High glycemic diet and breast cancer occurrence in the Italian EPIC cohort

There are theoretical reasons for suspecting that a high glycemic index (GI) or glycemic load (GL) diet may increase breast cancer risk, perhaps via an effect on the insulin-like growth factor (IGF) axis. However observational studies have produced inconsistent findings and it is controversial whether breast cancer risk is influenced by the carbohydrate characteristics of the diet. We prospectively investigated the association between dietary GI and GL and breast cancer in the Italian section of the European Prospective Investigation into Cancer and Nutrition (EPIC).

Women were recruited from 1993 to 1998 at five centers: Varese and Turin (north Italy), Florence (central Italy), and Ragusa and Naples (south Italy). Participants completed validated food frequency questionnaires from which GI and GL were estimated. Multivariable Cox proportional hazard regression models quantified the association between breast cancer risk and total carbohydrate intake, GI, and GL. During 11 years of follow-up, 879 breast cancer (797 invasive and 82 in situ) cases were indentified. High dietary GL was associated with increased breast cancer risk (RR 1.45, 95% CI = 1.06-1.99; highest vs. lowest quintile; p-trend 0.029), whereas dietary GI and total carbohydrate had no influence. The association was not modified by menopausal status or body mass index.

Our data indicate that, in a Mediterranean population characterized by traditionally high and varied carbohydrate intake, a diet high in GL plays a role in the development of breast cancer.