There’s some mixed news for potato lovers.

A new Harvard study has found a connection between potato consumption and a higher risk of developing diabetes. But not all potatoes are created equal — some varieties and preparations are safer than others.

French Fries and Diabetes Risk

Lead author Seyed Mohammad Mousavi, a postdoctoral research fellow in Harvard’s Department of Nutrition, explained the shift in focus: “We’re shifting the conversation from, ‘Are potatoes good or bad?’ to a more nuanced — and useful — question: How are they prepared, and what might we eat instead?”

The study followed more than 205,000 people for over 30 years, tracking their eating habits. Results showed that consuming three servings of French fries each week increased the risk of diabetes by 20 percent. Other types of potatoes, such as baked or mashed, didn’t carry the same risk.

Healthy Swaps Can Lower Risk

Researchers also discovered that substituting potatoes with whole grains reduced type 2 diabetes risk by 4 percent. Swapping fries for whole grains offered even greater protection, lowering risk by 19 percent. Even replacing fries with refined grains like white bread showed some benefit.

“The public health message here is simple and powerful: Small changes in our daily diet can have an important impact on the risk of type 2 diabetes,” said corresponding author Walter Willett, professor of epidemiology and nutrition. “Limiting potatoes — especially limiting French fries — and choosing healthy, whole-grain sources of carbohydrate could help lower the risk of type 2 diabetes across the population.”