In January 2019 researchers from Iran published the results of their review of the medical scientific literature to assess the association between diet and state of mind. A total of 18 studies were included in their review. Results showed that although the findings between studies were not consistent, it appeared that the DASH, vegetable-based, glycemic index-based, ketogenic and Paleo diets could improve mood more than the others. Further research is therefore required before drawing a firm conclusion as to whether there is a link between diet and mood.
Arab A et al. The association between diet and mood: A systematic review of current literature. Psychiatry Res. 2019 Jan;271:428-437