Fermented food: is it healthy? The honest story.

Fermentation is one of the oldest techniques we know for making food tastier, longer lasting and easier to digest. But in recent years, you hear more and more often that fermented food is also healthy. Is that true? And what exactly is fermentation? In this article, we explain what fermentation is and give you an honest, nuanced picture of what science currently has to say about it.

Fermented food is food that has been transformed by micro-organisms: bacteria, yeasts or moulds. These micro-organisms convert sugars and other compounds into substances like lactic acid, alcohol or acetic acid. That may not sound very appetising, but you eat the results almost every day: yoghurt, cheese, beer, wine and sauerkraut are all fermented products.

Fermentation is not new. For thousands of years, long before the invention of the fridge, people have used it to preserve food. But it does more than that: it also changes the flavour, the texture and the digestibility of what you eat.

A short, workable definition: fermentation is the transformation of food by micro-organisms to make it tastier, longer lasting or easier to digest.

Is fermented food healthy? The short answer: yes, fermented food can contribute to your health. But the honest answer is more nuanced than most websites will tell you.

What we know for certain

Let’s start with what is well supported. Eating fermented food demonstrably improves digestion. Recent large-scale meta-analyses (from 2025 and 2026) show that people who regularly eat fermented food have better bowel movements, less bloating and less gas. That’s not spectacular news, but it is solid evidence.

Fermentation also provides reliable help for people with lactose intolerance. The lactic acid bacteria in yoghurt and kefir break down a large portion of the lactose in milk. Many people who cannot tolerate regular milk can eat yoghurt or kefir without any problems.

What is likely

There are modest indications that fermented dairy, particularly yoghurt, is associated with a lower risk of type 2 diabetes and cardiovascular disease. These findings come mainly from large population studies. That is encouraging, but it is not hard proof yet. People who eat a lot of yoghurt often live healthier lives in other ways too, which makes it difficult to determine whether the yoghurt itself makes the difference.

What we don’t know yet

Then there are the claims you frequently come across online: fermented food is said to strengthen your immune system, protect your brain and even prevent cancer. The reality is that the scientific evidence for these claims is still very thin. Much of it is based on animal experiments or laboratory studies, not on research in humans. The European Food Safety Authority (EFSA) consistently refuses to approve health claims based on this type of evidence.

One more thing worth knowing: not all fermented products still contain live bacteria by the time you eat them. Supermarket kombucha is almost always pasteurised (heated), which kills the bacteria. If you want live bacteria, choose unpasteurised products, or make them yourself.

Fermenting at home is simpler than you think, and you don’t need expensive equipment. It’s great fun and you can let your creativity run wild. Start with something easy: a batch of yoghurt with a starter culture (ready in just 6 hours), sauerkraut that needs nothing more than cabbage and salt, or a glass of water kefir.

Research shows that the health effects are considerably stronger for artisanally produced fermented foods than for their industrial counterparts, for instance in the case of milk kefir. One more reason to have a go yourself.

Our Introduction to Fermentation course teaches you everything about the technique, so you understand what you’re doing. Because that’s the trick: once you understand how fermentation works, you can ferment anything.