Beyond Dietary Identity: Habitual Food Consumption, Lifestyle Characteristics, and Mental Health in Adults Following Plant-Based Diets

Background/Objectives: Evidence linking plant-based diets with mental health is mixed. One reason may be that dietary labels do not always reflect habitual food intake and often coincide with other lifestyle characteristics. Methods: We conducted a cross-sectional secondary analysis of 158 Polish adults: 105 omnivores and 53 participants who identified as following plant-based diets (34 vegetarians and 19 vegans). Habitual intake frequencies for 33 food groups and diet-quality indices were derived from KomPAN. Anxiety and depressive symptoms were assessed with HADS-M, empathy with the EQ-Short/SSIE, and physical activity with IPAQ. Self-identified dietary pattern was the primary exposure; meat/fish-abstention definitions were examined in sensitivity analyses. Results: Compared with omnivores, plant-based participants had lower BMI and nHDI scores, higher DQI values, and, among those with valid IPAQ data, higher physical activity. Nineteen of 33 food groups differed after false-discovery-rate correction. We found no statistically significant association between dietary identity and HADS-A or HADS-D in crude, minimally adjusted, or broader sensitivity models; the confidence intervals, however, were too wide to establish equivalence or rule out an association. Of the 53 self-identified plant-based participants, 36 (67.9%) met the meat/fish-abstention criterion and 17 (32.1%) did not. IPAQ analyses included 120 participants, and inverse-probability-weighted sensitivity analyses produced similar HADS estimates. No individual food-frequency variable was associated with HADS-A or HADS-D after multiplicity correction. In exploratory analyses, more frequent vegetable consumption was positively associated with empathy. Conclusions: Dietary identity corresponded to clear differences in habitual food consumption, diet quality, and selected lifestyle characteristics, but we did not detect a statistically significant association with anxiety or depressive symptoms. The observed mismatch between dietary identity and reported behavior highlights the value of measuring both in studies of plant-based diets and psychological outcomes.