Fermented Foods and The New Gut Science, by Tim Spector

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A food scientist unscrews the lid on astonishing new research that suggests everybody should be eating three portions of fermented food a day.

Yesterday’s London Sunday Times carried a long article by fermentation expert Tim Spector. In Tim Spector’s fermented food diet — and the new gut science the King’s College, London, professor, and co-founder of ZOE, and author of the forthcoming book Ferment. In it, he detailed the many benefits of a diet rich in fermented foods and beverages such as kombucha.

Spector’s article makes the following points.

Groundbreaking Research Results: His 2024 study of nearly 10,000 UK volunteers found that eating three portions of fermented foods daily for three weeks led to remarkable improvements: 47% saw better mood, 55% had more energy, 52% experienced less hunger, and 42% had reduced bloating.

Personal Fermentation Journey: Spector became a fermented food convert, making his own kombucha, creating “Timchi” from leftovers, and incorporating fermented vegetables into nearly every meal. He now considers regular fermenting essential for both happiness and health.

Understanding Fermentation: Fermentation is the chemical transformation of food using yeast, bacteria, or other microbes, creating hundreds of new compounds. This ancient preservation method makes foods infinitely more complex in flavor and nutrients than their raw forms, like wine versus grape juice.

We now know this ancient process of alchemy not only transforms the flavour of the food, making it more complex, varied and delicious, but it also brings a multitude of additional health benefits.

Fermentation vs. Pickling: Many people confuse fermentation with pickling. True fermented foods use brine and beneficial microbes, while pickled foods use vinegar for preservation. Fermented foods like sauerkraut offer superior health benefits and more complex flavors than their commercially mass-produced pickled counterparts.

Three Types of Beneficial Compounds: Fermented foods contain probiotics (live beneficial microbes), prebiotics (food for gut bacteria), and postbiotics (dead microbes and their byproducts). Each type provides specific health benefits, with fermented foods offering a broader range of microbes than most supplements.

The “Zombie Microbe” Discovery: Recent research reveals that even dead microbes (postbiotics) provide health benefits through chemicals they produce or proteins on their cell walls. This means pasteurized, frozen, or heat-treated fermented foods can still offer therapeutic value, revolutionizing previous understanding.

We now believe postbiotics can provide health benefits through the chemicals they produce or from proteins on their cell lining. So far these zombie microbes only appear to be helpful, not harmful. Even mistreated microbes that have been neglected, overheated, pasteurized, frozen, starved or overfed on sugar can still provide some benefit.

Digestive and Immune Benefits: Fermented foods improve digestion by breaking food into smaller, more absorbable pieces while maintaining the crucial gut barrier. With 80% of immune cells lining the gut, fermented foods help regulate inflammation and may reduce severity of infections, including COVID-19 symptoms.

Balancing the Gut Microbiome: Microbial diversity is a crucial health indicator, with low diversity linked to depression, diabetes, allergies, autoimmune diseases, and poor cancer treatment response. Fermented foods improve microbiome health by preventing harmful bacterial overgrowth while encouraging beneficial species diversity.

Mental Health Connection: The gut-brain connection is more direct than previously understood. Gut microbes produce neurotransmitters like serotonin and dopamine, while gut immune cells can signal the brain about inflammation. Studies show fermented foods can improve mood as effectively as antidepressants in some cases.

Cancer and Energy Management: Fermented foods may help manage cancer risk by reducing chronic inflammation, allowing the immune system to better detect rogue cells. Regular consumption is linked to 20% lower cancer risk, particularly colon cancer, and can boost energy by reducing inflammatory fatigue.

Evolutionary Perspective: The gut’s complex nerve network, often called our “second brain,” may actually be our evolutionary first brain. Early multi-celled creatures like hydra developed as simple tubes with nerves around them, suggesting our gut deserves more respect as a primary communication center with the brain.

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4 Responses

  1. the_editor says:
    September 7, 2025 at 5:50 am

    A less than flattering review by Sarah Ditum was printed in the London Times newspaper on September 5, 2025.

    From kimchi to kombucha — what’s so great about fermented food?

