Researchers at Benedictine University in Illinois conducted a randomized control trial to determine the effects on mood of consuming a vegetarian diet, compared with an omnivorous diet or a meat-restricted fish diet. Omnivorous diets are high in arachidonic acid (AA) and research has shown that high intakes of AA can promote changes in the brain that can disturb mood. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are fats found in fish which are thought to improve mood by opposing the negative effects of AA. This study randomly selected thirty nine omnivores and assigned them to either a group consuming meat, fish and poultry daily (OMN); a group consuming fish 3-4 times weekly but avoiding meat and poultry (FISH), or a vegetarian group avoiding meat, fish and poultry (VEG). Mood was tested using the Profile of Mood States questionnaire and the Depression Anxiety and Stress Scales. The study found that the VEG participants, who through the diet reduced their EPA, DHA and AA intakes, had mood scores that improved significantly after two weeks whereas OMN and FISH participants had mood scores that remained unchanged. In conclusion, the results of this study suggest that restricting meat, fish, and poultry may improve some domains of short-term mood states in modern omnivores.
Nutrition Journal 2012 Feb 14;11:9 (Beezhold et al.)