Researchers at the Karolinska Institute in Stockholm have reported that the “glycemic load” of a woman’s diet may be significantly linked to her risk of developing breast cancer. The findings, reported in the International Journal of Cancer’s July 2009 issue, add even more weight to the idea that a low–glycemic diet is beneficial in a number of different ways.

The glycemic load is a method of ranking foods based on their glycemic index and the kind of “spike” they give to blood sugar and as a result, insulin levels. The glycemic index reflects the speed at which blood sugar rises after a certain food is consumed. Low–glycemic foods like vegetables, nuts, and grains cause it to rise slowly, while high–glycemic foods like baked potatoes, rice, and white bread lead to a faster spike in blood sugar.

Susanna C. Larsson and her team looked at data from over 61,000 women, who had taken surveys that focused on the foods they consumed and their frequency of consumption. In the next 17 years, about 1,900 − or just under 5% − of the women developed breast cancer. The researchers discovered that “glycemic load, but not carbohydrate intake or glycemic index, was significantly positively associated with risk of overall breast cancer.”

However, glycemic load, glycemic index, and carbohydrate intake were all significantly correlated with a particular type of breast cancer: estrogen receptor (ER)–positive/progesterone receptor (PR)–negative breast cancer. Women with the highest glycemic load were at an 81% increased risk of developing ER+/PR– cancer. Those who ate the highest “glycemic index diet” had a 44% higher chance of developing the cancer than those with the lowest glycemic–index diet. And women who had the highest overall carbohydrate intake were at a 34% greater risk of ER+/PR– tumors.

The team did not find a similar connection in the other varieties of cancer they studied (ER+/PR+ and ER–/PR– tumors), which they say is puzzling.

The researchers point out that in contrast to previous research, which has provided mixed results, their findings lend good support for the link between glycemic index, glycemic load, and carbohydrate intake and the risk for developing this particular variety of breast cancer. They suggest that high–glycemic diets may lead to increases in circulating insulin and sex hormone levels, which can aid in the production of estrogen–dependent breast cancer. More research will be needed to determine the exact mechanism behind this connection.