Dietary Patterns, Gut Microbiome, and Mental Health in Adults: Investigating the Gut–Brain Axis and Its Implications for Personalized Nutrition

Background The influence of dietary intake on gut microbiota profiles can impact psychological well-being via the gut–brain axis. However, there is limited literature examining the complex interrelationships among these variables. Aim This integrative review aims to examine the relationships between dietary patterns, gut microbiome profiles, and mental health status among adults and explore their implications for personalized nutrition. Methods The integrative review methodology followed the five-stage framework developed by Whittemore and Knafl. Searches were conducted in PubMed/MEDLINE and Google Scholar. Articles involving adult participants and examining dietary patterns, dietary intake, or dietary components in relation to gut microbiome profiles and/or mental well-being were considered. Randomized controlled trials, observational studies, qualitative research, and other relevant literature were eligible for inclusion. Methodological quality was assessed using design-specific critical appraisal tools. The Cochrane Risk of Bias 2 tool was used for randomized controlled trials, while appropriate validated appraisal tools were used for observational studies according to study design. Summary Healthier dietary patterns, particularly Mediterranean and fiber-rich diets, have been associated with favorable gut microbiome characteristics and better psychological health. Conversely, Western-style and highly processed diets have been associated with poorer psychological outcomes, gut dysbiosis, and inflammation. Potential biological mechanisms include short-chain fatty acid (SCFA) synthesis, intestinal permeability, immune responses, inflammation, hypothalamic pituitary adrenal (HPA) axis activity, neurotransmission, and vagus nerve activity. Dietary patterns, gut microbiome profiles, and psychological health appear to be interconnected through multiple biological pathways. Integrating dietary, microbiome, and psychological data may provide a promising foundation for personalized nutrition; however, further research is needed to establish causality and practical applications.