Kombucha, kimchi or kefir – which is the best for your gut health?

Whether you buy your lunch from the most esoteric of health food stores, or simply nip to the supermarket for a meal deal, you will have seen shelves bursting with “gut-healthy” kefirs and colourful kombuchas. Or perhaps you’ve found your eyes watering over the pungent punch of homemade kimchi.

What all of these have in common (aside from a first letter) is that they’re fermented foods, filled with microbes which are thought to boost gut health. Given good gut health has been linked to everything from better digestion to brain health, reduced risk of cancer, and protection from dementia, it’s easy to see why these drinks and dishes are having their moment in the sun.

With high-end bottles of kombucha at £45 a bottle are these healthy boosters really worth splashing out on?

“They all have a benefit in improving the diversity of good bacteria in the gut,” explains Dr Vijay Murthy, a functional medicine doctor to the British royal family at Murthy Health. “If you improve the diversity of good bacteria in your gut, you make it easier to digest food which can reduce certain digestive discomforts, such as bloating, constipation, diarrhoea or indigestion.

If you have a good gut microbiome, the good bacteria occupy spaces in the gut and flush out, deactivate, or even kill the bad gut bacteria which leads to improved immunity.

“Good gut bacteria also improve your ability to produce short-chain fatty acids,” Dr Murthy continues. “When the gut bacteria chew on fibre in the gut, they produce these acids, which are necessary for brain function, focus, reducing anxiety, nutrient absorption, and they’re also very important for good cardiovascular health.”

Here we break down the health benefits of each.

Kefir

Made from fermented milk, kefir is a drink with a yogurt-like consistency but has a tangy taste. Traditionally it would have been made in goatskin bags, but nowadays it’s available by the bottle in most supermarkets and health food shops.

“If we go by the available evidence and the number of studies that have been done, there are far more publications about kefir than kombucha or kimchi, so I’d say from a public health perspective, this is the most likely to be good for you,” says Dr Murthy.

Despite being made from milk, one interesting theory about kefir is that it may be beneficial for people who suffer from lactose intolerance. This is because the bacteria in the kefir “pre-digest” lactose in milk and may help encourage those bacteria to grow in the gut too.

“Kefir may also help alleviate other digestive issues like diarrhoea and constipation,” adds Emer Delaney, a dietitian and spokeswoman for the British Dietetic Association. “It has demonstrated anti-inflammatory properties in some studies, which could have implications for various health conditions. It may even support bone health too.”

Given it is similar to yogurt, many people drink kefir in the morning as part of breakfast, which might not be the worst strategy, thinks Delaney. “Many people find it provides an energy boost and supports digestion throughout the day,” she says.

When buying a kefir, it’s generally better to choose an unflavoured one, which generally contains fewer sweeteners and are often made with a wider range of bacteria, offering bigger gut health benefits.

Kimchi

Consumed in Korea for thousands of years, kimchi is a common side dish with a meal in Southeast Asian countries, made by fermenting cabbage or radishes with garlic, onion, and red chilli added. Though it can be somewhat pungent to create at home, the theory is that it has the same gut-boosting benefits as kefir.

“Studies have shown that kimchi can help improve digestion and reduce symptoms of digestive issues like bloating and constipation,” explains Delaney. “This is likely due to its probiotic content and the fibre from the vegetables. Kimchi has been found to have immune-boosting properties, potentially because of its probiotics and various bioactive compounds. Some studies suggest that kimchi may have anti-inflammatory effects, which could be beneficial for overall health and reducing the risk of chronic diseases.”

The fibre content of the vegetables in kimchi, and the fact it is often consumed with a main meal – often featuring even more fibrous vegetables – may be the key to its success.

“With all of these probiotic foods, you must consume them with plenty of fibre,” says Dr Murthy. “These bacteria live on fibre. If you consume them alongside the fibre, you give them something to chew on which helps them produce those helpful short-chain fatty acids. In the absence of fibre, probiotics can disturb the gut microbial population.

