Fermented foods are a staple part of traditional diets all over the world and are increasingly popular thanks to their recognised links with digestive and mental health. The natural fermentation process enhances levels of probiotic bacteria, which in turn support the numbers and diversity of our own probiotic microbes. Fermented foods are also rich in fibres which act as prebiotics. Prebiotics feed and nourish our gut bacteria, enabling them to thrive and replicate.
The gut microbiome is made up of billions of different bacteria, yeasts, and fungi. These microbes communicate with the brain via the vagus nerve, in a bi-directional conversation known as the gut-brain-axis.
The diversity of these different microbes is key when it comes to mental health. Studies show that patients with depression have lower diversity and altered composition of their gut flora compared to healthy individuals.
Detrimental changes to the microbiome from stress, illness, antibiotics, or poor diet, can alter this diversity and increase production of inflammatory markers in the gut. These inflammatory chemicals have a major influence on neurological function. Inflammation is known to be affect mental health, and patients with inflammatory disorders are more prone depression.
How to ferment foods
Foods can be fermented in either of two ways. Firstly, through ‘wild’ fermenting where the microbes naturally present in foods are activated – sometimes through the addition of salt -and start fermenting. Both sauerkraut and kimchi are produced by wild fermentation.
The second method is via the addition of a starter culture, sometimes called a SCOBY. This stands for ‘symbiotic culture of bacteria and yeast’. A SCOBY is a collection of microbes that kickstart the fermentation process. Sourdough bread, kefir, kombucha, and yoghurt all require a SCOBY, and the starter cultures can last for years.
What are the benefits of fermented foods?
Every batch of fermented foods naturally has a slightly different profile of nutrients and bacteria, which makes it tricky to study them in controlled trials. Despite these practical difficulties, research has shown that fermented foods:
- Contain rich levels of probiotic bacteria and lactic acid that can reach the intestines and support the gut microbiota
- Contain prebiotics and vitamins
- Can support cognitive function and mood balance
- May be easier to digest thanks to lower levels of natural toxins and anti-nutrients like phytic acid. Fermented soybeans have lower levels of phytase inhibitors (substances that interfere with the actions of the phytase enzyme, which breaks down phytates found in plant-based foods, that block mineral absorption) whilst sourdough fermentation reduces levels of proteins that can trigger intolerance reactions for some people.
By supporting the gut microbiota, fermented foods are particularly beneficial for mental wellbeing and cognitive function. And you don’t have to eat masses of these foods to feel the benefits: including small amounts on a regular basis is a great way to nourish and support your gut microbiota.
Bonaz, B., Bazin, T., Pellissier, S. 2018. The Vagus Nerve at the Interface of the Microbiota-Gut-Brain Axis. Frontiers in Neuroscience 12:49 doi:10.3389/fnins.2018.00049
Dimidi, E., Cox, S.R., Rossie, M., Whelan, K. 2019. Fermented Foods: Definitions and Characteristics, Impact on the Gut Microbiota and Effects on Gastrointestinal Health and Disease Nutrients vol 11, 1806; doi:10.3390/nu11081806
Limbana, T., Khan, F., & Eskander, N. 2020. Gut Microbiome and Depression: How Microbes Affect the Way We Think. Cureus, 12(8), e9966. doi.org/10.7759/cureus.9966