Preliminary evidence that vegetarian diet improves mood

Background: An omnivorous diet is typically higher in fat and protein, and contains less healthy fatty acid proportions than vegetarian diets. Research has shown that these dietary factors can promote subtle but adverse changes in the brain that impair mood state.

Methods: In a pilot randomized controlled trial, we investigated the effect on mood of removing meat and poultry from the diet of healthy adult omnivores for two weeks. Thirty-nine participants were randomly assigned to one of three diet groups: the control group maintained regular intake of flesh foods (CON); the fish group consumed 3-4 servings/wk of seafood but restricted all meat and poultry (FISH), or the vegetarian group restricted all animal protein sources except for dairy (VEG). At baseline and at end of trial, participants completed a validated food frequency questionnaire (FFQ) and two validated psychometric scales, the Profile of Mood States (POMS) and the Depression Anxiety and Stress Scales (DASS).

Results: After 2 weeks, total mean scores for both psychometric tests declined significantly in VEG participants (DASS: -12.2±7.4, p=.011; POMS: -17.9±6.6, p=.015; Wilcoxon Signed Rank Test). Significant reductions in VEG were observed in total fats, dietary eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), arachidonic acid, and protein intake. FISH participants significantly increased their EPA/DHA intakes and decreased their saturated fat intake but mood scores were not significantly reduced.

Conclusion: The complete restriction of flesh foods significantly reduced mood variability in omnivores. To our knowledge, this is the first trial investigating the mood effects of a vegetarian diet.