    Tim Spector, the scientist turned health influencer, extols the virtues of fermentation — while flogging his own ‘Gut Shot’ of kefir

    Fermentation, Tim Spector writes, is the “ancient process of alchemy” by which microbes — mainly bacteria and fungi (including yeast) — transform one foodstuff into another, even more exciting one. Boring old milk turns into thrilling substances like yoghurt, kefir and cheese. Grapes become wine. Wine becomes vinegar. Tea becomes kombucha.

    This is all very delicious, if you like that sort of thing, which I do, even though “getting into ferments” is up there with wearing a Dryrobe in terms of middle-aged cringe. (And yes, I do have a Dryrobe, thank you.) But according to Spector, a professor of epidemiology at King’s College London and long-term advocate for the importance of the microbiome, the benefits run deeper.

    He cites one study of 10,000 volunteers who ate three portions of fermented food a day for three weeks — 47 per cent of them experienced improved mood, 55 per cent reported more energy, 52 per cent had less hunger and 42 per cent had a decrease in bloating. Spector declares this “amazing” and adds: “If these results had been for a new vitamin supplement it would be blockbuster.”

    His giddy tone makes it easy to miss the fact that these results do not sound, on a sober assessment, wildly impressive. It amounts to saying that if you give a certain population a certain intervention, there’s about a 50-50 chance they will tell you they feel better. That’s not nothing, but between the placebo effect and the vagaries of self-reporting, the claim in Ferment’s subtitle that these foods are “life-changing” might be an overstatement.

    It’s true that this is stronger evidence than exists for most vitamin supplements, but then most vitamin supplements show negligible effects except in cases of deficiency. Obviously, I still take my daily cocktail of zinc, iron and magnesium because I’m just that kind of person: the Dryrobe-wearing, kefir-glugging self-optimiser. The kind of person, in fact, who has helped to make Spector very rich.

    Because Spector has undergone his own process of alchemy. Go back a few decades and he was a normal — albeit very respected — academic. In 1992 he established TwinsUK at KCL, a vast registry of identical and non-identical twins for clinical research. This is hugely valuable in exploring the genetic and environmental causes of disease, and has contributed significant breakthroughs on cardiovascular disease, diabetes, obesity and osteoarthritis.

    Spector parlayed the twin studies into a series of successful books on health, particularly diet, and gained even greater prominence during the Covid pandemic as the public face of research into coronavirus symptoms. He’s one of the main reasons you’ve heard so much about the harms of ultraprocessed foods (UPFs); he’s also the source of the widely bandied advice about eating 30 different plants each week.

    In 2018 he fully embraced the world of entrepreneurship when he co-founded the company Zoe. This uses at-home testing (a glucose monitor, a pinprick blood sample and — look away if you’re squeamish — a poo sample) to develop a personalised nutrition programme. Subscribers pay £299 up front for the tests, then up to £24.99 a month. Zoe also conducts research, including that study on ferments that Spector found so compelling.

    There are other Zoe products you can buy. The Gut Shot is a small bottle of kefir costing £2 for 150ml, while Daily 30+ is a powder to “support your gut and energy” (£39 for a month’s supply). In May the Advertising Standards Authority banned an advert for Daily 30+, warning Zoe not to promote its products as UPF-free when some of the ingredients looked an awful lot like they had been ultra-processed.

    As the cabbage in the Kilner jar ferments to become kimchi, so the scientist in the biotech start-up gradually transforms into a health influencer. On the one hand, you would hope that Spector was happy to stand behind his own product. On the other, there’s an undeniable conflict of interest when a scientist’s research is directly tied to his commercial concerns.

    So while Spector writes like a popular scientist, the sharp tang of the businessman is always present. When he complains at length that “the regulation and promotion of gut-friendly foods is a mess”, I wonder if he’s thinking about that ASA judgment. In any case, he immediately goes on to praise his own Gut Shot, although not directly by name, as “the best available on the market”.

    Personally, I’m very open to the idea that fermented food is good for you, and tempted to try some of the recipes here. Nonetheless, it must be admitted that some of the research in this field is at best nascent. A nadir is reached in a passage on the potential benefits of pasteurised sake when Spector writes that “anecdotally a few Japanese mice having radiotherapy seem to have done well on it”. Who is reporting the anecdote? The mice?

