Kimchi, kefir, kombucha, ’kraut. Mention the words “gut health” to anyone these days and the “four Ks” will spring to mind. Yet there are other ways to support your gut microbiome, many of which are cheaper and more readily available.

Sometimes they are better for you, too. “Many of those flavoured kombuchas and kefirs you find in the shops – they might have something notionally good, like fibre and culture, but these ingredients are often there simply to allow health claims to be put on products which are high in sugar and engineered to drive excess consumption,” says Chris van Tulleken, doctor and author of Ultra-Processed People: Why Do We All Eat Stuff That Isn’t Food … and Why Can’t We Stop? “You can’t have food that’s good and bad.”

He lists the ingredients on the back of a popular kombucha drink. “Black tea leaves, green tea leaves, then flavourings and sweeteners! We have a growing body of evidence that non-nutritive sweeteners negatively affect your health, even if in some ways they may be marginally better than sugar.” Real food – by Van Tulleken’s definition, unprocessed or minimally processed food – is complex, and there is little merit in pointing at one specific element of it and saying, “That’s good.”

“That includes taking fibre, antioxidants or cultures of good bacteria and adding them to a product that is otherwise ultra-processed. The science of what is good for our microbiome is still emerging, but there are some simple things we’re sure about. Whole or minimally processed fruit and veg, including beans and pulses, are good for you. Meanwhile, there is good reason to think that food with emulsifiers, gums, modified starches and non-nutritive sweeteners is probably not great for the bugs inside you.”

There is, says Tim Spector, co-founder of Zoe, the personalised nutrition company, and author of Food for Life, a growing body of evidence that eating fermented foods may support gut health, because they contain probiotics: live bacteria and yeasts that are thought to have health benefits. These include foods such as kefir – but they also include “commercially available fermented foods, such as some cheeses and full fat live yoghurt” as well as misos, vinegar and olives, which are unpasteurised.

Yet the cheapest, most readily available gut support of all comes in the form of prebiotics: substances in food that can’t be digested, but which feed the microbes that our gut already harbours. All fruit, vegetables and pulses contain prebiotics (some more than others) and “you don’t have to buy the most expensive products to get the health benefits. For instance, frozen and fresh vegetables have the same nutrients. Tinned beans and pulses are excellent value and easy to store,” says Spector.

The following is not an exhaustive list – but these are pro and prebiotic foods that, in their least processed form, will enrich your gut without worrying your wallet.

Probiotics

Cheese

It’s easy to forget that cheese is a fermented food because it’s often demonised. “It’s high in salt and fat,” says Van Tulleken. But it is also a rich source of bacterial cultures – even richer than fermented vegetables, says Bronwen Percival, cheese buyer for Neal’s Yard Dairy and co-founder of the fermented foods research site Microbialfoods.org. “In kimchi, you’ll get an extreme dominance of lactic acid bacteria, but in cheese you get an incredible diversity.” There are lactic acid bacteria, but there are also bacterial cultures associated with cheese maturing and ripening, and studies suggest “that really has an impact on the microbial diversity of the gut.”

This is particularly true of raw milk cheese – which is to say, cheeses made with unpasteurised milk (best avoided if pregnant or immunosuppressed), because heating the milk “will selectively kill a variety of those microorganisms”. Likewise, cooking a cheese, even if it’s unpasteurised, will compromise the number and diversity of microorganisms that make it into your gut. Neal’s Yard Dairy specialises in artisanal raw milk cheeses – and they’re not cheap – but Percival says you “don’t have to differentiate between a parmesan at Tesco and NYD’s Appleby cheddar. The Tesco parmesan is still going to be made with a whey starter [that is, the bacterial cultures that kickstart the cheese-making process].” The important distinction to draw is unpasteurised v pasteurised – although, she says, even pasteurised cheeses will have probiotic bacteria from the process of ripening.

Miso

Every morning, Jonathan Hope drinks miso – a salty, umami-rich paste made from fermented soya beans – with lukewarm water. He makes his own unpasteurised version which is full of koji mould. “It’s an easy way of incorporating live food into the morning of your day,” says Hope, who sells his miso via the online farmer’s market Wylde. “Like other fermented foods, miso naturally contains probiotics and is likely to support your gut microbiome,” says Spector.

“Although there haven’t been many studies on miso specifically, it may have potential health benefits if eaten as part of a balanced diet.” It’s richer in probiotic bacteria if it’s unpasteurised, as they’re killed off in the heating process (hence Hope’s lukewarm water), but “pasteurised miso is not bad for you, in the same way that pasteurised kimchi is not bad for you,” he says. Fermented grains and pulses are “still full of prebiotic fibres that the stomach will benefit from”. Miso is easy to incorporate into your diet and a little goes a long way, so even if the upfront cost is steep, it’s cheap long-term. Use it wherever you’d use salt, says Hope, and mix white and red to get a more balanced flavour profile.

