Diets high in refined carbohydrates are suspected of increasing breast cancer risk and recurrence. Diets with a high glycemic load appear to increase the risk of breast cancer even in women who are not overweight. Several studies have reported a higher risk of breast cancer among women who consume a lot of sweets or sweet desserts. It is plausible that high carbohydrate intake could increase breast cancer risk through its influence on blood glucose and insulin levels, sex hormones, and insulin-like growth factor 1 (IGF-1). Now a new study has reported that carbohydrate intake can have a dramatic influence on the risk of recurrence in approximately half of breast cancer survivors.

Insulin-like growth factor signaling and breast cancer

Estradiol (E2) and IGF-1 promote breast cancer together and independently by inhibiting cellular processes designed to repress breast cancer growth. While both estrogen receptor (ER) and IGF-I signaling are known to be important for breast cancer, as well as for normal breast development, interaction between these pathways is not well understood.

Each gene encodes a unique protein that performs a specialized function in cells. Cells use a two-step process of transcription and translation to read the gene and produce its protein. Gene transcription is the process by which genetic information is copied from DNA to RNA. This is followed by translation, in which the RNA is read and a specific protein is produced.

IGF-I was found in one study to regulate the RNA of five to ten times as many genes as E2. Many genes were co-regulated by both. The expression of a number of potential tumor suppressors was inhibited by IGF-I and E2. Expression of co-regulated genes correlated with poor breast cancer prognosis. The study results also suggested downstream convergence of the two pathways.

Latest research finds carbohydrate intake can greatly influence recurrence

The nested case-control study referenced at the beginning of this news article was designed to investigate how the IGF-1 receptor, in combination with diet, may influence breast cancer recurrence. The study included 265 postmenopausal breast cancer survivors. Breast cancer tissue (obtained from each participant's primary tumor) was stained to determine IGF-1 receptor status. Half of tumors were found to be IGF-1 receptor positive. Twenty-four hour dietary recalls were used to assess the change in carbohydrate intake from enrollment to one year later.

A total of 91 of the study participants eventually developed a breast cancer recurrence. These cases were matched to the remaining 174 participants who acted as controls. Increased risk of recurrence was associated with IGF-1 receptor positive status and, separately, with a stable or increased intake of carbohydrates. There was a slight but significant interaction between those two variables. Carbohydrate intake had no measurable impact on the risk of recurrence among women who were IGF-1 receptor negative. However, for the 50% of women whose breast cancer was IGF-1 receptor positive, carbohydrate intake that was constant or increased after diagnosis resulted in more than five times the risk of recurrence compared to a reduction in carbohydrate intake. The authors conclude that, among women whose tumor tissue is positive for the IGF 1 receptor, reducing carbohydrate intake after diagnosis could reduce the risk of recurrence. The findings need replication in a larger sample, according to the authors.

Please see our article on glycemic load for more information.