Share on PinterestResearchers have discovered a connection between fermented foods and enhanced mental health. Marta Mauri/StocksyA new review suggests that consuming fermented foods may be linked to improved cognitive performance, primarily due to their capacity to influence the microbiota-gut-brain axis. Fermented foods help maintain a healthy and robust intestinal barrier, preventing the entry of bacteria and toxins into circulation and reducing the risk of leaky gut syndrome. The connection between the gut and brain is associated with various brain functions such as memory, cognition, anxiety, depression, and overall well-being. In recent years, extensive research has been dedicated to gut microbes, specifically examining their interaction with the brain, known as the microbiota-gut-brain axis. Given the known benefits of fermented foods for gut health, researchers wanted to investigate how these foods impact mental health. A recent review published in Neuroscience & Behavioral Reviews explored the various types of fermented foods, fermentation techniques, and their ability to influence the microbiota-gut-brain axis. Researchers also assessed the gaps in knowledge and challenges in conducting human studies. Examples of fermented foods include kimchi, sauerkraut, kefir, miso, tempeh, and yogurt. The review highlighted that fermented foods directly affect the enteroendocrine system, which influences hormones such as ghrelin, neuropeptide-Y, glucagon-like peptide 1 (GLP-1), and serotonin. Fermented foods are rich in prebiotics and probiotics, which increase the level of GLP-1. However, further research is required to comprehend how fermented foods affect appetite and hunger. Studies involving fermented dairy have produced mixed results on cognitive health in humans, while observational studies have linked fermented food consumption to changes in gut health and reduced anxiety. Dr. Nicole Avena, a nutrition consultant, assistant professor of neuroscience at Mount Sinai School of Medicine, and author of Sugarless, commented, “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. 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.” Avena explained that our gut contains numerous strains of bacterium and that various factors influence the species and diversity within the gut, starting from maternal health before birth to the current environment. “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,” she said. “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.” Dr. William Li, medical doctor and New York Times bestselling author of Eat to Beat Your Diet: Burn Fat, Heal Your Metabolism, and Live Longer, explained that the brain and gut are connected through various pathways involving nerves and circulation. “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. Li continued, “From the other end, substances from the brain can travel down nerves that begin in the brain and distribute like electrical wires to the gut. These signals can influence the gut bacterial ecosystem.” He also highlighted that substances produced by brain cells can enter the bloodstream from the brain and circulate to the gut, affecting the gut microbiome. “While research on exact bacteria-to-brain/brain-to-bacteria effects are still in their infancy, this gut-brain connection is associated with a wide variety of brain functions such as memory, cognition, anxiety, depression, and overall mental health and wellness,” Li stated. “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.” Li explained that fermented foods contain bioactives from the original food itself, healthy bacteria (probiotics), and the metabolites created by these bacteria (post-biotics). These components contribute to the activity of the gut microbiome, either by promoting healthy gut bacteria or by directly impacting the gut bacteria or their products. “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. The review addresses many of the limitations and gaps in current research on the gut-brain connection. For instance, “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. Additionally, “clinical studies of fermented foods may not capture sex-specific differences or account for the diversity of diet, lifestyle, behavioral, and genetic factors in their subjects,” he added. The generalization of findings is also limited by how fermented foods differ across regions by how they are produced, and the environment in which they are stored and consumed. Despite these limitations, the review presents a compelling case based on scientific evidence that gut health influences brain health, which in turn affects mood and behavior, Li added. It’s worth noting that this review lacks original data since it is a narrative review. Although the authors point out the poor methodology in some of the individual studies they cite, such as inadequate controls, there is no formal scoring of the research quality of individual papers. Avena emphasized the need for more evidence on the exact effects of fermented foods on direct human microbiome and neurotransmitter research.
