Defined by the World Health Organisation as “Live microorganisms that when administered in adequate amounts, confer a health benefit on the host”. Probiotic bacteria can be added to food products like yoghurt or taken as food supplements, and are often described as “good” or “friendly” bacteria. Probiotics are meant to help correct dysbiosis- a condition where the natural balance of bacteria in your gut is disrupted by an illness or antibiotic or other treatments.

Probiotic bacteria break down fibre and resistant starches in our large bowel, which creates some incredibly useful by-products- short-chain fatty acids (SCFAs). They act as energy fuel for the bowel lining and therefore keep it healthy. They also have a positive impact on inflammatory processes and are protective against cancer cell formation. SCFAs have a huge role in maintaining the integrity of the intestinal barrier which ensures that the nutrients, water and ions are allowed through to the blood, but any pathogens and bacterial toxins are kept within the bowel for excretion with the faeces. Other products of fermentation include gases (hydrogen, carbon dioxide, and sometimes methane), which can make you feel bloated and cause flatulence- a completely natural part of healthy digestion!

In addition to the benefits to the bowel health, gut microorganisms play a pivotal role in the regulation of metabolic, endocrine and immune functions, although the mechanisms via which this is achieved are not yet fully understood.

Probiotics are described first by genus, then species and then by strain (i.e. Bifidobacterium infantis 35624). There are significant differences in their functions even at the strain level; therefore, for example, only because this specific strain (Bifidobacterium infantis 35624) was shown to benefit people with IBS (human trials), it does not mean that all other Bifidobacterium strains will have the same effect! For this reason it is difficult to interpret meta-analysis that combine studies using different probiotic products, because you are not comparing like for like. The best option we have at the moment is look at studies on specific probiotics and whether they show any evidence of positive benefits (providing the studies are of high quality!).

Live microorganisms are found in fermented products such as kefir, kombucha, kimchi and sauerkraut. They cannot be called probiotic products in the EU and UK, because they do not fit the World Health Organisation definition of a probiotic product (see the beginning of this post). We do not know what bacteria strains or how much bacteria a fermented product that you produce at home or buy in a shop contain, therefore, we cannot know exactly what benefits it may bring. Although there is some evidence to suggest that fermented products may offer benefits similar to probiotic supplements, they cannot be prescribed as a treatment for a condition or a disease.

Fermented foods can be a delicious addition to everyone’s diet. The fermentation process can make certain foods more easy to tolerate (i.e. sourdough bread and fermented diary= kefir and yoghurt), so they may be preferable if you tend to have difficulties with the unfermented counterparts (i.e. regular yeast bread or regular milk). In addition to improved digestibility and the potential benefit of live microorganisms within, fermented foods contain more vitamins (esp. B12 and folate). If you don’t usually have fermented foods in your diet and want to change this, do so slowly! Too much too quickly can make you experience unpleasant digestive symptoms, especially gassiness and bloating…