Orthorexic tendencies moderate the relationship between semi-vegetarianism and depressive symptoms

Purpose: Vegetarianism and semi-vegetarianism (i.e., overly vegetarian diet with rare consumption of meat) have been repeatedly linked with depression. As the nature of this association is unclear, we explored whether orthorexic (i.e., pathologically healthful eating) tendencies and ecological/ethical motives to follow a vegetarian diet may moderate the relationship between (semi-)vegetarian diets and depressive symptoms. Methods: Five-hundred eleven adults (63.4% females; 71.2% omnivores, 19.2% semi-vegetarians, 9.6% vegetarians) completed the Patient Health Questionnaire (PHQ-9) questionnaire—measuring depressive symptoms—and the Düsseldorf Orthorexia Scale (DOS)—measuring orthorexic tendencies. Based on respective questions, participants were categorized as omnivores, semi-vegetarians, and vegetarians (including vegans) and were asked to indicate whether they chose their diet based on ecological/ethical motives. Moderation analyses were carried out with PROCESS. Results: Adjusted for age, sex, and body mass index, there was a statistically significant interaction effect between diet (omnivore vs. semi-vegetarianism vs. vegetarianism) and DOS scores when predicting PHQ depression scores. At low or medium DOS scores, diets did not differ in PHQ depression scores (all ps > 0.05). At high DOS scores, however, semi-vegetarians had higher PHQ depression scores than both omnivores (p = 0.002) and vegetarians (p < 0.001). The interaction between diet and ecological/ethical eating motives when predicting PHQ depression scores was not statistically significant (p = 0.41). Conclusion: Semi-vegetarians with strong orthorexic tendencies show more depressive symptoms than omnivores and vegetarians. The complex nature of the relationship between vegetarianism and depression requires further investigation. Level of evidence: III, case-control analytic studies.