Background Diet is known as one of the major modifiable risk factors for the regulation of chronic inflammation. Epidemiologic studies that have examined the association between dietary inflammatory potential and breast cancer risk have been inconsistent. The aim of this study was to assess the association between the Adapted Dietary Inflammatory Index (ADII) and breast cancer risk.

Methods The study was conducted using data from the CECILE study, a population-based case-control study in 2 French departments (Ille-et-Vilaine and Côte d’Or). The group of cases included women aged 25–75 years with a cancer of the breast diagnosed between 2005 and 2007. Controls were selected at random from the telephone directories and were frequency-matched to the cases by age and department.

Information on socio-demographic characteristics, lifestyle-related factors, hormonal and reproductive history, previous medical conditions, and family history of breast cancer were obtained from a structured questionnaire during in-person interviews. Information on dietary habits the year prior to inclusion was self-reported by the study subjects using a 150-items food frequency questionnaire.

The ADII for each subject was calculated as the sum of the standardized energy-adjusted intake of each dietary component weighted by its dietary inflammatory score, as described by (van-Woudenbergh et al, Am J Clin Nutr, 2013).

Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated from multivariable logistic regression after controlling for potential confounders selected among breast cancer risk factors.

Results The analysis was based on 840 cases and 908 controls who completed the food frequency questionnaire. The OR for breast cancer in women in the highest quartile of ADII as compared to women in the lowest quartile, was 1.43 (95% CI: 1.07–1.90) and there was a significant trend of increasing risk with increasing ADII. The corresponding OR in menopausal women was 1.58, 95% CI: 1.08–2.31, while no statistically significant association was observed in premenopausal women

Conclusion Our results suggest that a pro-inflammatory diet increases the risk of developing breast cancer among post-menopausal women.