Updated: Mar 18, 2021
Are you regularly consuming fermented foods such as kimchi, kefir, sauerkraut, sourdough bread, cheeses or even cured olives?
If they are still not part of your diet, you should probably make a conscious effort to get them more often. Health benefits of fermented foods include protection against infectious agents, a certain level of immunomodulatory effects, anti-allergic effects, anti-obesity and anti-diabetic effects, anti-anxiety and even damaged- muscle regenerating effects following exercise.
Fermented foods are only possible thanks to Lactic Acid Bacteria (LAB) ability to transform raw materials into edible and safe products with specific characteristics which dates back to thousands of years. “If you think about the history of humankind, earlier on, more than 60% of the food supply was fermented, due to the lack of means for preservation. On a daily basis, humans would have consumed many lactic acid bacteria”, explain researchers.
LAB are among the first living organisms on earth and are well adapted to both anaerobic and aerobic life conditions. They have developed the ability to recognise different types of sugars including fructose and glucose even before generating the ability to ferment lactose to lactate. That’s why they first colonised fruits and plants, and later cheese, wine and especially milk.
Lactic Acid Bacteria is actually a group of bacteria, which produce lactic acid as one of the main products of carbohydrate fermentation. LAB include not only the Lactobacillaceae family, well-known by the majority of people, but also many others such as Aerococcaceae, Carnobacteriaceae, Enterococcaceae, Leuconostaceae and Steptococcaceae. At present, it’s difficult to establish a clear differentiation between beneficial and pathogenic species, however Lactobacilli and Lactococci are generally regarded as safe.
Lactobacilli is one of the most studied bacteria, forming part of natural microbiota in animals and humans. They are found in many, if not most, fermented foods, but particularly in dairy fermented products, from which they get their name. They are even present in alcoholic drinks such as beer and wine and believed to contribute to the flavour of the product.
Interestingly, we still don’t really know if and how many live LAB from fermented foods actually reach the gut to join our gut microbiome. First, ingested LAB need to survive the chemical barrier of the digestive system, and then they have to compete with many different species to survive, before being able to exert their beneficial effect. LAB are actually considered a transient bacteria community, coming from an external source and closely interacting with the longer term members of our gut microbiome.
Recent study made a great attempt to analyse and compare genome-based differences between fermented food and human gut microbes on a large-scale level. They found that LAB strains (genomes) from food and/or supplements and gut are very closely related, providing more evidence that fermented foods may be a source for LAB in our guts. Although there is a link between the microorganism in our gut and those found in food, LAB species from food only partially match those in the gut. In addition, LAB species occur in low abundance in the human gut with the prevalence of Streptococcus thermophilus and Lactococcus lactis, particularly in westernized populations. Not surprising, these two species are widely present in dairy products and yoghurt that our modern society consume in large quantities.
It’s interesting that in the non-westernised population other LAB species are more common. And those are typically coming from raw vegetables, fermented vegetables and cereal based fermented foods. Traditional food fermentation is an extremely valuable heritage in most regions. Think about fermented soy in Japan, labneh in Middle East, fermented milks (ayran, kurut, koumiss) in Anatolia, fermented meat pastirma or basturma in Turkey and Caucasus region, Bulgarian fermented drink boza from cereals, fermented fish in Asia and many-many more – all contributing to gut bacteria diversity.
Perhaps habitual consumption of fermented foods and diets of specific geographic location determine specific LAB patterns and possible adaptation of the food LAB to the gut environment. But that would also suggest that some LAB may be rather stable than transient in nature, colonizing our guts with lasting effects. Some species such as Lactobacilli casei, Lactobacilli plantarum and Lactobacilli reuteri have been largely analysed due to their probiotic potential. But given their low prevalence in the human gut, perhaps they are unlikely to be part of long-term residents of the gut microbiota? Or maybe these bacteria may actually live in the gut epithelium, therefore undetectable in stool samples?
It’s fascinating, but very complex. We are still only at a discovery stage of LAB interaction with other microorganisms in the intestinal microbiome. And the notion of transient versus permanent is extremely important at evaluating the efficacy of microbial strain for gut health. Our current understanding is that probiotic supplements have a transient effect, which means that to achieve long term health benefits, one needs to take them permanently. On the other hand, fermented foods consumed on a regular basis may probably have much broader and persistent effects. Hopefully one day research will provide more light on this issue.
In the meantime let’s get pickled!