• Posted August 7, 2025

French Fries Linked to Higher Odds for Type 2 Diabetes

The next time you’re asked "Fries with that?," maybe say no: Regular consumption of the potato-based treat raises your odds of type 2 diabetes by 20%, new research shows. 

On the other hand, swapping out those fries for whole-grain foods could lower your odds for the blood sugar disease by 19%, the same study found.

“The public health message here is simple and powerful: Small changes in our daily diet can have an important impact on risk of type 2 diabetes. 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,” said study co-author Dr. Walter Willett, professor of epidemiology and nutrition at Harvard University.

His team published its findings Aug. 6 in The BMJ. 

As Willett’s team explained, prior research had shown the lowly potato to be a major dietary culprit in fostering diabetes.  

But does the way in which potatoes are cooked matter?

“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?” lead author Seyed Mohammad Mousavi said in a news release. Mousavi is a postdoctoral research fellow in Harvard’s Department of Nutrition.

The new study focused on data involving more than 205,000 people enrolled in the Nurses’ Health Study, the Nurses’ Health Study II, and the Health Professionals Follow-up Study.  

These studies are a goldmine for nutrition researchers, because for three decades participants filled out detailed dietary questionnaires.  

Included in those surveys were questions about how many times per week they ate French fries; baked, boiled or mashed potatoes; and whole grains.

Of course, each participant’s health was also tracked for more than 30 years. Over that time, 22,299 participants developed type 2 diabetes, the most common form of the disease.

When it came to potatoes, how they were cooked did matter: While just three servings per week of French fries hiked diabetes risk by 20%, eating potatoes baked, boiled or mashed had no influence on diabetes risk. 

And replacing those three French fry orders with whole grains — for example, whole grain pastas or bread — cut the odds of type 2 diabetes by up to 19%, the Harvard team found. Even subbing refined (not whole) grains for French fries helped lower diabetes risk. 

These findings were backed up by two separate analyses, in which data from a number of prior studies involving more than 500,000 people (including 43,000 cases of type 2 diabetes) yielded similar results when it came to French fries versus whole grains.

“For policymakers, our findings highlight the need to move beyond broad food categories and pay closer attention to how foods are prepared and what they’re replacing," Willett said in a Harvard news release. "Not all carbs — or even all potatoes — are created equal, and that distinction is crucial when it comes to shaping effective dietary guidelines.”

The study was funded by a grant from the U.S. National Institutes of Health. 

More information

Find out more about type 2 diabetes at the U.S. Centers for Disease Control and Prevention.

SOURCE: Harvard T.H. Chan School of Public Health, news release, Aug. 6, 2025