Why do I eat fermented foods?

John Leech, University College Cork
Fermentation is almost as old as agriculture itself, with fermented foods dating back at least 9000 years. The earliest evidence we have for the production of these foods comes from Jihau in China, where an alcoholic drink, Mead, was produced in clay pots. The Egyptians were the first to manufacture beer. Beer provided protein and vitamins to its early consumers, and it was also safer to drink than water in many cases. It was so important to Egyptian culture that it is estimated that they drank on average 2.5 litres a day. Today, there are over 5000 varieties of fermented foods worldwide.
I began studying these foods almost 4 years ago as a PhD student. I have learnt a lot about these foods in that time, including how to make some of them. At the beginning of my studies, I was lucky enough to partake in a fermented food cookery course in Ballymaloe Cookery school, where the extremely knowledgeable chefs taught me (and others) how to produce a variety of these foods. Since then, making fermented foods has become a part of my daily routine. My kefir requires my attention daily, whereas my kombucha and sauerkraut can be produced far more occasionally. I often dabble in kimchi, villi, fermented salsa and from time to time I make my own mead. I have become much more aware of these foods through my studies, and they have become an important part of my life, both as a subject to study, but also as food to enjoy. Unlike ancient Egyptians, I do not need beer to get protein or vitamins (I often use it as an excuse though). Safe water is readily available.  So, why do I spend so much time away from the lab producing and consuming them?
Fermented foods, particularly artisanal fermented foods have remerged as popular foods in western cultures. I`m usually the last to know about a trend, and if it were not for my studies, I would probably still be oblivious. Part of the reason for their re-emergence is their perceived benefits to health. Microbiome research has exploded in recent years, and many illnesses are associated with microbiome health. The gut microbiome is particularly important. We know that the diversity (the number of species), residing in the gut, contribute towards health. The more the better.
Fermented foods are full of live microorganisms. It is widely perceived that these live foods can benefit our own gut flora. On top of the direct actions of these fermenting microbes on our own gut health and diversity, the vitamins and other health promoting products that these microbes produce in the foods can also be beneficial. But what research is available to back up these beliefs that are driving the fermented food trend?
At the beginning of the 20th century, a Russian scientist, Ellie Metchnikoff, attributed the long lives of Bulgarian peasants to the consumption of fermented milk. Despite the early interest in fermented foods and their benefits to health, it is only recently that scientific studies have examined the potential of these foods. Currently, we do not know enough about these foods and their interaction with consumers to make strong health claims. There are several promising studies on a small number of these foods (small relative to the 5000 varieties) indicating that they could have an important role to play as we strive to find healthier ways to live. Evidence is gathering, and two recent studies have taken another important step in exploring these foods and answering our questions.
The first study explores the microbiota-gut-brain axis (Study 1). The microbiota-gut-brain axis is the two directional communication between the brain and the gut microbiome. This axis has been shown to be very important in mood, mental health and other brain associated disorders such as Alzheimer’s disease and dementia. The recent study from the APC Microbiome Ireland (APC) SFI Research Centre in Cork has shown the potential of kefir, a fermented milk drink, to change specific aspects of the microbiota-gut-brain axis. The experiment demonstrated that by feeding mice with 2 different milk kefirs, mice showed improvements in several key aspects. A key feature of depression is a reduction in reward-seeking behaviour. Mice fed with one of these kefirs showed an increase in reward-seeking behaviour. These results are promising in terms of finding new treatments for depression. The same kefir also reduced the stress levels of the mice. A second kefir improved the mice’s contextual memory and was also shown to stimulate the immune system. What is most interesting from the consumers point of view, is that both kefirs were able to provide benefits, but both had exclusive effects. However, both kefirs did change the gut microbiome of the mice, increasing the capacity of their microbiomes to produce GABA, a chemical that is important for mental health.
The second study, involving the APC and the European MASTERs project, addressed another fundamental question regarding fermented foods. Do the microbes in fermented foods colonise the gut? Fermented foods are often considered as probiotic and good for gut health. Unfortunately, unless a known strain of a probiotic is added to a fermented food and shown to persist in the final product in adequate amounts, then the food does not contain microbial strains that can be scientifically defined as probiotics. It is not because these foods do not contain beneficial microbes, it is because for something to be defined as probiotic, it must undergo rigorous clinical trials.
Gut health is a tricky area of research. There is no specific configuration of a microbiome that we can say for sure indicates a healthy microbiome. However, increased diversity (higher number of species) can be indicative of a healthy microbial ecosystem. Although there have been many animal studies exploring the effects of fermented foods on the gut microbiome, human studies are almost lacking. Animal studies are good indications of what might occur in people, but human trials are necessary to be sure of any effect. A handful of exciting studies have shown that consuming fermented foods can influence the human microbiome. But the list of foods contained in these studies is limited to sauerkraut, fermented milk and kimchi. Research needs to show an effect of a broader assortment of fermented foods, on the human microbiome. Then, perhaps, we can be more certain that fermented foods are beneficial to the gut microbiome.
In this second study, researchers have provided more evidence to support the belief that these foods can indeed influence our microbiomes (study 2) The study looked at species of microbes present in a global assortment of fermented foods. It compared these microbes to the microbes in almost 10,000 human microbiomes from around the world. Specifically, it looked at lactic acid bacteria. Lactic acid bacteria are a family of bacteria, found in most fermented foods and, also in human microbiomes. Lactic acid bacteria represent the majority of probiotic species that are currently in use and have many functional benefits for human health, flavour production and food production.
By examining the similarity between the microbes found in fermented foods and those residing in the human gut, researchers were able to conclude that fermented foods were likely sources of important human gut microbes. The study was even able to reflect the dietary patterns of some populations. Certain species of microbes present in yoghurt showed up in Westernized microbiomes, but not in Chinese microbiomes. The Chinese population generally consume less dairy.  By examining such a large dataset, researchers were able to see these patterns that would otherwise not emerge from smaller scale local studies.
How do I know the kefir that I make at home has any of the above benefits? Well, I do not know if my specific kefir has any benefits. Or my sauerkraut. Or my kombucha. So, why do I produce and consume my own foods? The variability between batches of fermented foods means it will be next to impossible to say with certainty that a specific batch has certain health attributes. But there are more and more studies emerging showing various health benefits from a variety of these foods, and that is why I will keep making them and eating them. Our ancestors were exposed to billions of microbes in their homes and in their foods. Most of my food comes from a supermarket. By inhibiting microbial growth in these foods to extend shelf life, or sterilising them for safety, most of my food is devoid of microbial diversity. By sanitizing my home and living space, furnished with unnatural materials, and eating these relatively sterile foods, my microbiome has become less diverse than my ancestor’s microbiomes were for hundreds of thousands of years. Even nowadays, populations living more traditional lifestyles have greater gut diversity than those of us in the industrialised world. We now know that industrialised gut microbiomes are less diverse than the microbiomes of more traditional lifestyles. Perhaps fermented foods can offer safe exposure to billions of microbes that we have excluded from our lifestyle in modern times. Diversity matters, another reason why I eat fermented foods.
Want to learn more? Listen to this podcast for which I was recently interviewed: https://www.thenakedscientists.com/podcasts/naked-genetics/fermented-foods-real-deal