A high-carbohydrate diet loaded with starches such as potatoes may boost the risk that breast cancer returns, new research finds.

“Women who increased their carbohydrates and particularly their starch intake had a greater risk of recurrence than the women who decreased [it],” said researcher Jennifer Emond, a public health doctoral student at the University of California, San Diego.

Carbohydrates provide nutrients and energy, but some carbs are better than others. Refined carbs – such as those found in white bread -- contain more starch. One slice of bread has 12.5 grams of carbs (10 grams of which are starch) and one cup of pasta has 43 grams of carbs (36 are starch), according to the U.S. Department of Agriculture.

Researchers tracked 2,650 breast cancer survivors for recurrence, after examining what they ate over a one-year period. At the beginning of the study, carb intake was about 233 grams per day. Women whose cancer returned had increased their carbs by 2.3 grams per day, on average. The cancer did not return in women who had decreased their daily carb intake by an average of 2.7 grams.

It is unclear why starch is linked to breast cancer recurrence. Starch boosts a person’s insulin levels, which levels have been linked to an increased risk of breast cancer, Emond noted. The increased amount of insulin in the body may aid tumor growth, she theorized.