    At other times, it’s less a case of TBC than TMI. Extolling the benefits of coffee (which, I was surprised to learn, is fermented in its progress from bean to cup), Spector tells us: “Many people (including my wife) find they can time their bowel movements to the minute after their morning cup of coffee; for me it is not so clear-cut.”

    But I suspect that for those who are fully indoctrinated into the cult of Zoe, an insight into their leader’s bowels will be scrutinised like a prophecy. I expect Ferment to sell by the palletload and lead to a mass infestation of mystery jam jars in the nation’s fridges. If it also leads to a rush on Gut Shots and Zoe memberships, well, that’s just what influencers like to call synergy.

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  2. the_editor says:
    September 7, 2025 at 6:10 am

    Clive Cookson reviews the book in the September 6 edition of the FInancial Times.

    Gut reactions
    Tim Spector explores the benefits of consuming fermented food that’s rich in bacteria.

    Gut guru Tim Spector has done more than anyone to popularise the microbiome, the trillions of beneficial bacteria that live inside us. Now he wants us to add a further multitude of microbes to our intestines by eating as much fermented food as we can. Spector’s scientific reputation rests on his pioneering studies of twins, launched at King’s College London in the 1990s, which started to unravel how genes and environment determine human health. He was struck by the huge influence of diet and then by the way different foods can change the composition of our microbiome — with profound effects on wellbeing.

    His earlier bestselling books ‘Spoon Fed’ and ‘Food for Life’ championed the benefits of varied plant-rich diets in nourishing a healthy diversity among the estimated 100tn microbes that inhabit a typical adult’s guts. Now with ‘Ferment’ Spector focuses on foods that can contribute their own cargo of friendly bacteria and yeasts.

    Spector practices what he preaches with the passion of a convert, aiming to consume at least three servings of fermented food per day — and making and storing most of them in his own kitchen. “Sorry about the state of the fridge,” he writes in dedicating the book to “my long-suffering wife”.

    ‘Ferment’ covers a range of foods and drinks generated by microbial action in converting sugars and other carbohydrates into other organic chemicals. But the book’s heroes are the four Ks: kefir, kombucha, kimchi and kraut. Two are drinks. Kefir, originally from the Caucasus Mountains, is fermented milk, more liquid than yoghurt. Kombucha, first made in China, is fermented sweet tea with added flavourings. Both are relatively palatable to the uninitiated.
    The other two are solid foods based on fermented cabbage: German sauerkraut and kimchi, its more complex cousin from Korea. Kimchi in particular, with its powerful garlicky aroma, is hard to love on first taste. Spector tells us it took him 10 years “to really get past the smell and into the flavours. But now I am totally hooked and can­not ima­gine how I lived without it for so long.”
    He is hooked on making as well as eating it, offering recipes for simple and traditional kimchi, “Kimchi Bloody Mary” and “Timchi” — his way of using up surplus vegetables by chopping them up, mixing with salt and submerging in brine in a Kilner jar with a self-burping valve to emit gas generated by fermentation. “It’s really very simple,” Spector says. “The microbes do all the work.”

    The book is studded with recipes. They appear within each chapter about an individual ferment and in a long section at the end of the book — too many for this reader who is unlikely to throw himself into fermentation, although I might try the recipe for honey-fermented garlic that Spector recommends as the simplest of all.

    One ferment is a long-standing fixture in my kitchen. A pot of red vinegar, started with a mother culture given by friends more than 20 years ago, flourishes with its liver-like microbial blobs fed periodically with leftover red wine. Curiously Spector advocates diluting wine with water to below 10 per cent alcohol to make homemade vinegar but mine loves full-bodied 13-14 per cent vintages — illustrating his point that fermentation is not an exact science.

    Fortunately those of us without the time or dedication to make their ferments can choose from an increasing range of good quality products sold in shops or online. They are brewed and bottled in a way that preserves a variety of microbes to interact amicably with our resident microbiome. I am becoming addicted to a commercial kombucha brand that Spector approves of.

    For a long time the clinical evidence about the effects of consuming ferments was lost among a plethora of small under-powered studies but now it is becoming clear, Spector writes.

    “The overriding message here is that whether you are male or female, old or young, overweight or not, you are highly likely to benefit from eating more ferments.”

