Fermentation, as a concept, suffers from its own reputation. It sounds worthy. Technical. The sort of thing discussed by people who own multiple Kilner jars and refer to their fridge as though it were a living ecosystem. In lifestyle terms, it sits somewhere between sourdough evangelism and the faintly intimidating world of home kombucha.
Yet fermentation is also deeply ordinary. Entirely unglamorous. Older than most of the foods we now consider staples. Long before “gut health” became a supermarket slogan or a social media aesthetic, humans were quietly letting microbes get on with things.
“You take basic grapes and you make incredible vintage wine. You take cow’s milk and you make incredible cheese. Soybeans become miso,” Tim Spector, the scientist and co-founder of Zoe, tells Emilie Lavinia on The Independent’s Well Enough podcast. “Humans have been fermenting forever – it’s really in our DNA.”
For Spector, who has become one of Britain’s most recognisable voices on the microbiome, fermentation is neither fashionable nor fringe.
This framing is important because fermentation, in modern discourse, is often presented as an optional upgrade. A dietary flourish. Something layered onto an already balanced lifestyle by those with sufficient time, money or inclination. Spector argues almost the reverse – that fermented foods are not a novelty but a return to something evolutionarily familiar.
For years, probiotics were sold on a straightforward premise: consume live bacteria, populate the gut with beneficial microbes, reap the rewards. It is a neat story. Intuitively appealing. Scientifically, though, Spector argues, far too simplistic.
“We used to think it was just the live microbes that mattered,” he says. “We now know that’s highly unlikely. They’d be completely outnumbered by all the other microbes already in your gut.”
The gut, after all, is not an empty vessel waiting to be colonised but a densely populated environment. Introducing a few additional microbes, he suggests, is rather like releasing a handful of spectators into a stadium already filled with tens of thousands.
“What we think is happening is these microbes stimulate your immune system. They’re tickling it all the way down. That reduces inflammation, and that leads to all kinds of health benefits.”
Perhaps the most counterintuitive element of this evolving science concerns something that would once have been dismissed entirely: dead microbes. The logic of probiotic culture has long been dominated by viability. Live bacteria good; inactive bacteria pointless. Spector himself once subscribed to this view.
“I used to think everything dead was a waste of time,” he admits. “Now, it’s less clear. There is definitely some benefit from ‘dead’ microbes – what we call postbiotics.”
It sounds paradoxical – how can something biologically inert produce a physiological effect? “The microbes may not be alive, but their cell walls still interact with the immune system,” Spector explains. “They work a bit like vaccines – they still trigger beneficial responses.”
In practical terms, this complicates the tidy distinction between “live” and “non-live” fermented products. Shelf-stable foods once written off as nutritionally hollow may not be entirely devoid of value. Even so, Spector maintains a clear preference.
“Live ferments are still best because you’re getting both the live microbes and the dead ones together,” he says. “You’re essentially eating a mix of corpses and live organisms.”
If the science of fermentation has grown more nuanced, the consumer landscape surrounding it has become no less confusing. Supermarket shelves now groan under the weight of products promising digestive benefits, microbial balance and gut-friendly credentials. Spector’s view of these claims is, at best, sceptical.
“If you see a packet in a supermarket that says ‘gut-friendly’, beware. At the moment, all you need to do in the UK to make that claim is add calcium.” Nutritional labelling, he suggests, often operates according to regulatory technicalities rather than meaningful biological insight.
This is not limited to fortified snacks or functional drinks. Even seemingly straightforward categories, like pickles, conceal layers of ambiguity. The distinction between pickled and fermented foods is widely misunderstood, sometimes deliberately blurred. “Most pickles are made with commercial vinegar, which is basically acetic acid added chemically. There’s nothing really natural about that.”
True fermentation, by contrast, relies on microbial activity rather than acidic preservation. A salty brine creates conditions in which naturally occurring bacteria can flourish, producing acids, gases and the characteristic flavours associated with traditionally fermented foods.
