High-carb diet linked to breast cancer risk

The new findings also don't mean it is safe or healthful to eat lots of meat, cheese, or fats, as many people who go on low-carb diets do, specialists say.

"There are many concerns with eating diets high in animal fat," said Dr. Walter C. Willett, chief of nutrition at the Harvard School of Public Health. "If people do want to cut back on carbohydrates, it's really important to do it in a way that emphasizes healthy fats, like salads with salad dressings."

Willett worked on the study with doctors at Instituto Nacional de Salud Publica in Cuernavaca, Mexico. It was funded by the US Centers for Disease Control and Prevention, the Ministry of Health of Mexico, and the American Institute for Cancer Research. Results were published today in the journal Cancer Epidemiology, Biomarkers & Prevention.

Fats, fiber, and specific foods have long been studied for their effects on various types of cancer, but few firm links have emerged. Being overweight is known to raise risk, but the new study took that into account and still found greater risk from high carbohydrate consumption.

Scientists think carbs may increase cancer risk by rapidly raising sugar in the blood, which prompts a surge of insulin to be secreted. This causes cells to divide and leads to higher levels of estrogen in the blood, both of which can encourage cancer.

A study earlier this year suggested that high-carb diets modestly raised the risk of colon cancer. Little research has been done on the effect of such diets on breast cancer, and results have been mixed. One study last year found greater risk among young women who ate a lot of sweets, especially sodas and desserts.

For this study, researchers enrolled 475 women newly diagnosed with breast cancer and a comparison group of 1,391 healthy women in Mexico City who were matched for age, weight, childbirth trends, and other factors that affect the odds of getting the disease.

Women filled out a lengthy food questionnaire developed by Willett and widely used in nutrition studies, and were divided into four categories based on how much of their total calories came from carbohydrates.