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  3. the_editor says:
    September 17, 2025 at 10:16 pm

    Spector was featured in the Irish Times, September 17, 2025.

    Go with your gut: Scientist Tim Spector on the power of kefir, kombucha, krauts and kimchi
    Scientist Tim Spector on the power of kefir, kombucha, krauts and kimchi
    By Ella Walker

    When it comes to food, usually we’re told to cut the crisps, hold off on the biscuits, reduce the cake and watch our portion sizes. It feels much rarer to be told to load our plates up with more of something. But that’s exactly what epidemiologist and gut health expert Tim Spector is trying to get us to do, specifically with fermented foods.

    “It’s about eating more and putting more stuff on your plate,” says the 67-year-old, whose new book, Ferment, is a deep-dive on the super-good-for-you foods. “You like bangers and mash? Well, just add some sauerkraut to that and have a glass of kombucha with it. That will make it healthier.”

    Co-founder of personalised nutrition website, ZOE, Spector has been banging on about gut health for a decade, but for the past six years he’s gone all in on tangy, sour, addictive fermented foods, like kefir, kombucha, krauts and kimchi. Foods that, when he wrote his first book, The Diet Myth, “no one had heard of” and now “you can find them on every aisle”, proving that food culture can change fast.

    Spector aims to have something fermented with every meal, and says adding them to your diet is “far more important than any supplement you can buy”, as they support the immune system, help stop infection, reduce the speed of ageing, and even boost mental health. They’re also delicious. “We’ve evolved to have fermented foods and we’ve just forgotten,” says Spector, noting that being the country that started the industrial revolution is largely to blame – in many countries around the world, from Japan to much of Europe, fermented foods are still highly prized. “We just threw all the old traditional things out the window. We’re now back-pedalling,” he says, but it’s worth doing: “The most important thing we can do for our health is to make the right food choices.”

    Spector finds ferments so thrilling because “you eat your own science”, and the research involved is gripping too. “Things are moving so fast in this field, it’s just really exciting to see these products, which were seen as really alternative medicine, fringe stuff, are now going mainstream.”

    “People are doing proper clinical trials,” he continues. “Nobody calls you a nutter for even discussing it, which they would have done in the past.” One of the major new developments discussed in the book is the concept that healthy bugs in ferments “might work both alive and dead”. Which sounds alarming, but “means a lot of the products we thought were of no use actually could be of health benefit”.

    But where to start with eating them? “A lot of it is getting used to sour flavours again, because with all the highly processed foods we eat, full of artificial sweeteners and sugar, we’ve lost that love of sourness we had a few generations ago,” says London-born Spector, who helped develop the Covid symptom study app. You probably already have more ferments in your cupboard than you think though. Marmite is fermented, as is soy sauce and some tabascos.

    “You’ve got lots of things that were fermented in the process, like coffee and chocolate,” notes Spector. “Some yeasty beers pertain if they’ve got dregs at the bottom – they’re dead microbes you’re drinking that may be producing some mild benefits.” Yogurts that aren’t highly processed and Philadelphia cream cheese count too: “There are at least three different microbial species in that.” Cream cheese can also ease you into the more sour foods. Spector recommends mixing it with sauerkraut or kimchi so “you’re diluting that sharpness”, then move on to adding sauerkraut at the end of stews or soups, or “swap your stock cube for miso paste”.

    A more cost-effective, and entertaining option is making your own ferments. “I remember, 10 years ago, looking at people who made their own sourdough as slightly crazy, and now, my fridge is full of it,” says Spector. In fact, it’s half given over to ferments. “It’s full of little pots and bottles, either of finished ferments or of what we call little ‘fermenting hotels’ where grains and mothers and blobs are kept waiting for their next job,” he says. “My wife complains it’s a bit smelly when she opens it.”

    The idea of things bubbling away, having to check them and weigh them down, and the potential for explosions, often puts people off the idea. Admittedly, Spector has had the odd disaster himself, including a few kombuchas left too long, which, when opened, “the cork hit the roof, as did the liquid.” He also recommends “leaving off the turmeric until you’re really confident about doing this stuff”, unless you want to redecorate the kitchen yellow… There is an element of trial and error (Spector has only recently nailed fermented mushrooms), but the basics are straightforward to master, and the potential to learn and experiment, vast. You can’t get for simple the sauerkraut he promises, all it involves is cabbage, salt and time. “If you can learn to ferment something, you understand what happens to food inside your own body much more,” he says.

