Eating foods with a high glycemic index (GI) can make your blood sugar rise higher and faster after eating. Theoretically, that could cause unhealthy levels of hormones like insulin, which seem to promote development of some cancers, including breast.
However, research suggests that glycemic index by itself has little to no relation to breast cancer risk.
An analysis of 19 studies found no link between breast cancer risk and diets high in GI beyond what could occur by chance. Even glycemic load (GL), which takes portion size of foods into account, showed no significant link to breast cancer risk. The links were not consistent and could reflect other qualities of those diets. Another analysis that included only studies with a stronger design that follows people over time (called prospective cohort studies) found a weak five to six percent increase in breast cancer risk when comparing diets at the very highest to the very lowest glycemic index or glycemic load, respectively. Read more… “Do foods high in glycemic index increase breast cancer risk?”