The link between diet and mental health is becoming increasingly evident, although the biological mechanisms that explain this relationship are not yet fully defined. A new study now points to the gut microbiota as a key piece in this puzzle. The research, led by Rovira i Virgili University (URV), examined whether different dietary patterns are associated with specific profiles of gut microorganisms, and whether these profiles are, in turn, related to depressive symptoms. The journal MedComm has published the results of the study, which also involved the Institut de Recerca Biomèdica CatSud (IRB CatSud) and the Obesity Physiopathology Area of the CIBER network (CIBEROBN).
The study analyzed 644 older adults participating in the PREDIMED-Plus trial, all of whom had overweight or obesity and metabolic syndrome. The research team assessed their dietary habits, the composition of their gut microbiota using fecal samples, and the evolution of their depressive symptoms after one year of follow‑up. The aim was to explore whether the gut could act as a biological bridge between diet and mental health.
“We already knew that a higher‑quality diet is associated with better mental health, but the mechanisms were still unclear. Our results suggest that gut microbiota could be part of this explanation,” says Jordi Salas‑Salvadó, Professor of Human Nutrition at URV and coordinator of the study.
The researchers compared several dietary patterns that reflect common ways of eating. Four were considered higher‑quality patterns: the Mediterranean diet (standard version), the Mediterranean diet with an energy‑reduced approach, the DASH pattern—based on fresh, minimally processed foods and aimed at improving blood pressure—and a healthy plant‑based diet rich in fruits, vegetables, legumes and whole grains. Two lower‑quality patterns were also examined: an unhealthy plant‑based diet high in refined flours, sugary drinks and snacks, and a Western‑style diet characterized by more ultra‑processed foods, processed meats, sweets and low‑quality fats, along with a lower intake of fresh, fiber‑rich foods.
The results showed that individuals who more closely adhered to high‑quality dietary patterns tended to develop fewer depressive symptoms throughout the year. In contrast, greater adherence to lower‑quality patterns was associated with a less favorable evolution, with more depressive symptoms emerging.
The study also observed that diet leaves a measurable imprint on the gut. Healthier dietary patterns—especially the Mediterranean ones—were associated with a richer and more diverse microbiota, whereas lower‑quality patterns were linked to reduced microbial diversity. This is relevant because microbial diversity is often considered a marker of resilience and good functioning of the gut ecosystem.
Gut microbiota as a key mediator between diet and depression
The most innovative finding emerged when assessing whether gut microbiota could be involved in the link between diet and depression. The researchers found evidence that the gut microbiota may explain part of the observed effect of the Mediterranean diet on depressive symptoms—about 17% in the energy‑reduced version and around 31% in the standard version. In other words, part of the benefit associated with a Mediterranean dietary pattern may be related to the way this diet supports a healthier microbial profile.
“This study provides evidence that the profile of gut microorganisms may act as a mediator in the relationship between the Mediterranean diet and depressive symptoms. It is an important step toward understanding why some dietary patterns appear to be more protective than others, although further research is needed to confirm causality,” explains Adrián Hernández‑Cacho, the study’s lead author.
Taken together, the findings reinforce the relevance of the gut–brain axis and offer a plausible explanation for why improving diet quality may also benefit mental health. The authors highlight that this is one of the first international studies to provide evidence of a potential mediating role of gut microbiota in the relationship between dietary patterns and depressive symptoms, adding an essential piece to a rapidly evolving field. Still, the results do not yet establish a cause‑and‑effect relationship, and further studies in other populations and with more robust designs will be required to confirm these findings.
This multicenter study was led by Adrián Hernández‑Cacho and supervised by researchers Jordi Salas‑Salvadó and Jesús García‑Gavilán, all members of the Human Nutrition Unit within the Department of Biochemistry and Biotechnology at Rovira i Virgili University, in collaboration with other researchers from the PREDIMED‑Plus consortium. The team also belongs to the Biomedical Research Networking Center for the Physiopathology of Obesity and Nutrition (CIBEROBN) and the Institut de Recerca Biomèdica CatSud (IRB CatSud).
Reference: A. Hernández‑Cacho, J. Ni, J.F. García‑Gavilán, et al. “The Gut Microbiota as a Mediator in the Relationship Between Dietary Patterns and Depression.” MedComm 7, no. 2 (2026): e70562. https://doi.org/10.1002/mco2.70562
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