    “Fermented food should be part of everyone’s life, and we all need to know more about it. And whether you just buy it from the store or you’re inclined to try fermenting yourself, it doesn’t matter,” he says passionately. “This is an incredible gift that nature and evolution have given us, as well as being good for you, it’s incredibly tasty, there’s a whole new dimension in flavours. Once you’ve started, you won’t look back.”

    Reply
  4. the_editor says:
    November 14, 2025 at 5:11 pm

    A ZOE blog post elaborates on Tim Spector’s belief in the value of consuming fermented foods.

    Highlights:

    Tim uncovers why milk and cheese aren’t the same in your body — and the surprising science showing cheese might not be the villain it was once made out to be. He also shares emerging evidence that fermented foods could influence inflammation, immunity, metabolism, and even mood, often in a matter of weeks.

    In research from my book, the fermented product is nearly always healthier than the original product, and it’s probably because it contains more healthy chemicals and compounds.

    So you take cheese, for example. There’s no evidence that milk has particularly great benefits to adults because it’s quite two dimensional. It’s got sugar, it’s got protein, but when you get cheese, all the evidence suggests that regular cheese eaters have lower mortality, less heart disease risk, et cetera, which is rather strange because the initial products is the same.

    So it’s probably the microbes themselves changing the chemicals in that food. So they’re producing chemicals that are actually helpful for our bodies and those chemicals either acting directly on us or they’re affecting the other microbes in our ecosystem to then produce healthy chemicals. So I think complexity is generally better for us.

    That seems to be the general rule. And the same is true, eating just cabbage doesn’t seem to be as good as having fermented cabbage, which we call sauerkraut. Many other examples where the basic plant, just having. That plant is fine for you, but we seem to get extra benefit from perhaps the way the microbes have created all these extra chemicals and tastes and aroma.

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    So this is the problem of fermentation is, it has to stop at some point. And everyone who’s ever fermented will occasionally have something explode. And I’ve had a few occasions where bottles have come off rather unexpectedly, and again, upset my wife. But this is why when you scale up fermentation, manufacturers of things like kombucha have the same problem as the beer makers. They want to stop fermentation so you can put it in cans or bottles, so it’s no longer continuing to produce gas. So anything above 65 degrees will just about kill all these microbes.
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    Well, 10 years ago there were lots of little studies around the world, 10 or 20 people where they’d give them some fermented food and they’d see how they got on, but they didn’t stack up for me as a scientist of being really credible.

    And it’s only about three years ago that for me, it really switched. And there were a couple of studies that really convinced me this was more than just, oh yeah, this sounds a good thing to have, but I’m not sure how good it is.

    One was this study from Stanford, our colleagues, Christopher Gardner, you know well, and Justin Sonnenburg did a study where they had relatively small number of people, about 28 people, and they put them into two groups.

    One, having a high fiber diet. The other one having five portions of fermented food a day for around three or four weeks. And they basically taking nearly daily blood samples. So small study, but very intensive. And this hadn’t been done before.

    And in the blood samples, they were looking at all the immune proteins, so a whole batch of immunological studies at, at great detail and expense. And what they showed was that even after a couple of weeks, you saw a really significant drop in inflammation markers in the fermented food group.

    So not only did their microbiome change more than the high fiber group, but they had this dramatic decrease in inflammation markers. So it really helped the immune system. It changed 17 out of. 19 proteins they measured, so across the board, these were having a real effect on the immune system, and that’s probably the mechanism by which they are having this health effect.

    So the Stanford study for the first time showed in great detail that fermented foods can have a dramatic impact on the immune system as well as the gut microbiome. So to me, that was an eyeopener. And then put all the other studies into context. Those other studies had been the epidemiological ones, very population, big level, showing that people that had regular yogurts had regular cheese.

    Other fermented foods had lower rates of death, heart disease, better metabolic profiles. And some of these we’d done in our own studies at King’s using twins, which I was working on for 25 years.

