A big European study has found an association between post-menopausal women’s glycemic load and carbohydrate intake and their likelihood of having a relatively uncommon but often fatal form of breast cancer.

Published in the American Journal of Clinical Nutrition, the analysis of data for 334,849 women ages 34 to 66 from the European Prospective Investigation into Cancer and Nutrition study found no association overall between glycemic load or carbohydrate consumption and breast-cancer risk during the 11.5-year follow-up, during which 11,576 women were found to have breast cancer.

But when researchers looked specifically at post-menopausal women, those with the highest glycemic load were 36 percent more likely to have estrogen-receptor-negative breast cancer than those with the lowest glycemic load (with 158 cases in the highest-GL group versus 11 cases in the lowest-GL group). Similarly, the highest intake of carbohydrates was associated with a 41-percent increased risk of ER-negative breast cancer compared to the lowest carbohydrate intake.

Glycemic load (GL) is a measure of how a carbohydrate-containing food increases a person’s blood-sugar level. A diet with a high glycemic load may stimulate overproduction of insulin, which in turn may promote development of some diseases, including diabetes and cancer. High-GL foods include cakes, cookies and white bread.

ER-negative breast cancers (those in which the cancer cells do not have a receptor to bind to the hormone estrogen) account for about a quarter of breast cancer cases, according to the paper, but they tend to be more lethal than ER-positive breast cancers (those in which the cancer cells can bind to estrogen) because they often grow faster and don’t respond to hormone-based treatments.

The authors note that their study, while offering intriguing insight into the relationship between diet and breast cancer, does not establish that eating high-GL or high-carbohydrate foods directly increases breast cancer risk. It merely observes an association that warrants investigation through further research.