People with Type 2 diabetes on a high-fiber diet kept their blood sugar under better control when they ate foods like beans and nuts instead of the recommended whole-grain diet, researchers have found.

Beans and nuts are among foods that only modestly increase blood glucose levels; scientists describe these foods as having a low glycemic index. The new study, which lasted six months, is one of the largest and longest to assess the impact of foods with a low-glycemic index, researchers said.

Participants on the low-glycemic diet also saw significant improvements in cholesterol after six months, with increases in HDL, the so-called “good” cholesterol associated with a reduced risk of heart disease, the study found.

“That’s an important issue today, because there’s a double whammy for people who are diabetic," said Dr. David J. A. Jenkins, lead author of the report and a professor of nutritional sciences at the University of Toronto. "If they’re men, they have twice the risk of heart disease, and if they’re women, they have four times the risk. If you can hit the heart disease to which they’re particularly vulnerable, you may have something useful."