Wellness Tips

Do fermented foods live up to the hype? Expert tips on how to boost your microbiome

From kimchi to kefir to kombucha, the popularity of fermented foods is soaring. Dietitian Orla Walsh explores the potential benefits, and the latest research

Fermentation is a natural process involving microorganisms like yeast and bacteria, which convert sugars into new products through chemical breakdown. Put simply, the bacteria pre-digest the food or drink. Most people are familiar with the work of yeast, making alcohol and delicious bread. While the fermentation of already healthy foods adds a unique taste to food and beverages, it also changes its nutritional benefits and properties.

Fermented foods can be nutritional powerhouses, loaded with beneficial bacteria, and potentially supporting gut health. For example, research has shown that people who eat fermented plants at least once a week have slightly different gut bacteria than those who don’t. Fermentation can also enhance the nutrients within the food and remove antinutrients.


Kefir is a fermented milk drink. As well as making your own, it is widely available in most supermarkets. It’s produced by adding kefir grains to milk. Dairy-free water kefir is also an option, and thrives on sugar as well as fruit sugar.

Kefir has a sour, tangy taste and feels slightly fizzy due to the carbon dioxide produced by the fermentation process. If made with dairy, it’s not only a rich source of calcium but also a good supplier of probiotic bacteria. It has a higher probiotic count than conventional yoghurt, making it an attractive option for those interested in gut health. Research also suggests it may help with blood sugar control.


Kombucha is a fermented drink. It’s usually produced by fermenting sweetened tea, often black or green, through the addition of a scoby — a symbiotic culture of bacteria and yeast. Although other fizzy drinks are made from carbonated water, artificial flavours and sugar or sweeteners, kombucha gets its bubbles from the fermentation process. The sugar content of these drinks does vary, so read the label.


Kimchi is a staple of Korean cuisine. It’s made from fermented veggies like cabbage and radish, and is often flavoured with healthy spices, adding an even stronger taste. It’s a definite flavour bomb that can bring a boring sandwich or salad to life. It also provides extra vitamins and probiotic bacteria.


It would be wrong to forget about the more commonly eaten fermented food, yoghurt. Yoghurt is made by adding bacteria to milk. Sometimes yoghurts have extra bacteria added, so look out for ‘live cultures’ on the label.

​What are the known health benefits of fermented foods?

What can shock people is that with some fermented foods, the microbes are not alive when they are consumed — they may have been killed off in the cooking and manufacturing process, as occurs with sourdough bread, tempeh and some long-life kimchi and fermented products. So not all fermented foods provide probiotic bacteria. However, some provide live bacteria, such as fresh kimchi, kefir, kombucha and some cheese. This is important to know, if choosing to eat a certain fermented food because you want to eat more ‘good bacteria’.

Fermentation also enhances the nutritional value or digestibility of the food. For example, increasing vitamin B12 and folate concentrations. It has also been shown to reduce gluten in foods. This doesn’t mean items are gluten-free or suitable for those with coeliac disease, though it can help some people better tolerate bread. Live yoghurt cultures can improve the digestion of lactose in yoghurt, which helps those with lactose intolerance to enjoy their yoghurt without the same gut issues.

Despite all of this and the benefits described, is there a heap of evidence advocating for the regular use of fermented foods and drinks for health benefits? No, there is not. This doesn’t mean you shouldn’t include them for potential benefits, and they certainly should be enjoyed for their delicious taste. However, there’s more talk about them than research into them — except fermented dairy.

The parts of fermented dairy that provide the body with benefits include the likes of vitamins, conjugated linoleic acid, short-chain fatty acids and bioactive peptides. Additionally, the fermentation of lactose results in the formation of prebiotics which stimulate beneficial bacteria in the colon. Nonetheless, a lot of the research is pointing at the health benefits of fermented dairy on immune responses such as inflammation and its defence against pathogens. Furthermore, there also appear to be benefits in terms of heart health, bone health, digestion and weight management.

Despite their numerous benefits, fermented foods might not be everyone’s cup of tea. They often contain high levels of histamines, which could worsen symptoms in individuals with histamine intolerance.

The growth of fermented foods in our modern diet serves as a testament to their historical relevance, unique taste profiles, and health-enhancing properties. And as our comprehension of the intricate connection between our gut and our overall well-being deepens, the role of gut-friendly foods such as these becomes more prominent.

In light of the growing awareness about the benefits of a healthy gut and varied microbiota, fermented foods like kefir, kombucha, and others are unlikely to be merely a passing fad. Instead, they mark a return to traditional dietary practices that prioritise natural and wholesome foods.

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