Inflammatory Potential of Diet and Breast Cancer Risk: A Population‐Based Case–Control Study

ABSTRACT Chronic inflammation may contribute to breast cancer (BC). The Dietary Inflammatory Index (DII) and energy‐adjusted DII (E‐DII) quantify the inflammatory potential of diet. This case–control study evaluated associations of the DII and E‐DII with BC risk among Iranian women. We recruited 600 newly diagnosed BC cases and 600 population‐based controls from Isfahan, Iran. Dietary intake was assessed using a validated 168‐item food frequency questionnaire (FFQ). DII and E‐DII scores were calculated based on 26 and 25 food parameters, respectively. Logistic regression models were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Multivariable‐adjusted models accounted for confounders including age, body mass index, reproductive history, and sunlight exposure. Higher E‐DII scores were significantly associated with an increased odds of developing BC. In the fully adjusted models, women in the highest quartile of the E‐DII had 63% greater risk than those in the lowest quartile (adjusted OR: 1.63; 95% CI: 1.08–2.45). Analyses based on continuous E‐DII also showed that each unit increase in the E‐DII score was linked to a 14% increase in BC odds (adjusted OR: 1.14; 95% CI: 1.05–1.24). In contrast, DII scores were not significantly associated with BC risk in any of the models. This study demonstrated that diets with stronger inflammatory properties, indicated by elevated E‐DII scores, are associated with a higher risk of BC among Iranian women. These outcomes underline the value of using energy‐normalized inflammatory indices when assessing dietary influences on cancer risk.