Carbohydrate quality index and breast cancer risk in a Mediterranean cohort: The SUN project

Background & aims: Beyond the quantity of carbohydrate intake, further research is needed on the relevance of carbohydrate quality. Thus, we evaluated the association between an a priori defined carbohydrate quality index (CQI) and the incidence of breast cancer (BC) in a Mediterranean cohort study.

Methods: We used a validated semi-quantitative 136-item food-frequency questionnaire (FFQ) in a prospective follow-up study of 10,812 middle-aged women. We evaluated at baseline the CQI following 4 criteria: dietary fiber intake, glycemic index, whole-grain:total-grain carbohydrates ratio and the solid carbohydrate:total carbohydrate ratio. Subjects were classified into quartiles according to the final CQI score.

Results: During a median follow-up of 11.8 years, we confirmed 101 incident cases of BC. Our study suggests that a higher quality of carbohydrate intake, as measured by the baseline CQI, was associated with a lower risk of BC [HR _{Q4 vs. Q1} 0.39 (95% CI 0.17, 0.87)]. Particularly, a higher whole-grain:total-grain carbohydrates ratio was associated with lower risk of BC [HR _{T3 vs. T1} 0.56 (0.34, 0.90)]. When we stratified by menopausal status, we found an inverse association between CQI and BC in the comparison of extreme quartiles among premenopausal women.

Conclusions: In this Mediterranean cohort, a better quality of dietary carbohydrate intake showed a significant inverse association with the incidence of BC, which suggests that strategies for cancer prevention should highlight the quality of this macronutrient.

Keywords: Breast cancer; Carbohydrate quality; Fiber; Glycemic index; Liquid carbohydrates; Whole grain.