The amount of carbohydrates a woman eats, as well as the overall “glycemic load” of her diet, impact her chances of developing breast cancer, Swedish researchers report.

The concept of glycemic load is based on the fact that different carbohydrates have different effects on blood sugar. White bread and potatoes, for example, have a high glycemic index, which means they tend to cause a rapid surge in blood sugar. Other carbs, such as high-fiber cereals or beans, create a more gradual change and are considered to have a low glycemic index.

Dr. Susanna C. Larsson of Karolinska Institute in Stockholm and colleagues analyzed data on 61,433 women who completed “food frequency” questionnaires in the late 1980s.

Over the course of about 17 years, 2952 women developed breast cancer and, according to the investigators, glycemic load “was significantly positively associated with risk of overall breast cancer.” Women with higher glycemic load diets were more apt to develop breast cancer.

In addition, carbohydrate intake, glycemic index and glycemic load were all positively associated with risk of a certain type of breast tumor - namely, estrogen receptor (ER)-positive/progesterone receptor (PR)-negative breast cancer.

Women with the highest “glycemic index diet” had a 44% increased risk of developing ER+/PR- breast cancer compared to women with the lowest glycemic index diet.

Women in the highest category of “glycemic load” had an 81% increased risk of ER+/PR- tumors, and those with the highest carbohydrate intake had a 34% increased risk, compared to those in the lowest groups.

The investigators speculate that high-glycemic load diets may boost breast cancer risk by increasing concentrations of insulin and sex hormones in the body, which may contribute to the development and spread of breast cancer cells.

The findings support the benefits on breast health of a diet high in healthy “low glycemic index” foods.

SOURCE: International Journal of Cancer, July 2009.