Breast cancer is one of the most common cancers among women. There is no study on the association of food-based dietary inflammatory index (FDII) and the odds of breast cancer. This study was conducted to investigate the association between FDII and the odds of breast cancer in Iranian women.

Methods: In this population-based case-control study, dietary intakes of 350 pathologically confirmed new cases of breast cancer and 700 controls were collected by completing a 106-item semi-quantitative food frequency questionnaire (FFQ). The FDII score was calculated based on participants’ dietary intakes. Data on potential confounding variables were also collected using a pre-tested questionnaire.

Findings: The mean FDII score ranged from -34.01 to 4.19. A significant positive association was found between FDII and the odds of breast cancer, such that after taking potential confounders into account, women in the highest tertile of FDII score were 1.52 times more likely to have breast cancer compared with those in the lowest tertile [odds ratio (OR): 1.52, 95% confidence interval (CI): 1.05-2.18]. Such a significant positive association was also observed among postmenopausal women, either before (OR: 1.53, 95% CI: 1.09-2.14) or after (OR: 1.54, 95% CI: 1.05-2.27) controlling for confounding variables. The same association was also seen in normal-weight women, and it remained significant even after controlling for potential confounders (OR: 1.58, 95% CI: 1.04-2.41).

Conclusion: We found a significant positive association between FDII and the odds of breast cancer in women, particularly postmenopausal ones. Prospective studies are needed to examine this relationship further.