What’s the deal on fermented foods – do they really help with gut health?

gut health thrive magazine

Fermentation of foods and beverages have been known and used by humans for millennia for food preservation, safety and flavour enhancing properties.  Many types of food groups, including dairy, vegetables, starchy roots, legumes, and fruits, as well as meat and fish, can be fermented.

Fermented foods hold a special place almost in every culture and some of the most popular fermented products originated from around the world:

  • kefir (fermented milk) from Caucasus,
  • kombucha (fermented tea) from China,
  • natto and miso (fermented soybean and soybean paste) from Japan,
  • kimchi (fermented vegetables) from Korea,
  • sourdough bread from Middle East and Europe,
  • tempeh (fermented soybeans) from Indonesia.

Recently, fermented foods have seen a surge in popularity, driven by claims of their health benefits, as well as increasing interest in healthy lifestyle and gut health, in particular. But do the fermented products really have health promoting effects and deserve all the accolades?

The most widely researched fermented food is kefir , followed by sauerkraut, natto and sourdough bread.  While kombucha, miso, kimchi and tempeh are extensively studied in vitro, there are no randomised controlled trials (“RCT”) studying their benefits for gut health in humans. It certainly does not mean we should not consume these particular foods!

Health benefits of fermented foods

  • Probiotic effect of fermented foods

Unlike food processing, fermentation process retains the enzymes, vitamins, and minerals in foods and beverages. The biggest benefit, however, comes from the probiotics they may contain.  While it is hard to quantify a microbial content in fermented products (it depends on a type, region of production and age), most fermented products contain at least 106 microbial cells per gram.

Whether the microorganisms can actually reach the gut largely depends on a product. Their presence in the gut has also a transient effect. Nonetheless, these organisms still have a beneficial effect, as they compete with pathogenic bacteria and produce a host of beneficial immune-regulatory by-products.

Kefir grains, for example, contain a large variety of beneficial bacteria (e.g. Lactobacillus kefiranofaciens, Bifidobacterium) and yeasts (e.g. Candida kefir) which have been shown to correct dysbiosis by adhering to gastrointestinal mucus, protect against the invasion of pathogens and their toxic effect.

There is some evidence from RCTs demonstrating that kefir may be beneficial for H. pylori eradication and lactose malabsorption. Kefir consumption was also found to increase beneficial bacterial load and reduce inflammation markers in patients with inflammatory bowel disease.

  • Fermentation produces new beneficial compounds

Not only fermented foods may be a source of live organisms with probiotic qualities, fermentation process could introduce completely new compounds to the food. For example, lactic acid bacteria both from dairy and non-dairy foods generates bioactive peptides and polyamines which have a potential beneficial effect on cardiovascular, immune and metabolic health.

Another example is an enzyme nattokinase produced during fermentation of natto. Nattokinase is used in treatment of cardio-vascular diseases, high blood pressure and blood clots.

  • Health benefits from prebiotics and vitamins in fermented foods

Besides containing probiotics, the process of fermentation also produces prebiotics, which in turn feed probiotics.  Additionally, microbial flora used in fermentation can influence vitamin composition. Propionibacterium peterssoni and Propionibacterium pituitosum found in kefir produce vitamin B12, whereas Freudenreichii subsp. Propionibacterium Shermanii support vitamin B6 production.

  • Fermentation reduces toxins and anti-nutrients

Fermentation of soybeans may reduce phytic acid and sourdough fermentation can reduce the content of fermentable carbohydrates making them easier to digest for someone with irritable bowel syndrome.


Are the fermented foods good for everyone?

While fermented foods may confer health benefits on some people, they are not suitable for everyone. Fermented foods are high in histamine, therefore, anyone with histamine sensitivity may find fermented foods contributing to their symptoms.  Additionally, people with small intestinal overgrowth (“SIBO”) may find consumption of some fermented foods challenging, as it could aggravate their symptoms.

These days there are so many different types of fermented products to choose from: pickles, sourdough, cheese, yogurt, kefir, sour cream, salami, vinegar, soy sauce, miso, natto, tempeh, kimchi, sauerkraut, kombucha, kvas and more.

If you are new to fermented foods, then starting slowly and with smaller portions would be recommended. Also it may worth starting with relatively mild flavours like yogurt, kefir and sourdough before trying the likes of kimchi and natto.

There is enough evidence to suggest that fermented foods provide benefits way beyond the “starting materials”.
Potential probiotic effect enriched nutritional profile as well as health conferring properties of different metabolites make fermented foods a dietary “must have” for anyone looking to optimise their gut health. Regular consumption of a variety of fermented foods in small portions may provide some health benefits. However, like with any other foods, they may certainly cause undesirable reaction in sensitive individuals, whether due to their high histamine load or probiotic effect.

As featured inside Thrive Magazine Summer 2021 >>

Elena holds a Nutritional Therapy Diploma (DipION) from the Institute for Optimum Nutrition and is working towards BSc (Hons) Nutritional Therapy degree from the ION.