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

OBJECTIVES: Beyond the quantity of carbohydrate intake, further research is needed on the relevance of carbohydrate quality and chronic conditions. No previous longitudinal study has assessed the association between an integrated multi-dimensional index for carbohydrate intake quality and the risk of breast cancer (BC). Thus, we evaluated the association between an a priori defined carbohydrate quality index (CQI) and the incidence of BC in a Mediterranean cohort study. METHODS: We used a validated semi-quantitative 136-item food-frequency questionnaire (FFQ) to evaluate the CQI at baseline, as previously described (PMID: 31,868,210), based on 4 criteria: dietary fiber intake, glycemic index, whole grain/total grain ratio, and solid carbohydrate/total carbohydrate ratio), in 10,812 middle-aged women. RESULTS: During a median follow-up of 11.8 years, we confirmed 101 incident cases of BC. A higher CQI (fourth quartile) was associated with a lower risk of BC [HR (Q4 vs. Q1) 0.39 (95% CI 0.17, 0.87) p for trend: 0.049]. When we additionally included probable incident cases (n = 190) this association between CQI and BC persisted with a relative risk reduction of 48% for the overall sample of women [HR (Q4 vs. Q1) 0.52, 95% CI 0.31, 0.89; p for trend: 0.034]. Furthermore, when we stratified by menopausal status, we found a significant inverse association between the CQI and premenopausal BC for both confirmed (HR (T3 vs. T1) 0.32, 95% CI 0.10, 1.00) and probable (HR (T3 vs. T1) 0.46, 95% CI 0.22, 0.96) cases. CONCLUSIONS: In this Mediterranean cohort, a better quality of dietary carbohydrate intake showed a significant inverse association with the incidence of BC, particularly among premenopausal women, which suggests that strategies for cancer prevention should focus, in relation to diet, on the quality of this macronutrient. FUNDING SOURCES: The SUN Project has been supported by the Institute of Health Carlos III, the European Regional Development Fund, the Navarra Regional Government, and the University of Navarra.