From an ancient fermented yoghurt to a spiced Korean cabbage dish, experts say a handful of simple diet swaps could strengthen your immune system - and even reduce your risk of cancer.

While these foods have been around for thousands of years, products such as kefir, kimchi and kombucha have surged in popularity in recent months. 

And with a growing body of research pointing to their health benefits, doctors hope this is more than just another wellness fad.

Fermented foods are made when bacteria or yeast break down natural sugars. Some, such as yoghurts and kefir, contain probiotics - live strains of bacteria that support gut health.

They are now seen as a key way to boost the body's population of 'good' gut microbes, improving the microbiome - the vast community of micro-organisms in the digestive tract linked to better digestion, lower inflammation, stronger immunity and even improved mental wellbeing.

A growing number of studies back up the claims. 

A 2025 review in Frontiers in Nutrition found fermented foods can ease bloating and improve bowel regularity, while a 2022 analysis by Chinese researchers linked foods such as yoghurt and kimchi to better heart and metabolic health.

Some studies have even suggested fermented foods could influence mood via the gut–brain axis, potentially easing symptoms of depression and anxiety - although scientists stress research in this area is still emerging.

'There are a host of health benefits from eating fermented foods,' says Dr Sean Preston, Consultant Gastroenterologist at London Digestive Health. 

'The primary reason for this is the probiotic, or live bacteria, that is present, which can help digestion and support the gut microbiome.

'Theoretically there is also a possible benefit of reducing the risk of bowel cancer by creating a diverse gut microbiome and preventing the production of pro-carcinogenic compounds.'

It's no wonder, then, that fermented foods have become big business — the global market is now worth an estimated £67 billion and is expected to increase fivefold within the next decade.

But experts say the key to unlocking their full benefits is to make them yourself.

Shop-bought jars don't always deliver the same punch, as many pickles and fermented-style products are preserved using vinegar rather than natural fermentation with live organisms — meaning they lack probiotics.

To make sure you're getting the real thing, Dr Preston advises looking for labels that say 'naturally fermented', and checking for tiny bubbles in the liquid once opened — a sign that live bacteria are active. Also avoid products with added sugars or preservatives, which can interfere with the fermentation process.

With that in mind, here are five fermented foods packed with gut-boosting benefits — and how to make them yourself.

Kefir

Kefir is a type of cultured dairy product, rich in probiotics, vitamins and even has antibacterial properties. Research has suggested that fermented milk can boost digestion and help improve the body's immune response.

'Kefir has been everywhere recently and that is likely to do with the fact that it is more palatable than many other fermented foods,' says Dr Preston. 'However, that means that many of the supermarket versions are high in sugar and added flavourings, so the benefit will not be as great.

'A poor kefir is no better than a good natural yogurt for you, however a good quality kefir has a number of added benefits because of the additional lactobacillus bacteria.'

Research has also linked kefir to improved brain health.

A small trial involving people with Alzheimer’s disease found that drinking kefir daily for 90 days led to a 28 per cent improvement in overall cognition and a 66 per cent boost in immediate memory tests.

Laboratory studies suggest compounds in kefir may also reduce inflammation and oxidative stress in the brain, mechanisms thought to play a role in slowing cognitive decline.

It's made by adding kefir grains – a combination of yeast and bacteria – to milk. This results in a thick, tangy beverage that tastes similar to yogurt.

Although you can buy Kefir for around £3 a litre, kits where you add kefir cultures to milk and let it stand for 24 hours can produce over 100 litres for £15 (plus the milk needed for the recipe).

Kimchi

Korean staple kimchi is a fiery, tangy mix of fermented cabbage, garlic, ginger and chilli that's been made for centuries as a way to preserve vegetables through the winter.

During fermentation, friendly bacteria – mainly Lactobacillus – flourish, giving kimchi its signature sourness and a host of potential health perks.

Studies have shown these natural probiotics can help support gut health, reduce inflammation and may even play a role in heart and metabolic health.

A 2022 study by the World Institute of Kimchi, even found that a higher level of consumption of the fermented cabbage was linked to 15 per cent reduction in body mass index (BMI) and a 12 per cent decrease in being obese.

'Kimchi is great because it tastes great and is easy to incorporate into daily meals,' says Dr Preston.

'But also the antioxidants in kimchi can also help reduce inflammation. It is also often high in Vitamin C.'

Kombucha

Kombucha is a fizzy, tangy drink made by fermenting sweetened tea with a culture of bacteria and yeast.

This process creates a lightly effervescent beverage that contains probiotics, organic acids, and antioxidants.

Although it originated in China more than 2,000 years ago, kombucha has surged in popularity in recent years as part of the wellness and gut health movement.

One of the main reasons kombucha is linked to health benefits is its probiotic content.

The live bacteria produced during fermentation can help support the balance of microorganisms in the gut, which plays a key role in digestion, nutrient absorption, and immune function.

Some studies suggest that a healthy gut microbiome may also influence mood and energy levels, though more research is needed to confirm these effects in humans.

'Pure natural kombucha is great for you because of the probiotic content, however it can be really funky which is why the supermarket version is often high in sugar or flavourings, so you need to watch out for that if you go for a store bought version,' says Dr Preston.

To make kombucha, start by brewing a batch of sweetened black or green tea and letting it cool. 

Add a SCOBY – a symbiotic culture of bacteria and yeast – along with some starter tea from a previous batch, then cover the jar and leave it to ferment at room temperature for 7 to 10 days. 

Miso

Miso is a traditional Japanese seasoning made by fermenting soybeans with salt and a type of mold called koji.

Sometimes rice, barley, or other grains are added to create different varieties and flavours, ranging from pale and sweet to dark and intensely savoury.

The result is a thick paste used in soups, marinades, and sauces, celebrated for its distinctive umami taste and rich nutritional profile.

The fermentation process that creates miso also produces beneficial bacteria and enzymes, which can support gut health.

Like other fermented foods, miso contains probiotics that may help maintain a healthy balance of gut microbes – essential for digestion, nutrient absorption, and immune function.

Some studies have linked regular consumption of fermented soy products to improved digestive health and reduced inflammation.

Miso is also a source of plant–based protein, vitamins, minerals such as zinc, manganese, and copper, and antioxidants that can help protect cells from oxidative stress.

Because it's made from soybeans, miso contains isoflavones – naturally occurring compounds that may contribute to heart and bone health.

'While you are not going to be consuming mountains of miso, it is easy to incorporate into your weekly meals, and it provides a diverse set of bacteria to help the gut microbiome,' says Dr Preston.

To make miso at home, cook soybeans until soft, then mash them with koji (a fermented grain) and salt.

Pack the mixture tightly into a container, weigh it down, and leave it to ferment in a cool, dark place for several months to a year, depending on the desired flavor

Sauerkraut

A jar of sauerkraut might look simple, but this humble mix of cabbage and salt is one of the oldest fermented foods in Europe.

When cabbage ferments, it becomes naturally rich in beneficial bacteria such as Lactobacillus plantarum, along with vitamins C and K and plant compounds that act as antioxidants.

'Sauerkraut is a great source of fibre, plus an additional source of vitamins that you may not get from other fermented foods,' says Dr Preston.

'The key is eating fermented foods little and often and ensuring that you are eating a diverse mix of foods, to ensure maximum benefits.'

Sauerkraut is made by finely slicing fresh white or green cabbage, then mixing it with salt – usually about 2per cent of the cabbage's weight. 

The salted cabbage is packed tightly into a jar or crock, pressing it down until it releases enough liquid to submerge itself in brine.