Association between the novel dietary index for gut microbiota, biomarkers of hashimoto's thyroiditis and metabolic parameters among women of reproductive age.

BACKGROUND: Emerging evidence highlights the role of gut microbiota in autoimmune diseases, including Hashimoto's thyroiditis (HT). Diet is a key modulator of gut microbial composition. This study investigated the association between a novel Dietary Index for Gut Microbiota (DIGM) and thyroid-related biomarkers among women with HT. METHODS: In this cross-sectional study, 162 women with clinically confirmed HT were enrolled. Dietary intake was assessed using a validated food frequency questionnaire. The DIGM score was constructed based on intake of foods known to influence gut microbial health, with higher scores indicating greater adherence to a microbiota-supportive diet. Anthropometric parameters and serum levels of thyroid hormones, thyroid autoantibodies, lipid profile, and oxidative stress markers were measured. Participants were categorized into tertiles based on DIGM score, and comparisons across groups were made using ANOVA and general linear models, adjusting for potential confounders. RESULTS: Participants in the highest DIGM tertile had significantly lower serum anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-Tg) antibody levels (P < 0.05), lower triglyceride concentrations (p = 0.017), and reduced waist-to-hip ratio (p = 0.030) compared to those in the lowest tertile. No significant differences were observed in TSH, T3, T4, anti-Tg, TAC, or MDA levels across DIGM categories. CONCLUSION: Higher adherence to a microbiota-supportive dietary pattern, as reflected by the DIGM score, was associated with favorable immune and metabolic profiles in women with HT. Due to the cross-sectional design of the study, causal relationships cannot be inferred. Further longitudinal or intervention studies are needed to elucidate causality and to suggest dietary modulation of gut microbiota as a non-pharmacological approach to support management of autoimmune thyroid disease. CLINICAL TRIAL NUMBER: Not applicable.