” he says — before running through the listening figures and telling me it’s the top branded podcast in the world. “It’s a pretty good marketing tool.”

Zoe provided Sifted complimentary access to the Zoe programme.

Kai Nicol-Schwarz

Kai Nicol-Schwarz is a reporter at Sifted. He covers UK tech and healthtech, and can be found on X and LinkedIn