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

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.