Olives

There’s more to the health benefits of olives than monounsaturated fatty acids, says Federica Amati, head nutritionist at Zoe and author of Every Body Should Know This. As well as these “good-quality fats”, olives are rich in polyphenols that help gut bacteria thrive. This is true of “all olives, whether tinned, jarred or fresh” – but the advantage of seeking out unpasteurised olives is that they are a “live” food, like kimchi, and so rich in probiotic bacteria. “Olives are not edible straight from the tree,” explains Marianna Kolokotroni of Oliveology, who sells unpasteurised olives from Greece. “They need to be cured” – steeped in fresh water or brine solution for nine months – then preserved in olive oil and vinegar. Industrial-scale producers cure with caustic soda, which is quicker – but most producers pasteurise or sterilise their olives, whatever their process of curing. “Jarred, tinned, and any olives which are stuffed or pitted will be pasteurised,” she explains. They’re still healthy, but they’re not probiotic. Look for olives with stones from small-scale suppliers, and ask about processing. Also look out for Throuba olives, the only olives that can be eaten straight from the tree thanks to a fungus that enables them to lose their bitterness as they ripen.

Vinegar (not just apple cider)

Apple cider vinegar gets a lot of good press, but all vinegars are fermented, meaning they’re live if unpasteurised. “They are easy and cheap to make at home,” says Wylde Market’s founder Nick Jefferson, who sells artisanal vinegars made from seasonal ingredients, but also makes his own from leftover wine with equal amounts of water. “The ‘mother’ – the combination of cellulose and acetic acid bacteria, which develops on fermenting alcoholic liquids, and turns alcohol into gut-friendly acetic acid – does the rest.” It is this blend of bacteria and yeasts that can support the gut, and which you will probably see in vinegar that hasn’t been pasteurised. “Those stringy bits might look off-putting,” says Sarah Du-Feu, who makes vinegar with everything from elderflower to rhubarb, “but it’s a healthy sign.”

Prebiotics

Mushrooms

It’s easy to splash out on weird and wonderful mushroom varieties, but, while price may indicate taste, “it’s not a marker of health benefits. It’s good to try different varieties as you’ll get a diverse range of plant compounds,” says Spector, but “they’re all good. Even the humble button mushroom will support your health.” Their high fibre content “feeds your gut microbiome. They also contain a range of bioactive compounds that are not found in other foods and may benefit health, including [anti-oxidant] ergothioneine, which has several different roles in the body,” in defence and repair, says Amati.

Pulses

“There’s no such thing as a bad pulse,” says Amati – as long as they’re canned or dried, rather than ultra-processed. The growing popularity of pulses in recent years has seen companies produce pulse-based snack foods that have none of the benefits of beans in their minimally processed form. “You’re no better off with these than you are with a packet of crisps,” Van Tulleken says, reading the ingredients listed on a packet of lentil chips. “There’s 40% lentil flour, potato starch and a very long list of flavourings, all of which are in there to make you eat lots more than the ‘recommended’ 18g serving.” These snacks are not good for the gut – and they’re not cheap, unlike a can of beans or a packet of lentils, which will set you back no more than a few quid depending on quantity and where you buy them from. Posh jarred beans are divine, but there are no health benefits to buying fancier beans beyond flavour and texture. “Pulses are an excellent source of fibre and other healthy plant compounds, like polyphenols [which help our gut microbes],” Amati says, and that’s as true of an 80p can as it is of a £5 jar.

Dark chocolate

This is not carte blanche to feast on Bourneville. “Higher-quality dark chocolate with a cocoa content of 70% or more is best,” says Spector. The cocoa contains gut-friendly polyphenols, and the lower sugar content means it’s “difficult to consume lots in one sitting, and it can be more satisfying, due to its rich, bitter taste”.

Sourdough bread

Sourdough is sometimes described as a live food, but it’s not: the probiotics in the sourdough starter are killed when the bread is baked. The value of sourdough to your gut chiefly derives from the fibre it contains – but the bioavailability of that fibre depends on how it’s been processed. “Something for people to watch out for is ‘sourfaux’, which is what we call a product that’s marketed as sourdough but made by a shorter process involving baker’s yeast or other raising agents,” says Chris Young, coordinator of the Real Bread Campaign. “The necessary changes in the dough cannot occur to the same extent – or perhaps at all – if the all-important lactic acid bacterial fermentation is reduced or left out.” Worse still, many of these sourfaux contain emulsifiers, which are proven to be detrimental to the gut lining. Opt for sourdough that has been fermented slowly – preferably overnight – and made with stone-milled whole grains. “Good sourdough bread is healthy for most people. Bad sourdough bread is probably as unhealthy as other bread,” says Spector.

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