When it comes to dietary advice, eating more fermented foods such as kefir, kimchi and kombucha can be a tough sell – cue images of gassy concoctions fizzing away in cloudy jars or strange foodstuffs slowly going mouldy at the back of the fridge.

Fermentation is an age-old preservation technique by which microorganisms like yeast and bacteria convert carbohydrates, namely starch and sugar, into alcohol or acid.

Fermentation produces microbes called probiotics (often referred to as ‘good bacteria’), which help increase the diversity of the bacteria in the gut microbiome so it can function optimally.

Studies have revealed many health benefits of probiotics, from improving digestion to enhancing immunity. One study, involving 274 adults with irritable bowel syndrome (IBS), found that consuming 125g of fermented yoghurt daily for six weeks improved their symptoms, including bloating and constipation.

Is fermented food the same as a probiotic?

In the sense that probiotics are a byproduct of the fermentation process then yes, but it’s important to note that not all fermented foods contain the live probiotics that confer health benefits. For example, beer and wine are fermented but they do not contain live bacteria by the time we come to drink them. Similarly, if fermented foods are subsequently heat-treated (pasteurised) then there will be no probiotic activity.

Studies have revealed many health benefits of probiotics, from improving digestion to enhancing immunity.

Furthermore, not all products claiming to support gut health are fermented or contain probiotics. Some gut shots you’ll find in the supermarket chiller cabinet are simply combinations of fruit juice with other ingredients that can aid digestion, such as turmeric and ginger. Check to make sure the product you are buying contains probiotics – you should see words such as “contains live cultures”, and lactobacillus or bifidobacterium listed in the ingredients.

How often should you have fermented foods for gut health?

According to the gut health guru Professor Tim Spector, the key is to include a small amount of fermented foods daily, rather than consuming a large amount once in a while. He has, for example, a shot (approximately 100ml) of kefir every morning, along with a glass of kombucha two to three times a week, and some kimchi with cheese twice a week. If you are just starting out with fermented foods, go slowly as there can be an initial and temporary increase in gas and bloating.

Who should not eat fermented food?

While fermented foods are safe, and indeed healthy, for the vast majority of the population, some groups may wish to avoid them. Being high in histamines and salt, people with histamine intolerance or those on a low-sodium diet, for high blood pressure say, should exercise caution. Unpasteurised foods containing live bacteria, such as unpasteurised cheeses, are also not recommended for those with compromised immune systems and pregnant women.

The top easy-to-buy fermented foods

Fermentation gives foods a tart, tangy and sometimes sour flavour which can be an acquired taste, but given their amazing health benefits it’s worth seeking out those you enjoy. There are plenty of options available at the supermarket these days. Here are some of the best – and thankfully one of them is cheese!

Yoghurt and kefir

Live yoghurts and kefir are two of the more user-friendly probiotic foods, excellent for breakfast paired with fresh fruit and chopped nuts. Whilst both are essentially fermented milk products, kefir is fermented for longer and generally contains more probiotics than yoghurt, but it is also runnier and has a “funkier” flavour profile. If you prefer the taste of yoghurt then opt for authentic Greek yoghurt which is strained and therefore has a higher concentration of protein and probiotics. There are also some kefir fermented yoghurts available now which offer the best of both worlds. Choose plain, natural yoghurts and kefirs with no added sugar.

Cheese

Probiotics are found in cheeses that have been aged, but pasteurised. The best cheeses to go for are cheddar, gouda, edam, gruyère and parmesan. As cheddar is the nation’s favourite cheese, this is a great probiotic staple. Choose an aged one for the best health benefits.

Kimchi

Kimchi is a traditional Korean dish made with salted, fermented cabbage and other vegetables, with a spicy hit of chilli. It is usually eaten as a condiment alongside other foods and it’s also a great pairing with cheese. Many of the brands you’ll find in the supermarket are pasteurised to enhance shelf-life, which means all those lovely live bacteria have been killed off, so choose a “raw” one from the chiller cabinet instead.

Sauerkraut

Sauerkraut has a poor reputation for being both pongy and prosaic, but this fermented cabbage dish, originally from central Europe, is having a resurgence thanks to the increasing popularity of fermented foods. As with kimchi, many varieties you see are pasteurised, but there are some with live cultures. Again, look for those stocked in the chiller section.

Miso

Miso is a delicious paste of fermented soybeans that can be used as the base for soup or as an umami-packed flavouring in marinades and dressings. Again, you need to watch out for pasteurised versions as any heat treatment will destroy the live bacteria. For the same reason it’s important not to heat your miso to a very high temperature, just add it to foods at the end of cooking and, when making miso soup, the water should not be above 70C.

Apple cider vinegar

Vinegar doesn’t immediately spring to mind when it comes to probiotic foods, and indeed most are not, but there is a type of raw, unfiltered apple cider vinegar which contains a cloudy substance called “the mother” which is full of enzymes and beneficial bacteria. Apple cider vinegar can be taken as a shot (dilute with water), but is perhaps more often used as the base for salad dressings. Make sure to give the vinegar a good shake before using as the mother tends to settle at the bottom of the bottle.

Kombucha

If you fancy getting your probiotics in liquid form look no further than kombucha, a delicious fermented tea with a slight vinegary tang. Sugar is added as part of the fermentation process but some residual sugar may remain. It’s worth checking the sugar content in the nutritional information as they do vary, remember that 4g of sugar is one teaspoon. Brands which market their kombucha as sugar-free usually have sugar substitutes added to sweeten the product which studies have shown can negatively affect the gut.

The Daily Telegraph (London)