Differences in Serum Cytokine Profiles Between Vegetarians and Omnivores: Exploratory Assessment of Dietary Factors

Background/Objectives: Evidence suggests that plant-based diets are associated with reduced risk of chronic inflammatory diseases and lower circulating C-reactive protein (CRP) levels. However, associations with other inflammatory biomarkers, including interleukins (ILs), tumor necrosis factors (TNFs), interferons (IFNs), and chemokines, remain limited and inconclusive. This study compared multiple serum cytokine and chemokine levels between healthy vegetarians and omnivores. Methods: 160 apparently healthy, normal-weight participants aged 25–50 years, without acute and chronic illnesses or allergies, were included: 80 omnivores and 80 vegetarians (67 vegans and 13 lacto-ovo vegetarians). Serum concentrations of 13 cytokines/chemokines were measured using flow cytometry with a LEGENDplex™ bead-based multiplex immunoassay kit. Anthropometry, standard clinical hematological and biochemistry parameters, CRP, and dietary intakes were also analyzed. Results: The groups did not differ by sex (50% women), age, smoking, physical activity, or anthropometrics. Vegetarians had lower levels of TNF-α, IL-6, IL-8, IL-10, IL-12p70, IL-17A, IFN-γ, and IFN-α2, as well as lower leukocyte and lymphocyte counts, with no difference in IL-1β, IL-18, IL-33, IL-23, MCP-1, or CRP. The differences persisted after adjustment for potential confounders (although fewer remained significant after multiple-testing correction), and were principally present in both vegetarian subgroups, alongside substantial differences in multiple dietary factors. Regression analyses further confirmed the association of vegetarian dietary patterns with cytokine levels that differed. Conclusions: Vegetarian dietary patterns were associated with lower circulating concentrations of selected cytokines/chemokines in this cohort. However, the number of associations remaining after multiple-testing correction was limited; there was high multicollinearity between dietary factors, and causality could not be established. Further research is needed to elucidate causal relationships, specific dietary factors, underlying mechanisms, and clinical implications.