Numerous studies on gut bacteria have been conducted recently, with an emphasis on their interactions with the brain (the microbiota-gut-brain axis). Researchers were interested in investigating the effects of fermented foods on mental health because they are particularly well-known for their benefits to gut health.
A recent analysis examined the many forms of fermented foods, fermentation processes, and their potential impact on the microbiota-gut-brain axis in Neuroscience & Behavioral Reviews. Scholars have examined gaps in knowledge and difficulties in carrying out investigations with humans.
Fermented foods include, for example:
Sauerkraut, kefir, miso, tempeh yogurt, and kimchi
The review pointed out that the enteroendocrine system, which regulates hormones like ghrelin, neuropeptide-Y, glucagon-like peptide 1 (GLP-1), and serotonin, is directly impacted by fermented foods. Foods that have undergone fermentation are rich in probiotics and prebiotics, which raise GLP-1 levels. To fully understand how fermented foods impact hunger and appetite, more research is necessary.
While observational studies link the use of fermented foods to improvements in gut health and a reduction in anxiety, human research on fermented dairy have yielded conflicting results regarding cognitive health.
“We know from previous studies that there is a proven gut-brain axis and that this, therefore, links diet directly to the brain and its behavior based on the health of our microbiota,” said Dr. Nicole Avena, nutrition consultant, assistant professor of neuroscience at Mount Sinai School of Medicine, visiting professor of health psychology at Princeton University, and author of Sugarless.
“I think this review does a good job at showing the history behind fermentation and the physiology behind how it became known as a superfood for gut and brain health,” she said.
Describing the Connection Between the Brain and the Gut
According to Avena, there are hundreds of distinct strains of bacteria in our stomach. Because so many various factors influence the species and variety within the stomach, each person’s microbiome is unique. These variables range from the prenatal health of the mother to the contemporary surroundings.
“What makes food such an important part of gut health is that it is a tangible method we can use to diversify and strengthen (or weaken) our gut flora,” said Avena. “The gut-brain axis has been linked to the health and diversity of our microbiome – meaning the less diverse the diet, the more mental and brain health can suffer. We know these bacteria help with digestion, absorption, and byproduct of nutrients that can directly affect our mental health.”
According to Dr. William Li, a physician and the New York Times bestselling author of Eat to Beat Your Diet: Burn Fat, Heal Your Metabolism, and Live Longer, there are numerous routes involving neurons and circulation that connect the brain and intestines.
“Substances produced in the gut by bacteria can travel or send signals up large nerves, such as the vagus nerve, directly to the brain — triggering different brain activities that can alter mood, behavior, memory, and cognition,” he said.
According to Dr. William Li, a physician and the New York Times bestselling author of Eat to Beat Your Diet: Burn Fat, Heal Your Metabolism, and Live Longer, there are numerous routes involving neurons and circulation that connect the brain and intestines.
In terms of circulation, microorganisms in the stomach have the ability to create chemicals that enter the bloodstream and travel straight to the brain. Li also mentioned that chemical signals generated by brain cells have the ability to go from the brain to the gut via the bloodstream, where they can impact the gut microbiome.
“There are many compelling correlations showing that dysbiosis, or abnormal gut microbiome composition, is associated with depression, anxiety, dementia, Parkinson’s disease, and other neurodegenerative disorders,” he added.
The Impact of Fermented Foods on Mental Health
Foods that have undergone fermentation retain both beneficial bacteria known as probiotics and their byproducts, called post-biotics, as well as bioactives from the original food itself, such as dietary fiber and polyphenols.
According to Li, these elements of fermented foods either directly support the gut bacteria or their products or feed good gut bacteria, so promoting their activity on the gut-brain axis and enhancing the activity of the gut microbiome of the person consuming the food.
“The net effect is to contribute to a healthier gut bacteria ecosystem that activates brain pathways. There are many still unanswered questions about the gut-brain connection, but this is the current view based on research in the lab as well as in human studies,” he said.
Why Further Research is Required
Numerous knowledge gaps and shortcomings in the field’s present research on the gut-brain link are addressed in this review.
For example, “studies involving single bacteria do not capture the full extent that fermented foods play on the gut-brain axis because of the plethora of bacteria, metabolites, and other small molecules present in food that may be playing important roles,” Li said.
Furthermore, he said, “The diversity of diet, lifestyle, behavioral, and genetic factors in their subjects may not be accounted for or captured in clinical studies of fermented foods.”
The fact that fermented foods vary from location to region in terms of production methods and storage and consumption conditions further restricts the generalizability of research findings. Notwithstanding these drawbacks, Li continued, the review presents a strong case supported by scientific data showing gut health affects brain health, which in turn affects mood and behavior.
Avena stated, “I believe that one of the only significant limitations is the small number of studies that use human subjects.”