In a recent review published in the journal Neuroscience & Biobehavioral Reviews, researchers from Ireland explored the diversity of fermented foods, their sources, and fermentation techniques while examining their capacity to impact the microbiota-gut-brain axis. Additionally, they identified knowledge gaps and challenges in studying the mental health benefits of specific fermented foods and proposed solutions to further understand their therapeutic potential.
Study: Fermented Foods: Harnessing Their Potential to Modulate The Microbiota-Gut-Brain Axis for Mental Health. Image Credit: Molishka / Shutterstock
Background
Microbes colonizing the gut serve as a vital mediator in the microbiota-gut-brain axis, connecting the body’s external signals and intrinsic functions and communicating continuously with the central nervous system. Various factors, including diet, influence the gut microbiota and impact the intestinal, immunological, and neural components of the microbiota-gut-brain axis. Recent advances highlight the potential of microbiota-targeted dietary interventions, such as probiotics, prebiotics, and fermented foods, to enhance mental health by modulating the gut-brain axis.
Fermented foods were historically used for prolonging storage and enhancing flavor. They are diverse, categorized by substrates including cereal, dairy, meat, fish, vegetable, and legume, each undergoing unique fermentation processes. These foods harbor a rich microbial community influenced by substrate type, geographical location, pH, and preparation methods, offering potential probiotics, bioactive peptides, phytochemicals, and vitamins. Researchers continue to investigate fermented foods due to their ability to shape gut microbiota composition, produce beneficial metabolites, and modulate pathways connecting the gut and brain, providing a promising avenue for dietary interventions.
The present review explores the mental health benefits of fermented foods, examining their impact on the microbiota-gut-brain axis and discussing the challenges in preclinical and human studies.
Fermented food and the microbiota-gut-brain axis
Fermented foods influence the microbiota-gut-brain axis through immune modulation, barrier integrity, and neuroendocrine regulation. Microbes and metabolites from fermented foods interact with receptors, impacting immune responses. Fermented foods enhance intestinal and blood-brain barrier integrity, potentially mediated by microbial metabolites. They also influence the hypothalamic-pituitary-adrenal (HPA) axis and serotonin levels. Preclinical and human studies reveal diverse immunomodulatory effects of fermented foods, highlighting the need to explore their complex interactions with the microbiota-gut-brain-immune axis further.
Fermented foods exert profound effects on the gut-brain axis through modulation of the enteroendocrine system (EES), influencing gut hormones like serotonin, neuropeptide-Y, glucagon-like peptide 1 (GLP-1), ghrelin, and somatostatin. These hormones regulate motility, appetite, and insulin release, impacting feeding behavior. Fermented foods, rich in prebiotics and probiotics, shape the gut microbiota and enhance the production of gut hormones, particularly GLP-1. However, studies on the impact of fermented foods on satiety are inconclusive, with variations in hormone release observed. Additionally, fermented foods may alter ghrelin and leptin levels, contributing to appetite regulation. Understanding these complex interactions is crucial for harnessing the potential health benefits of fermented foods.
Preclinical and clinical landscape
Fermented foods impact gut-brain communication pathways, influencing immune responses, gut microbiota, microbial metabolites, and the enteric nervous system. Preclinical models, including drosophila, zebrafish, mice, and pigs, reveal behavioral improvements and microbiota alterations with fermented dairy, soy, sugar-based products, and other substrates. Human studies on fermented dairy show mixed cognitive effects, while observational studies link fermented food consumption to altered gut profiles and reduced anxiety. Fermented soy products, particularly isoflavones, may benefit cognitive function in women, contrasting with negative associations for tofu consumption. A previous meta-analysis suggests that fermented foods hold promise for cognitive outcomes.
Future trends and challenges
Standardizing fermented foods is challenged by diverse microbial communities influenced by factors like geography, production scale, and substrate type. Environmental conditions, fermentation duration, salinity, pH, moisture, and ripening time contribute to complexity. Regulatory guidelines offer limited insights, requiring cultural sensitivity. ‘Omics’ techniques aid understanding and data archiving, but the vast diversity of fermented foods demands further exploration for effective standardization, considering both bioactive potential and cultural preservation. Setting up human studies for fermented food interventions presents challenges like accounting for controls, emphasizing the need for unfermented controls in assessments. Accurate measurement of fermented food intake is hindered by the diversity of foods recommended, requiring detailed methods like 24-hour food recalls and food diaries. Biomarkers associated with fermented food consumption offer precise measurement, utilizing advancements like plant metabarcoding for unique fingerprints. Employing suitable microbiome capture methods involves choosing high-resolution techniques like shotgun metagenomics over 16S rRNA (short for ribosomal ribonucleic acid) sequencing.
Conclusion
In summary, the present study reviews the substantial impact of fermented foods on health, leveraging diverse microbial strains, metabolites, and bioactive compounds to optimize neural and mental health benefits. It emphasizes the need for additional human studies, particularly with unfermented controls, to comprehensively identify and understand the beneficial impacts of fermented foods on the microbiota-gut-brain axis. Despite challenges, fermented foods emerge as pivotal components in the evolution of microbiota-based therapeutics for mental health.