ST. PAUL, Minn., Aug. 6 (UPI) -- French fries, but not mashed, baked or boiled potatoes, were linked Wednesday to type 2 diabetes in a study whose authors say food preparation, as well as the kinds of foods eaten, makes a difference in reducing health risks.

Researchers at Harvard University's T.H. Chan School of Public Health also found that by swapping out French fries with whole grains, a person can reduce the risk for type 2 diabetes by 19%.

The new paper, led by postdoctoral researcher Seyed Mohammad Mousavi and co-authored by prominent Harvard nutrition and epidemiology expert Walter Willett, was published in The British Medical Journal.

After examining data about the diets and diabetes outcomes of more than 205,000 adults enrolled in a trio of major longitudinal U.S. studies spanning more than three decades, they determined that three servings weekly of french fries was associated with a 20% excess risk of developing type 2 diabetes, or T2D.

Conversely, they saw no significant association between consumption of baked, boiled or mashed potatoes and risk of T2D, despite potatoes being "highly stigmatized" and dismissed as generally unhealthy by some in the nutrition world.