Fermented foods and beverages have been a key staple of many cultures around the world for thousands of years. As well as preserving food and adding flavour, fermentation gives the foods additional nutritional value and medicinal properties. Fermented foods were traditionally known to work on the senses and they are the most important source of mood stabilising nutrients, offering profound benefits for cognitive and overall health. Our ancestors knew the beneficial effects of fermented foods on the body including mental function and wellbeing- even the name Kefir was derived from the Turkish word for ‘good feeling’. As our diets have radically changed and we are no longer consuming these traditional dietary staples like fermented foods, and mental health disorders which were considered an anomaly in ancestral communities have risen to an all-time high (1).
We often think of fermented foods and their benefits for gut health, and increasingly research has highlighted the link between the gut and the brain. A growing body of literature speculates that alterations in the gut microbiome may play a key pathophysiological role in human brain diseases including autism, anxiety, depression and chronic pain (2). Emerging studies have shown that in a number of mental health conditions where the intestinal barrier might be compromised- this could be due to stress, or to the switch from traditional dietary practices to a western diet high in fat, sugar and low nutrient value food- creating a more porous lining and the likelihood of an inflammatory microbiome (1).
There is a complex communication and signalling system that links our Central Nervous System (including our brain) and our Enteric Nervous System (including our GI tract) known as the Brain-Gut axis. The gut microbiome plays a critical role in regulating normal function of this axis. There are many potential mechanisms by which the microbiome influences brain activity including: producing signalling molecules (amino acid metabolites, short chain fatty acids and neuroactive substances), influencing neurotransmitter production (imbalances of which are linked to depression), activating neural pathways, and limiting inflammatory response which has been linked to many cognitive conditions from autism to depression (3).
Traditional diets rich in fermented foods with antioxidants and anti-inflammatory properties offered neuroprotective effects that helped to support cognitive function by increasing protein quality, increasing bioavaiblity of mood-regulating B-vitamins, vitamin D, magnesium and zinc, providing strong antioxidant protection and producing compounds like the calming neurotransmitter GABA which is implicated in poor mental health (1) .
There is increasing evidence highlighting how regular consumption of fermented foods can have mental health benefits backing up what our ancestors knew all along: One study showed how fermented soymilk intake improved learning and memory, another showed that high consumption of tempeh had a positive impact on memory and other studies have linked consumption of fermented foods to improved mood and cognition (1). Another study showed that consumption of a fermented dairy product for four weeks affected activity of brain regions controlling central processing of emotions and sensation (3). Consuming fermented foods and herbs can help restore a healthy microbiome, normalise the gut-brain axis and optimise mental health.
The consumption of fermented foods, rich in beneficial bacteria, can help replenish the gut microbiome and reduce intestinal permeability. Fermentation modulates the chemical constituents, improving the activity and bioavailability of foods and herbs. A number of studies have reported the fermentation process as enriching bioactive peptides and creating phytochemicals which may enhance their neuroprotective effects (4). Fermentation also increases bioavailability, and modulates the release of neurotransmitters such as BDNF, GABA and serotonin which are reported to be involved in learning and memory (4).
A return to ancestral fermented food consumption could be an effective intervention for mental health disorders. There are many foods and herbs within traditional dietary patterns that when fermented offer excellent cognitive health benefits. One of the most effective herbs for the brain is Holy Basil which contains compounds that balance stress hormones and support the nervous and immune system. Studies have found it decreases stress hormone levels, in particular corticosterone, the reduction of which improves cognitive functioning. Lions Mane mushroom also supports brain function as it stimulates the production of nerve growth factor (NGF) which helps to maintain the neurons, which are brain cells responsible for helping us to process and transmit information, aiding learning and memory. Traditionally consumed foods and herbs like Holy Basil, Gotu Kola, Turmeric and Green Tea are packed with antioxidants and offer much promise for supporting cognitive health, and their enhanced bioavaiblity via fermentation may be an important factor to use these food and herbs as medicine (1).
Fermentation offers substantial benefits to cognitive health, from the magnified antioxidant and anti-inflammatory activity, reduction of intestinal permeability, positive influence on nutritional status, direct production of GABA and other bioactive chemicals (1). We are only just beginning to scratch the surface in our understanding of the relationship between the microbiome and brain health, but fermented foods may be the key link in the gut-brain axis and overall cognitive health.
1: Selhub EM, Logan AC, Bested AC. Fermented foods, microbiota, and mental health: ancient practice meets nutritional psychiatry. Journal of Physiological Anthropology. 2014;33(1):2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3904694/
2: Reddy, BL and Saier, MH. Autism and Our Intestinal Microbiota. Journal of Molecular Microbiology and Biotechnology. 2015;25 51-55. https://www.karger.com/Article/FullText/375303
3: Tillisch K, Labus J, Kilpatrick L, et al. Consumption of Fermented Milk Product With Probiotic Modulates Brain Activity. Gastroenterology. 2013;144(7):10.1053/j.gastro.2013.02.043. doi:10.1053/j.gastro.2013.02.043.
4: Kim B, Hong VM, Yang J, et al. A Review of Fermented Foods with Beneficial Effects on Brain and Cognitive Function. Preventive Nutrition and Food Science. 2016;21(4):297-309. doi:10.3746/pnf.2016.21.4.297.