Fermented foods are not included in the recently revised ISAPP definition of probiotics, since the bacteria they contain are uncharacterized. But scientists are nevertheless studying how these foods may affect health, including brain function.
This blog post covers a correlational study on fermented food consumption and social anxiety. The study found that young adults who consumed more fermented foods and fruits/vegetables, and those who engaged more frequently in exercise, had lower levels of social anxiety. Young adults who already expressed higher levels of neuroticism had less social anxiety when they consumed fermented foods.
Despite the significant limitations of this study — chiefly, that causality cannot be inferred — its findings warrant further investigation. With further data, low-risk interventions such as fermented food consumption could be used to complement existing clinical strategies for lowering anxiety.
Hilimire MR, et al. (2015) Fermented foods, neuroticism, and social anxiety: An interaction model. Psychiatry Research doi: 10.1016/j.psychres.2015.04.023