Background: Evidence is accumulating that high dietary glycemic index (GI) and glycemic load (GL) are risk factors for several metabolic disorders, e.g. diabetes or cardiovascular diseases, but evidence on GI/GL and cancer is less consistent. However, mechanistic data suggest that food with high-GI may contribute to carcinogenesis through the insulin resistance pathway.Objective: The objective was to study the associations between dietary GI/GL and breast cancer risk.Design: Population based prospective cohort study.Setting and Participants: 81,526 women aged ≥18y (mean age: 40.8±14.0y), free of cancer at baseline and with no prevalence or incidence of diabetes, from the French NutriNet-Santé cohort (2009-2019) were included in the analyses. 24-hour dietary records linked with a nutritional composition table for >3,500 food/beverage items containing GI values and carbohydrate content enabled us to compute average dietary GI and GL.Main outcome measures: Associations between GI; GL; proportion of energy and proportion of carbohydrates from low-GI (GI≤55) and from medium/high-GI (GI>55) foods and risk of breast cancer were assessed by Cox proportional hazard models adjusted for known risk factors (sociodemographic, anthropometric, lifestyle, medical history, and nutritional factors).Results: A higher dietary GL was associated with higer postmenopausal breast cancer risk (n=572, hazard ratio for quintile 5 versus quintile 1: 1.64 confidence interval 1.06-2.55 Ptrend=0.03). Percentage of energy intake from medium/high-GI foods was associated with higher breast cancer risk (HRQ5vs.Q1=1.34 (1.05-1.71), Ptrend=0.04), more specifically postmenopausal breast cancer (HRQ5vs.Q1=1.36 (1.00-1.84), Ptrend=0.02). Carbohydrates intake from medium/high-GI foods was also associated with higher breast cancer risk (HRQ5vs.Q1=1.34 (1.05-1.71), Ptrend=0.04) in both premenopausal (HRQ5vs.Q1=1.49 (1.03-2.17), Ptrend=0.04) and postmenopausal (HRQ5vs.Q1=1.44 (1.08-1.93), Ptrend=0.03) women, whereas carbohydrates from low-GI foods was associated with lower breast cancer risk (HRQ5vs.Q1=0.74 (0.59-0.92), Ptrend=0.04), only among postmenopausal women (HRQ5vs.Q1=0.69 (0.52-0.92), Ptrend=0.03).

Conclusion: The consumption of foods with high-GI was associated increased breast cancer risk. If these results are confirmed dietary GI and GL should be considered as modifiable risk factor for primary breast cancer prevention.

Citation Format: Charlotte Debras, Eloi Chazelas, Bernard Srour, Chantal Julia, Emmanuelle Kesse-Guyot, Laurent Zelek, Cédric Agaësse, Nathalie Druesne-Pecollo, Pilar Galan, Serge Hercberg, Paule Latino-Martel, Mélanie Deschasaux, Mathilde Touvier. Glycemic index, glycemic load and breast cancer risk: Results from the prospective NutriNet-Santé cohort [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr GS2-07.