“The other thing is that kefir, kimchi, and kombucha are all acidic in nature,” adds Dr Murthy. “If you’re having them with other foods, that will encourage the gut to produce mucin which acts as a protective layer in the gut to prevent inflammation and indigestion from the acid.”

However, of the three, kimchi has the highest salt content and that can cause its own problems, especially in those who tend to or family history of high cholesterol.

“Several large studies raise the possibility that Koreans who eat lots of kimchi are at higher risk of stomach cancer, possibly related to the nitrates and salt content found therein,” says Dr Claire Merrifield, a GP and co-founder of home health testing company, Selph. “Further studies have suggested that it depends on the type of kimchi eaten, with cabbage-based kimchi healthier than radish-based.”

A supermarket variety of kimchi can include as much as 4g of salt per 100g, so a single spoonful could be as much as a third of a person’s recommended daily guideline amount of salt.

It might be better to consider making kimchi at home, suggests Delaney. “It’s useful as you can choose high-quality, organic ingredients and avoid any additives or preservatives; you can adjust the flavours and spice levels to your liking,” she says. “Homemade versions are typically fresher and may contain a wider variety of live and active cultures depending on your recipe; making your own can be more affordable in the long run, especially if you have these foods regularly.”

Kombucha

Traditionally made in China, kombucha is a drink made by fermenting tea leaves. In recent years it has become a popular alternative to alcohol for non-drinkers, with extensive claims made about its ‘gut-boosting’ effects.

While the drink purports to have the same effects on improving the gut microbiome as kefir and kimchi, those effects are unproven.

“Social media and marketing has done a great job of convincing us of their health benefits. There have been some studies in mice showing beneficial effects of kombucha on blood sugar,” says Dr Merrifield. “However there’s no convincing data in humans that kombucha is beneficial for gut health or the gut microbiome.”

One potential positive about kombucha is that it is thought to contain anti-oxidants which help prevent cell damage to reduce inflammation and could contribute to anti-ageing effects.

However, before you go out to swap all your drinks for kombucha, remember that most contain caffeine, usually less than coffee and tea, although it varies by brand, and some are sweetened with significant amounts of sweeteners and flavourings to counteract the bitter taste.

The verdict – which is the healthiest: kefir, kombucha or kimchi?

Of the available research, most points towards kefir as being the “best” for your gut.

However, it’s important to remember that fermented foods may not work for everyone. “If your digestive system is already suffering from a bacterial imbalance – what we call small intestinal overgrowth – then adding more bacteria via fermented food may worsen symptoms,” says Dr Murthy. “Much like dairy or gluten, the benefit is dependent on whether the person can tolerate it or not.

“Kefir, kimchi, and kombucha all contain high levels of histamine, a chemical which is usually produced in the body to help it respond to allergens,” Dr Murthy continues. “If one has histaminic overactivity then they could get skin hives, rashes, brain fog, and even disturbed sleep, so be careful.”

What’s the best way to eat fermented foods?

The best approach to starting consuming fermented foods is to go slowly. Have one tablespoon (preferably with a fibre-filled meal) and examine the effect on you. Expect an initial “adjustment period” where you may feel some bloating or digestive discomfort. “Usually your body will adapt within around 72 hours, so if you feel alright by then, have another tablespoon and you can work up from there,” says Dr Murthy.

A tablespoon of any fermented food every two or three days should be sufficient for the average adult, says Delaney. Bear in mind it is possible to consume too much-fermented food (though exactly what constitutes ‘too much’ can vary between people so it’s best to start with small amounts and work your way up) “which can cause digestive upset like bloating, gas, nausea, and diarrhoea,” she adds. “This is due to the increase in probiotics and the potential for them to interact with your existing gut bacteria.”

The final thing to remember is that while these foods are very fashionable (and often expensive as a result) you might get the same benefits by eating a little more simply.

“There’s far better evidence that yogurt and hard cheeses are beneficial for your gut health,” says Dr Merrifield, “so if you want to have fermented foods and don’t like kimchi, kombucha or kefir, they’re a reasonable alternative.”