Stress, depression, diet, and the gut microbiota: human-bacteria interactions at the core of psychoneuroimmunology and nutrition

Abstract

Humans and their gut bacteria have evolved multiple ways to communicate with and regulate one another. Psychological stress and depression can promote consumption of highly palatable foods, influencing which gut bacteria thrive. Additionally, stress and depression can reshape the gut bacteria's composition through stress hormones, inflammation, and autonomic alterations. In turn, the gut bacteria release metabolites, toxins, and neurohormones that can alter eating behavior and mood. Some bacterial species may encourage dysregulated eating. The gut bacteria may also upregulate stress responsiveness and heighten the risk for depression, which probiotic supplementation may attenuate. This review focuses on human studies to address the bidirectional links among diet, stress, and the gut bacteria, and their impact on immune function and health.

Figure 1

Gut environment’s hypothesized role in psychoneuroimmunology. Depression and stress get under the skin via behavioral and physiological changes, including altered immune function. These adverse changes promote the survival and replication of pathogenic gut bacteria and weaken the gut barrier. Gut dysbiosis itself increases gut permeability, and it may also influence health behaviors like diet. These physiological and behavioral changes can ultimately further dysregulate key stress-responsive systems, including the immune, endocrine, and autonomic nervous systems, thereby fueling the chronicity of depression and stress.