Dieters cutting down on carbohydrates may be lowering their risk of breast cancer while they're shedding pounds, according to a study appearing in the journal Cancer Epidemiology, Biomarkers & Prevention. In a study of women in Mexico, those who derived 57 or more percent of their total energy intake from carbohydrates incurred a risk of breast cancer 2.2 times higher than women with more balanced diets. Dietary patterns in Mexico are characterized by higher consumption of carbohydrates and lower intake of fat and animal protein. The team of researchers, from the Instituto de Salud Pública in Mexico and the Harvard School of Public Health, suggest that the association between carbohydrates and breast cancer may be related to elevated levels of insulin and insulin-like growth factor binding proteins in the blood.
"Scientists have long suspected that diet was among the factors contributing to breast cancer," said study co-author Walter Willett. "Now, with studies like ours, we are beginning gradually to understand what elements of diet specifically are associated with the disease, and to grasp the chemical and biological processes that contribute to it at the cellular level."
Of all the carbohydrate compounds, sucrose and fructose demonstrated the strongest association with breast cancer risk in the study. Sucrose is derived from sugar cane, sorghum and the sugar beet; it is most commonly found in table sugar and sweetened prepared foods and beverages. Fructose is a component of sucrose and is also found in fruit. Eating sweets and starches causes a rapid rise in the body's blood sugar levels, which in turn cues the production of insulin and triggers a biological process that ultimately can influence carcinogenesis by causing cells to proliferate.
Insulin and an insulin-like growth factor also may contribute to higher circulating levels of biologically active estrogens, a risk factor for breast cancer in pre-menopausal women. Ninety percent of breast tumors are insulin-receptor positive and over-express the insulin-like growth factor.
Dietary fat - a contributor to obesity - fared well in the research, showing no significant association with breast cancer risk overall. Willett noted, however, that the intake of polyunsaturated fat by the women in the study group was only about half that of the U.S. population. Insoluble fiber intake was associated with lower risk of breast cancer, possibly because fiber may modulate the absorption of carbohydrates and thus affect the glycemic response.
"This study raises important questions about high carbohydrate diets, particularly among populations or individuals prone to insulin resistance. However, one study is not enough to make major changes in diet, and more work on this topic is urgently needed," Willett said.
