NEW YORK: A new study by Harvard University researchers has found that eating French fries significantly increases the risk of type 2 diabetes, whereas boiled, baked, or mashed potatoes do not carry the same risk.
The study published in the British Medical Journal was led by Dr. Seyed Mohammad Mousavi, while renowned nutritionist Dr. Walter Willett is also among the co-authors.
According to the researchers, while previous studies hinted at a link between potatoes and T2D, the evidence was inconsistent and often lacked detail on cooking methods and the potential effects of substituting other foods for potatoes.
“Our study offers deeper, more comprehensive insights by looking at different types of potatoes, tracking diet over decades, and exploring the effects of swapping potatoes for other foods,” said lead author Seyed Mohammad Mousavi, postdoctoral research fellow in the Department of Nutrition.
“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?”
Harvard University researchers analysed data from 205,107 men and women enrolled in the Nurses’ Health Study, Nurses’ Health Study II, and the Health Professionals Follow-up Study. Over a span of more than 30 years, participants regularly completed dietary questionnaires, reporting how often they consumed specific foods—such as French fries, various forms of potatoes, and whole grains.
They also shared new health diagnoses, including type 2 diabetes (T2D), as well as lifestyle and demographic details, which researchers adjusted for in their analysis.
During the study period, 22,299 participants developed T2D.
The findings revealed that consuming French fries three times per week increased the risk of developing T2D by 20%. In contrast, baked, boiled, or mashed potatoes were not significantly linked to an increased risk.
However, the researchers found that substituting whole grains—like whole grain pasta, bread, or farro—for baked, boiled, or mashed potatoes could reduce T2D risk by 4%. Replacing French fries with whole grains could lower the risk by 19%, while even swapping refined grains for French fries showed a protective effect.
“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. 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 corresponding author Walter Willett, professor of epidemiology and nutrition.
“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. Not all carbs—or even all potatoes—are created equal, and that distinction is crucial when it comes to shaping effective dietary guidelines,” he said.
