Best Kefir and Fermented Foods UK (2026): What the research Says

What are fermented foods, and why the interest?

Fermented foods are made by letting bacteria or yeasts break down sugars in milk, vegetables or tea. Kefir, yoghurt, sauerkraut, kimchi, miso and kombucha are common examples. Some still contain live microbes when you eat them; others are heat-treated after fermentation, which kills the microbes but keeps the flavour.

Interest jumped after a 2021 Stanford study published in Cell. Researchers randomly assigned 36 healthy adults to a high-fibre diet or a high fermented food diet for 10 weeks. The fermented food group, building up to about six servings a day, steadily increased the diversity of their gut microbes and reduced 19 inflammatory proteins in the blood, including interleukin-6. The high-fibre group did not see the same diversity boost.

That is exciting, but it was a small, short trial in healthy Californians, several authors have commercial interests in microbiome companies, and it measured markers rather than health outcomes such as fewer illnesses.

Our picks at a glance

How we chose

We picked products sold chilled or labelled as containing live cultures, with short ingredient lists and little or no added sugar, from brands widely available in UK supermarkets or direct. We covered the main fermented food types so you can build variety, which is what the Stanford diet did. We checked live prices at Morrisons and brand sites.

What does the evidence show, food by food?

Kefir and yoghurt

Kefir is fermented milk with a wider range of bacteria and yeasts than most yoghurts. It is a good source of protein and calcium, and people who struggle with lactose often tolerate it better because fermentation breaks some lactose down. However, a 2025 meta-analysis of seven trials found no significant overall effect on blood pressure or CRP (an inflammation marker), though longer use (8 weeks or more) lowered CRP in a subgroup.

Sauerkraut and kimchi

These fermented vegetables add fibre as well as microbes. Chilled, unpasteurised versions are more likely to contain live bacteria. Shelf-stable jars and tins are usually pasteurised (heated), which kills them. Both are salty, so portions of a forkful or two are sensible.

Kombucha

Fermented sweet tea. A systematic review found only one human study of its health effects. Treat it as a lower-sugar alternative to fizzy drinks rather than a health product.

Probiotics vs fermented foods

The NHS notes that probiotics are classed as food rather than medicine, so labels are not checked for live counts or survival to the gut, and evidence is limited to specific uses such as some IBS symptoms. The same caution applies to fermented foods.

Our picks in detail

Biotiful Kefir Drink Original: best everyday kefir

The UK's best-selling kefir, made with pasteurised British milk fermented with live cultures, with no added sugar in the original. Mild enough for beginners. Caveat: made with set cultures rather than traditional kefir grains, and live counts at the end of shelf life are not published.

Yeo Valley Organic Kefir Natural: best organic

Organic whole milk fermented with 14 strains of live yoghurt and kefir cultures, tangier than Biotiful. Caveat: organic is about farming standards, not extra gut benefit.

Vadasz Garlic & Dill Sauerkraut: best chilled kraut

Naturally fermented, kept in the fridge, and made from cabbage, cucumber, salt and spices only. Caveat: salty, and live counts are not stated.

Loving Foods Organic Kimchi: best unpasteurised kimchi

Certified organic, sold unpasteurised and chilled, from a small UK producer. Caveat: pricier than supermarket kimchi and needs delivery.

How to fit fermented foods into your day

• Breakfast: a glass of plain kefir, or kefir poured over oats with fruit.
• Lunch: a forkful of sauerkraut in a sandwich, salad or jacket potato.
• Dinner: kimchi alongside rice, eggs or stir-fries; a spoon of miso stirred into soup at the end of cooking (boiling kills live cultures).
• Drinks: choose water or plain kefir rather than sweetened or flavoured fermented drinks.

Spread servings through the day and keep a jar of chilled kraut or kimchi in the fridge, where it keeps for weeks once opened.

Who should be careful?

• Weakened immune system or pregnancy: speak to your GP or midwife about unpasteurised foods. The NHS says probiotics appear fine for most people with a healthy immune system.
• Salt: sauerkraut and kimchi are salty. Keep portions small if you have high blood pressure.
• Histamine intolerance: fermented foods are high in histamine and can trigger symptoms.
• Added sugar: flavoured kefirs and yoghurts can contain several teaspoons per pot.
• Alcohol: kombucha naturally contains traces of alcohol from fermentation.

If you want to try it: what to look for

1. 'Live', 'raw' or 'unpasteurised' on the label, and sold in the chilled aisle.
2. Short ingredient lists with no added sugar for daily use.
3. Variety: the Stanford diet mixed yoghurt, kefir, kraut, kimchi and kombucha.
4. Start with one serving a day and build up to let your gut adjust.

Bottom line

Adding a few servings of fermented foods a day is cheap, tasty and backed by early but promising evidence. Plain kefir from Biotiful or Yeo Valley is the easiest start, with a forkful of chilled kraut or kimchi alongside meals. Do not expect kombucha to do much beyond replacing a sugary drink.

Flavoured kefir yoghurt and sweetened or flavoured kombucha are excluded under our UPF selection policy. Plain kefir remains our starting point.