Written and medically reviewed by Dr Zeeshan Afzal (MBBS) — Medical Doctor & Medical Content Lead, Welzo
Evidence-based · Honest about what's proven and what isn't · UK-focused
Last updated: July 2026 · Reading time: ~10 minutes
Bread is a fermented food. So are beer, coffee, chocolate and soy sauce. None of them contain a single living microbe by the time you consume them.
That's the confusion at the heart of this comparison: "fermented" describes how a food was made, not what's alive in it now. A great many foods marketed on their fermented credentials are microbiologically dead.
Table of contents
Fermented foods are the better everyday habit — and there is now decent human trial evidence that eating more of them increases microbial diversity, which is more than most supplements can claim.
Supplements are the better targeted tool. Named strain, known dose, matched to published research. No fermented food offers that.
But first, check the food is actually alive. Roughly half the foods people eat "for the probiotics" contain none.
This is the practical crux, and it's rarely spelled out.
| Usually contains live microbes | Fermented, but not alive |
|---|---|
| Live yoghurt Kefir (if not heat-treated) Raw sauerkraut — chilled aisle Raw kimchi — chilled aisle Unpasteurised kombucha Miso stirred in after cooking Some aged and raw-milk cheeses |
Bread — yeast killed by baking Beer and wine — filtered or pasteurised Coffee and chocolate — fermented, then roasted Shelf-stable sauerkraut and kimchi — pasteurised Soy sauce — usually pasteurised Tempeh — cooked before eating Miso boiled in soup — heat kills it |
The rule of thumb: live fermented foods are refrigerated, have a shorter shelf life, and say something like "live cultures" on the label. Anything shelf-stable at room temperature has almost certainly been heat-treated. See fermented foods.
Even when a food is alive, it still isn't a probiotic in the technical sense — and the distinction is formal rather than pedantic.
The International Scientific Association for Probiotics and Prebiotics published a consensus statement on fermented foods in 2021, defining them as foods made through desired microbial growth and enzymatic conversion of food components. The panel was explicit that fermented foods and probiotics are not the same category.
To qualify as a probiotic, an organism must be identified to strain level, present in adequate amounts, and shown to confer a health benefit. Live sauerkraut satisfies none of those: the organisms aren't characterised, the quantity isn't measured, and no trial has tested that jar.
That doesn't diminish fermented foods. It means the benefit they offer is a dietary one rather than a targeted therapeutic one — see probiotics vs prebiotics vs postbiotics.
Here fermented foods have something genuinely impressive, and it's worth knowing about.
A randomised trial at Stanford, published in Cell in 2021, put healthy adults on either a high fermented food diet or a high fibre diet for ten weeks, then measured microbiome composition and immune markers.
The fermented food group showed an increase in gut microbial diversity and a decrease in markers of inflammation. The high fibre group — despite fibre being the conventional recommendation for gut health — did not show the same increase in diversity over that period.
Note also what the trial required: participants ate several servings of fermented food daily — considerably more than the occasional spoonful of sauerkraut most people manage.
Three things, and they're the reasons to buy one:
What supplements don't provide is everything else food brings — fibre, protein, vitamins, polyphenols, and the fermentation by-products formed during the process.
| Feature | Fermented foods | Supplements |
|---|---|---|
| Guaranteed to be alive | No — many aren't | Yes |
| Named strains | No | Usually yes |
| Known dose | No | Yes |
| Microbial diversity | High | Low |
| Trial showing raised diversity | Yes | Rarely demonstrated |
| Nutritional value | Yes — it's food | None |
| Watch out for | Salt, sugar, histamine, alcohol | Cost, vague labelling |
Pure Encapsulations ProFloraGG 25B — £20.47 · 138 reviews · Available from Welzo. Three ingredients: the named GG strain at 25 billion CFU, a hypoallergenic carrier and a plant-derived capsule. This is the clearest illustration of what a supplement offers over food — you know the organism, the amount, and can look up the research. Dairy-free and shelf stable; stock is intermittent.
Swanson L. plantarum — £5.93 · 132 reviews · Available from Welzo. Around 20p a day. Fittingly, L. plantarum is one of the dominant organisms in sauerkraut and kimchi fermentation — so this is close to isolating a species you'd get from those foods, at a known dose. It names the species rather than the strain, so no specific trial evidence attaches.
Bloating and wind when increasing fermented foods are common and usually settle. Introduce them gradually rather than overhauling your diet in a week.
Take particular care with fermented foods if you
Home fermenting: follow a tested method. Improper technique — particularly with low-acid foods in sealed containers — carries a botulism risk. Discard anything that smells wrong, looks discoloured or has mould. More in probiotics safety.
On labelling: probiotics carry no authorised health claim in GB or the EU. Supplements are sold as food supplements and cannot legally be marketed as treating any condition.
See your GP — or seek urgent care — if you have:
Neither food nor supplement is a substitute for assessment. See when to see a GP and bowel cancer screening.
They're better as an everyday habit — there's trial evidence that eating more of them raises microbial diversity, which few supplements have shown. They're worse as a targeted tool, because you don't know which organisms you're getting or how many.
Live yoghurt, kefir, chilled raw sauerkraut and kimchi, unpasteurised kombucha, miso added after cooking, and some aged cheeses. Bread, beer, wine, coffee, chocolate, soy sauce, tempeh and shelf-stable sauerkraut do not.
Usually not. Most supermarket pickles are preserved in vinegar, which involves no live culture at all. Genuinely fermented pickles are salt-brined and sold chilled.
No. The fermentation happens before baking, and baking kills the organisms. Sourdough has other merits — flavour, and often easier digestibility — but live cultures aren't among them.
The Stanford trial used several servings daily, which is more than most people manage. Building towards one or two servings a day is a realistic target — increase gradually.
Yes. Heat kills live cultures, which is why miso should be stirred into soup off the boil and why cooked kimchi loses its live content — though it keeps its other nutritional value.
For general gut health, reasonably. For a specific purpose needing a particular strain at a particular dose — antibiotic cover, for instance — no. Food can't deliver that precision.
Pasteurised versions generally are, but avoid unpasteurised dairy, and be cautious with kombucha because it contains alcohol. Check with your midwife.
Often the fermentable carbohydrate rather than the bacteria, particularly if you have IBS. Histamine is another common culprit. Introduce them slowly, and stop if symptoms worsen rather than persisting.
If unpasteurised, it contains live cultures — but check the sugar content, as some brands are high, and note it contains small amounts of alcohol.
Medical disclaimer: This article is for general information and education only and does not constitute medical advice, diagnosis or treatment. Food supplements are not a substitute for a varied and balanced diet, and are not intended to diagnose, treat, cure or prevent any disease. Probiotic effects are strain-specific; because fermented foods do not declare named strains or CFU counts, published trial results do not transfer to them. Trial findings are described qualitatively; no figures are quoted because they could not be verified against source publications at the time of writing. Fermented vegetables such as sauerkraut and kimchi are high in salt, which matters if you have high blood pressure or heart failure. Fermented foods are high in histamine and tyramine — the latter is a significant interaction for anyone taking MAOI antidepressants. Live cultures should be discussed with a doctor if you are immunocompromised. Unpasteurised dairy should be avoided in pregnancy. Home fermentation carries a botulism risk if done improperly; follow a tested method. Prices and availability are correct at the time of writing.
About the author
Dr Zeeshan Afzal (MBBS) is a practising medical doctor and Welzo's Medical Content Lead. He writes and reviews Welzo's health content to ensure it is accurate, evidence-based and aligned with current UK clinical guidance.
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