In a recent review published in the magazine Neuroscience and Biobehavioral ReviewsResearchers from Ireland explored the diversity, sources and fermentation techniques of fermented foods while studying their ability to influence the microbiota-gut-brain axis. Additionally, they identify knowledge gaps and challenges in researching the mental health benefits of specific fermented foods and suggest solutions to further understand their therapeutic potential.
Study: Fermented foods: Harnessing their potential to modulate the microbiota-gut-brain axis to promote mental health. Image credit: Molishka/Shutterstock
Microorganisms colonizing the gut are important mediators in the microbiota-gut-brain axis, connecting the body’s external signals and intrinsic functions and continuously communicating with the central nervous system. Various factors, including diet, influence the gut microbiota and affect the intestinal, immune, and neural components of the microbiota-gut-brain axis. Recent advances highlight the potential of dietary interventions targeting the microbiota (e.g., probiotics, prebiotics, and fermented foods) to enhance mental health through modulation of the gut-brain axis.
Fermented foods have historically been used to extend storage time and enhance flavor. They are diverse and classified by substrate, including grains, dairy, meat, fish, vegetables and legumes, each undergoing a unique fermentation process. These foods harbor rich microbial communities, influenced by substrate type, geographical location, pH and preparation method, providing potential probiotics, bioactive peptides, phytochemicals and vitamins. Researchers continue to study fermented foods because of their ability to shape gut microbiota composition, produce beneficial metabolites, and modulate pathways connecting the gut and brain, providing a promising avenue for dietary intervention.
This review explores the mental health benefits of fermented foods, examines their impact on the microbiota-gut-brain axis, and discusses challenges in preclinical and human studies.
Fermented foods and the microbiota-gut-brain axis
Fermented foods influence the microbiota-gut-brain axis through immunomodulation, barrier integrity, and neuroendocrine regulation. Microorganisms and metabolites in fermented foods interact with receptors and influence immune responses. Fermented foods can enhance intestinal and blood-brain barrier integrity, possibly mediated by microbial metabolites. They also affect the hypothalamic-pituitary-adrenal (HPA) axis and serotonin levels. Preclinical and human studies have revealed diverse immunomodulatory effects of fermented foods, highlighting the need to further explore their complex interactions with the microbiota-gut-brain-immune axis.
Fermented foods have profound effects on the gut-brain axis by regulating the enteroendocrine system (EES), affecting intestinal tract proteins such as serotonin, neuropeptide Y, glucagon-like peptide 1 (GLP-1), ghrelin, and somatostatin. hormone. These hormones regulate movement, appetite, and insulin release, affecting eating behavior. Fermented foods rich in prebiotics and probiotics can shape the gut microbiome and enhance the production of gut hormones, especially GLP-1. However, research on the effects of fermented foods on satiety is inconclusive, and changes in hormone release have been observed. Additionally, fermented foods may alter ghrelin and leptin levels, aiding in appetite regulation. Understanding these complex interactions is critical to harnessing the potential health benefits of fermented foods.
Preclinical and clinical situations
Fermented foods influence gut-brain communication pathways, affecting immune responses, gut microbiota, microbial metabolites, and the enteric nervous system. Preclinical models including Drosophila, zebrafish, mice, and pigs have revealed behavioral improvements and microbiota alterations on fermented dairy products, soy, sugar-based products, and other substrates. Human studies of fermented dairy products have shown mixed cognitive effects, while observational studies have linked fermented food intake to altered gut conditions and reduced anxiety. Fermented soy products, especially isoflavones, may benefit cognitive function in women, while tofu consumption may have negative effects. A previous meta-analysis showed that fermented foods hold promise for improving cognitive outcomes.
Future trends and challenges
Standardization of fermented foods faces the challenge of diverse microbial communities influenced by factors such as geography, production scale, and substrate type. Environmental conditions, fermentation duration, salinity, pH, humidity and ripening time all affect complexity. Regulatory guidance provides limited insights and requires cultural sensitivity. ‘Omic’ technologies can aid understanding and data archiving, but the vast diversity of fermented foods requires further exploration of effective standardization, taking into account both bioactive potential and cultural preservation. Establishing human studies of fermented food interventions presents several challenges, such as accounting for controls, emphasizing the need for unfermented controls in evaluations. The diversity of recommended foods hinders accurate measurement of fermented food intake, requiring detailed methods such as 24-hour food recalls and food diaries. Biomarkers related to fermented food consumption utilize advanced technologies such as phytobarcoding to provide precise measurements to obtain unique fingerprints. Employing appropriate microbiome capture methods requires choosing high-resolution techniques such as shotgun metagenomics rather than 16S rRNA (short for ribosomal ribonucleic acid) sequencing.
In conclusion, this study reviews the significant impact of fermented foods on health, utilizing different microbial strains, metabolites and bioactive compounds to optimize neurological and psychological health benefits. It highlights the need for more human studies, particularly unfermented controlled studies, to fully identify and understand the beneficial effects of fermented foods on the microbiota-gut-brain axis. Despite the challenges, fermented foods are emerging as a key component in the development of microbiota-based therapies for mental health.