    So, matching the big studies with these detailed ones and then all the little studies around the world with meta-analyses that had studied like 10 or 20 people with a few inflammatory markers all showed the same thing. So you’re putting all this together makes absolutely clear that these foods, if you have them regularly, small amounts regularly, will have a significant impact on your immune system and your gut microbiome. We should be learning from our ancestors.

    We should be learning from the latest science. We should all be having at least three portions a day.
    .
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    So you’re saying that in just in two weeks when I saw those data, that was a real wow factor. And it just showed you that if we can get just the people listening to this podcast spread the word that this is a normal thing to do, eating three ferments a day, we can all, not only improve our inflammation levels at the sort of local level, but actually this can affect our brain, our mental health, in the majority of people taking it in just a few weeks.

    This can have an incredible public health effect, and I just don’t think we, we’ve realized up to now that the huge potential of these fermented foods,

    Jonathan Wolf: You started by saying that you thought it was really good for our inflammation and reducing it. Now you’re talking about this study that you did with thousands of people through ZOE, and now you’re talking about things like mood and energy and hunger and constipation, which seems completely different.

    Tim Spector: Yes. What the Stanford study, going back to that one showed clearly improvement in immune health and you also got to shift in your gut microbiome towards a healthier looking microbiome. The two things are linked, and we know that inflammation is key to many features in the body and your gut health as well.

    So if you reduce inflammation, your gut health will also improve. So that would probably explain improving constipation. The mental effects of this, the improvement in mood and energy and hunger are probably through the effects of these microbes on the immune system.

    We think that they directly interacting with the immune system, whether they’re dead or alive through most of our immune cells, which are actually lining our gut. And they’re sending those signals. We dunno exactly how they do it, but they’re sending clear signals to the immune system.

    So all is well that gets transferred to the brain through the vagus nerve and other other mechanisms calming the brain down, reducing so-called neuroinflammation that helps our mood, that helps our concentration, that helps reduce fatigue. So this immune system linked with the gut microbiome is, is the key to really how we feel most of the time and a lot of our problems with modern illnesses due to the fact that our levels of INF of inflammation are much too high.
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    So usually people won’t like it the first time. It’s a bit like toddlers with some new food. You’ve got to keep going at it, introducing it, doing it in a mild way, and then start thinking about other drinks you can have. So, kombucha, the first ones might be a bit sour, but there’s some nice fruit ones to start on and you can wean yourself off the sweetness or the artificial sweeteners, just get used to those flavors. .
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    This is a scoby, which is a kombucha mother. Okay. So this is made by the microbes. It’s like a shell. They produce themselves. So there’s about 50 different microbes in here.

    Jonathan Wolf: Living inside that sort of jellyfish thing.

    Tim Spector: Yeah, they live inside there and they produce it for themselves. It’s like a little protective shell that they live in. So this allows ’em to live for years. I’ve had this for about 10 years. This one, it has babies and I give it to special friends.

    Jonathan Wolf: I’ve note that I’ve never been in a special enough friend to get given your Yeah, baby scoby. But on the other hand, it looks disgusting.

    Tim Spector: It looks disgusting, but when you add it to sugary tea, so you make a big pot of sugary tea, you just add that to it, leave it for a week, you’ll get kombucha and a completely different flavor. And again, once you’ve got this sorted out, it is actually much easier than it looks.

    Jonathan Wolf: And that goes from sugary tea. And we know anything that’s just full sugar is not healthy for you.

    Tim Spector: To kombucha which is a sour complex. Some say it’s the closest you can get to beer and it’s good for me and it’s very good for you. Yes, lots of studies show it reduces blood pressure, helps your blood sugar level, all kinds of benefits.

    So again, having this in the house, drinks of kombucha, but buy it in the stores first to see if you know what it, what it should taste like. But you, you can, this is incredibly cheap and easy to make.

    Jonathan Wolf: And so that, I guess is a brilliant example of the magic of these bacteria moving something really terrible like water and sugar on one hand into something that’s suddenly is actually healthy for me.

    Tim Spector: Yeah, it actually produces a bit of alcohol as well, usually below 1%, so you can’t feel it, but it just giving you an idea of what these microbes are doing. There’s yeast in there and they make CO2 and alcohol, so it’s very complicated.

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