Growing evidence highlights the importance of the gut-brain axis. It’s long been known that what we eat affects our mental health, but new research led by the University Rovira i Virgili (URV) has delved deeper into the biological mechanisms behind this connection. Understanding this link is crucial as mental health conditions continue to impact individuals globally.
Researchers analyzed different dietary patterns and their associated gut microorganisms, revealing notable similarities. They confirmed that greater adherence to the Mediterranean diet is linked to fewer symptoms of depression, according to Adrián Hernández-Cacho, a member of the Human Nutrition Unit at the URV’s Department of Biochemistry and Biotechnology and the study’s lead author. The findings were recently published in the journal MedComm.
The study followed 644 adults with overweight or obesity and metabolic syndrome for one year. All participants were residents of Spain and part of the PREDIMED-Plus trial. Throughout the year, researchers tracked their dietary habits—reviewing intake of 144 different foods—as well as their gut microbiota through stool samples and their depressive symptoms using a validated international tool.
The results showed that individuals who more closely followed dietary patterns of higher quality—including diets like the Mediterranean diet, designed to lower blood pressure, or those rich in fruits, vegetables, legumes, and whole grains—reported fewer depressive symptoms.
Conversely, those who consumed diets lower in nutritional quality, characterized by refined flours, pro-inflammatory foods, sugary drinks, and processed or low-quality fats with limited fresh produce, experienced less favorable outcomes and more depressive symptoms.
A Footprint in the Gut
“Current evidence suggests that chronic low-grade inflammation, oxidative stress, impaired antioxidant defense mechanisms, and insulin resistance can contribute to the development of psychiatric disorders, including depression,” the published study explains. It further notes that “fruits and vegetables are rich in dietary fiber, phytochemicals, and micronutrients with antioxidant properties, which can help reduce oxidative stress and inflammation, thereby decreasing the risk of depressive symptoms.”
Researchers found that diet leaves a footprint in the gut, with healthier eating patterns associated with a richer and more diverse microbiota, while less healthy patterns correlated with reduced diversity. This is significant because microbial diversity is often considered an indicator of resilience and proper functioning of the gut ecosystem.
Based on these observations, the researchers suggest that the gut microbiota may explain some of the benefits observed between the Mediterranean diet and depressive symptoms. “This study provides evidence that the profile of microorganisms in the gut can act as a mediator in the relationship between the Mediterranean diet and depressive symptoms,” Hernández-Cacho emphasized.
“This is an important step in understanding why some dietary patterns appear more protective than others, although further research is still needed to confirm causality,” the expert added. He cautioned, yet, that “depression is a multifactorial disorder and not everything related to depression can be explained by the microbiota.”
The study’s authors acknowledge that there is still limited evidence in this field and that it is too early to establish a cause-and-effect relationship. They hope to replicate this study in other populations to witness if the same findings are confirmed. If confirmed, they foresee potential applications in dietary intervention and as a valuable complement to psychotherapy. “this will help provide evidence to prescribe more behavioral therapy, based on diet or exercise,” Hernández-Cacho concluded.
