Carbohydrates have been taking a beating for their putative effect on the waistline in recent years. Now they're coming under fire for potentially putting women at an increased risk of breast cancer.

A study of 1,866 Mexican women has found that those who obtained more than 62 percent of their calories from carbs were more than twice as likely to develop breast cancer compared to women whose carb intake accounted for 52 percent or less of their diet. (The investigators accounted for body mass index and other potentially confounding factors.) "Scientists have long suspected that diet was among the factors contributing to breast cancer," says study co-author Walter Willet of Harvard University. "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."

The new work found a particularly strong link between consumption of sweets and elevated breast cancer risk, whereas ingestion of insoluble fiber was associated with lower risk. In explanation, the researchers note that eating carbs triggers a cascade of events leading to increased secretion of insulin and another protein that can boost cell proliferation and thus lead to cancer. Fiber, on the other hand, may mitigate the effects of carbs by interfering with their absorption.

"This study raises important questions about high carbohydrate diets, particularly among populations or individuals prone to insulin resistance," Willet remarks. "However, one study is not enough to make major changes in diet, and more work on this topic is urgently needed." A report detailing the findings appears in the current issue of the journal Cancer Epidemiology Biomarkers and Prevention.

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