How Fermented Foods Calm the Mind

It has something to do with the limbic (or reptilian) brain.

Shin Jie Yong
Mar 24, 2020 · 5 min read
Image by 정훈 정 from Pixabay

“For those high in neuroticism, higher frequency of fermented food consumption was associated with fewer symptoms of social anxiety,” writes the associate professor of psychological sciences, Matthew Hilimire at College of William & Mary, United States. His study included 710 college students.

Food and Gut Microbiome

Within the microbial ecosystems in the gut, some species love fibers, some love proteins, some love sugars, some love fats, some love polyphenols, etc. As follows, foods we eat shape our gut microbiome (or microbiota). The gut microbiota, in turn, interacts with our physiology in such a way that confers symbiosis or dysbiosis.

All is good with symbiosis. It means that the gut microbiome is actively keeping the host healthy via its metabolite by-products such as anti-inflammatory butyrate and neuroactive peptides. It also means that beneficial gut microbes therein dominate and suppress the growth of harmful microbes.

Likewise, the opposite is true for gut dysbiosis, the loss of symbiosis. Gut dysbiosis has been shown, time and time again, to contribute to ill health, including neuropsychiatric disorders such as depression and anxiety.

Fermented Foods Are Gut-Friendly

Fermented foods include sauerkraut, kimchi, miso, soy sauce, tempeh, pickles, kombucha, kefir, cheese, and yogurt. Back to Hilimire’s study, the frequent intake of fermented foods (of any kind) seems to help neurotic youngsters to be less socially anxious. But how?

It would be helpful to first consider that neuroticism is a collection of neuropsychiatric symptoms characterized by depressed mood, anxiety, fear, frustration, etc. These sorts of symptoms have been associated with gut dysbiosis and can be improved by the consumption of probiotics, as seen in both human clinical trials and animal studies.

The fermentation process induced by lactic acid bacteria bestows fermented foods with beneficial microbes (probiotics), bioactive metabolites produced by the probiotics (biogenics), and substrates that nourishes good bacteria in the gut (prebiotics).

This three-in-one concoction— probiotics, biogenics, and prebiotics —present in fermented foods can ameliorate the gut dysbiosis of neurotic youngsters. The gut-brain axis is more harmonized as a result, and so is their mental health. As the study authors put it:

“Because these findings are consistent with results from previous preclinical and clinical trials suggesting that probiotics cause a reduction in anxiety symptoms, we hypothesize that the fermented foods assessed in the current study reduce anxiety because they contain probiotics.”

The Soothing Neurochemical

While increased consumption of fermented foods can help with anxiety and neuroticism, the underlying biological mechanisms are just as fascinating.

One of the biogenics found in fermented foods in high amounts is gamma-aminobutyric acid (GABA). Prebiotics of fermented foods also support the proliferation of GABA-producing bacteria in the gut. And probiotics present in fermented foods further fuel this effect.

The magic of GABA lies in the fact that it’s the main inhibitory neurotransmitter of the nervous system — meaning that it quells nerve activities. This is also why sleep medications act on GABA receptors.

GABA in the gut activates the vagus nerve, the primary nerve that is responsible for the rest-and-digest system. The vagus nerve calms the body and mind, which is why it has profound ramifications in wellness and health, as the renowned Markham Heid wrote in Elemental:

The Limbic Brain

The vagus nerve has neuronal connections to the gut. Upon sensing GABA in the gut — via its GABA receptors — the vagus nerve relays GABA signals to the brain, particularly the limbic (or reptilian) brain involved in emotional instincts and stress regulation.

The limbic brain houses the amygdala, which processes negative emotions such as fear, anger, and sadness. It’s an archaic brain structure that perceives threats before conscious awareness, making the host engage in fight-or-flight actions.

The limbic brain also comprises the hypothalamus and pituitary glands. Upon the recognition of a threat or other stressors, the hypothalamus secretes a chemical that tells the pituitary glands to secrete a hormone that, in turn, makes the adrenals produce cortisol. This hypothalamic-pituitary-adrenal (HPA) axis, therefore, triggers cortisol release that stimulates the fight-or-flight response.

Give mice fermented milk and researchers see that their vagus nerve lights up in a dose-dependent manner; their HPA axis is also suppressed as a result.

In anxious or neurotic individuals, it’s well-known that the amygdala and HPA axis are frequently in overdrive. Dampening these overactive areas can, therefore, be greatly helpful for their mental health and social functioning.

Direct Evidence from Clinical Trials

Compared to placebo, a 2-week consumption of fermented ginseng improved symptoms of depression in postmenopausal women. Similarly, fermented ginseng helped patients undergoing chemotherapy feel less anxious and afraid, relative to the control group.

Medical students experienced high levels of anxiety and had elevated salivary cortisol levels during exams. But this did not occur in those who were allocated to the experimental group of fermented milk drink for 8-weeks before the exam period. “Our results suggest that the daily consumption of fermented milk …[prevent] the onset of physical symptoms in healthy subjects exposed to stressful situations,” the Japanese researchers wrote.

A neuroimaging study showed that eating fermented yogurt for a month quells down emotional reactivity areas in the limbic brain, resulting in a more harmonized overall neural pattern in the brain versus baseline results and the control group. How did this happen? Based on reported findings in rodent studies, the authors commentated that “One might speculate that these changes are induced by altered vagal afferent signaling to the NTS.”

NTS is the nucleus tractus solitarius of the brainstem where the vagus nerve connects. And the NTS has direct projections to the limbic brain.

Fermented foods, thus, increase the GABA activity in the gut — via its probiotics, prebiotics, and biogenics — relaying this signal to the vagus nerve that sends calming signals to the limbic brain.

Feed Your Brain

Feed Your Brain explores the link between diet and mental…

Shin Jie Yong

Written by

Neurobiology MSc postgrad in Malaysia | 2x published academic author | 100+ articles on coronavirus | Freelance medical writer | shinjieyong@gmail.com

Feed Your Brain

Explores the link between diet and mental health, and how food influences brain function. How what you eat can change the way you feel, sharpen your focus, and affect your memory.

Shin Jie Yong

Written by

Neurobiology MSc postgrad in Malaysia | 2x published academic author | 100+ articles on coronavirus | Freelance medical writer | shinjieyong@gmail.com

Feed Your Brain

Explores the link between diet and mental health, and how food influences brain function. How what you eat can change the way you feel, sharpen your focus, and affect your memory.

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