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Background: Hashimoto's thyroiditis (HT) is an inflammatory disease characterized by increased reactive oxygen species. Diets rich in anti-inflammatory and antioxidant properties may be linked to a reduced risk of developing HT. The aim of this study was to investigate the association between the dietary inflammatory index (DII) and dietary total antioxidant capacity (DTAC) with HT in Iranian adults., Methods: The study was a hospital-based case-control study conducted on 230 participants (115 cases and 115 controls). Dietary intake was assessed using a food frequency questionnaire (FFQ). The FFQ data were used to calculate DII and DTAC scores. Anthropometric measurements, thyroid function, and antibody tests were evaluated using standard methods. Multivariable logistic regression analysis was performed in both raw and adjusted models to determine the association between DII and DTAC scores with HT., Results: The average age of the participants was 39.76 ± 9.52 years. The mean body mass index in the case and control groups was 28.03 ± 6.32 and 26.43 ± 5.13 (kg/m 2 ), respectively (P = 0.036). In the HT group, the DII level was higher (P < 0.001) and the DTAC level was lower than those in the healthy group (P = 0.047). In the multivariable logistic regression model, after adjusting for confounding factors, subjects in the last tertile of DII had a nonsignificantly higher HT risk than those in the first tertile (OR = 1.75; 95% CI = 0.83-3.65; P = 0.130). Regarding DTAC, the subjects in the last tertile of DTAC had a significantly decreased risk of HT (OR = 0.47; 95% CI = 0.23-0.98; P = 0.043) compared to those in the first tertile. The DII had a positive correlation with anti-thyroid peroxidase antibody (anti-TPO), thyroglobulin antibodies (TG-Ab) and thyroid-stimulating hormone, while DTAC had a negative correlation with anti-TPO and TG-Ab (P < 0.050)., Conclusion: The increase in DII is not associated with an increase in the risk of HT, while DTAC can significantly reduce its risk. Having an anti-inflammatory and antioxidative diet can be effective in improving thyroid function. These conclusions should be confirmed in additional prospective studies., (© 2024. The Author(s).)