The difference is not merely semantic. It shapes whether microbes are active participants or absent entirely.
Against this backdrop of marketing language and microbiological uncertainty, Spector’s advice is notably pragmatic. Take kefir, for instance, a drink that has become shorthand for gut-health sophistication but whose variations range from explosively alive to reassuringly bland. “If you open kefir and it froths up, you generally know that’s real.”
The presence of fizz and separation, often alarming to the uninitiated, signals microbial vitality. Yeasts and bacteria continue to metabolise sugars, generating carbon dioxide and altering texture. Yet Spector cautions against fetishising authenticity.
“I don’t think we should be too fussy,” he warns. “If it’s something you like and can have regularly, that’s more important than chasing some rare artisanal product.” Consistency, rather than perfection, is the governing principle.
The same logic applies to kombucha, another beverage whose artisanal origins sit uneasily alongside industrial scalability. “Scaling kombucha nationally is very difficult. Manufacturers use filtration, sweeteners and stabilising tricks simply to make shelf life workable.”
These interventions, he says, are not sinister but logistical. Live ferments are notoriously temperamental. Microbes continue to evolve, producing gases and altering flavour. Without control measures, distribution becomes commercially untenable.
For those deterred by price or complexity, Spector offers an almost mischievously simple solution: “If you have the time, it’s worth making your own. It’s virtually free.” The economics of fermentation, he argues, are often misunderstood. Far from being an expensive wellness indulgence, fermentation historically functioned as a preservation strategy and waste-reduction tool.
“Fermentation is actually a way of avoiding waste,” he says. “If you find half a cabbage in your fridge drawer, chop it, add 2 per cent salt, stick it in a jar… you’ve got sauerkraut.” The microbes, he notes, are already present. “The microbes are already there, waiting on the leaves. You just need to create the right conditions.”
Where Spector’s argument becomes most intriguing, however, is not in matters of digestion but cognition. The gut, long regarded primarily as a site of nutrient absorption, is increasingly understood as a biochemical and neurological actor in its own right.
“We’ve always assumed the brain is in charge of everything,” he explains. “That’s not true. The brain is just another organ responding to signals from the body.” Central to this reconceptualisation is the gut-brain axis – a bidirectional communication network linking intestinal microbes, immune responses and neural pathways.
“Gut microbes produce chemicals that influence the immune system, which in turn influences the brain. That affects mood, anxiety and behaviour.” The implications are both fascinating and unsettling. Psychological states, once framed almost exclusively in cognitive or emotional terms, may be partially shaped by microbial dynamics.
“You can take an anxious mouse, transplant its microbes into another mouse, and make that second mouse anxious.” Mood, in this account, is not solely an abstract mental phenomenon but a physiological state influenced by inflammation, signalling molecules and microbial metabolites.
“People don’t realise how directly diet can affect mood. They think food is just about calories.” This misconception, Spector suggests, helps sustain behavioural cycles that may inadvertently worsen wellbeing. “Comfort eating often does the exact opposite of comfort.”
Ultra-processed, low-fibre diets can disrupt microbial diversity, alter immune responses, and, in theory, influence brain function. The result may be a feedback loop in which emotional distress drives food choices that exacerbate underlying biological mechanisms. “Look at your diet before looking for a prescription,” Spector says simply.
Ultimately, Spector’s message resists the grandiosity that often infects nutritional discourse. There are no miracle ingredients, no singular superfoods. Instead, he returns repeatedly to a principle at once simple and demanding.
“If you want to feel well, look after your gut microbes.” How? Not through exotic powders or punishing regimes, but variety. “The simplest rule is diversity of plants. Aim for around 30 different plant foods a week.”
In a wellness culture frequently drawn to restriction, elimination and optimisation, the prescription is refreshingly expansive. Eat more things. Different things. Let microbes, those ancient culinary collaborators, quietly do the rest.
Listen to the full episode of ‘Well Enough’ with Tim Spector on Spotify and Apple Podcasts.