New research suggests that overeating, especially easily absorbed carbs like white bread, white rice, white pasta, potatoes and sweets, may change the body’s delicate hormone balance, creating an environment conducive to cancer growth. So writes Michael Pollak, M.D., McGill University oncology professor director of the Cancer Prevention Center at the Jewish General Hospital in Montreal, in Cancer Prevention Research.

Maintaining a healthy weight, watching calories and choosing whole grains and veggies over white flour and sugar may do more than reduce your risk of diabetes and heart disease, it turns out. It may also cut your risk of breast cancer, and other cancers, too.

The newest piece in the cancer-carb puzzle is the role of insulin, the hormone that helps our bodies use or store glucose from carbs. Eating easily absorbed carbs causes a rapid spike in blood sugar that requires a high insulin response; plus, obesity is linked with an alarming rise in insulin levels among the general population, says Dr. Pollak, and high-calorie/high-carb diets along with increasing weight may contribute to rising insulin levels. “Insulin and insulin-like growth factors go up when you eat too much, and many, though not all cancers, grow more successfully with high levels of these hormones," Dr. Pollak says. "There are many people whose insulin levels are higher than optimum, even though they do not have diabetes. These people are at increased risk of cancer, and if they do get cancer, they have a worse outcome. We think that’s because their high insulin is stimulating the growth of the cancer cells.”

A New Way to Treat Cancer?

This new research may change cancer treatment methods, especially in people with diabetes, and may even lead to new medical prevention approaches. In a July study of women with both diabetes and breast cancer, those who took metformin, a drug that helps control insulin levels, were three times more likely to go into remission than those who didn’t take the medication. They also were more likely to go into remission than breast cancer patients who didn’t have diabetes. While this was a small study, “these results are pretty impressive,” says Ana M. Gonzalez-Angulo, M.D., of the University of Texas MD Anderson Cancer Center in Houston, and the lead author of the study. Other studies have shown that people with diabetes who take metformin develop fewer cancers in general. Next step: Research on whether metformin’s anti-cancer action also works in healthy people who simply want to reduce their risk of cancer.

For now, though, the new research doubles down on the incentive to watch your weight, exercise, control calories and choose “good” carbs, like whole grains, beans, fruits and vegetables.

“Don't be misled by fad diets that make blanket pronouncements on the dangers of carbohydrates,” says the Harvard School of Public Health. “They are an important part of a healthy diet.” It’s a matter of “good carbs, not no carbs.” So stick to complex carbs like as much as possible. For more on choosing “smart carbs” see Dr. Madelyn Fernstrom’s blog post on “5 Ways to Be Carb-Smart.”

Dr. Gonzalez-Angulo's advice? “Lose weight, eat a balanced diet and exercise," she says. "That’s the lecture I give all my patients!”

Dr. Madelyn Fernstrom on Carbs

Related Links:
Dr. Nancy Snyderman: How Many Carbs Do You Really Need?
Ask Dr. Madelyn Fernstrom: Prediabetes—What To Eat? 
Dr. Madelyn Fernstrom: Eat Less, Live Longer?
Olive Oil & Veggies: Mediterranean Secret to Long Life?