BOSTON, MA – A new international study, published in The British Medical Journal (The BMJ) on August 6, 2025, reveals that frequently eating French fries significantly elevates the risk of developing type 2 diabetes. The research, which analyzed data from over 205,000 U.S. medical professionals, found that individuals consuming French fries three or more times per week faced a 20% increased risk of the condition.
This substantial finding highlights that the preparation method of potatoes, rather than the potato itself, is a critical factor in influencing health outcomes.
The Study: Decades of Dietary Data Reveal Clear Link
The comprehensive study, led by Seyed Mohammad Mousavi, a public health expert from Harvard T.H. Chan School of Public Health, tracked the dietary habits and health outcomes of participants over nearly four decades, from 1984 to 2021. Data was drawn from three large-scale U.S. cohort studies: the Nurses’ Health Study, Nurses’ Health Study II, and the Health Professionals Follow-up Study. Throughout this extensive period, over 22,000 new cases of type 2 diabetes were documented among the participants.
Participants regularly completed detailed food questionnaires, providing insights into their consumption of various potato preparations, including French fries, baked, boiled, or mashed potatoes. The researchers then adjusted for lifestyle and other dietary factors related to diabetes risk to isolate the impact of potato consumption.
French Fries vs. Other Potato Preparations: A Stark Difference
A key takeaway from the study is the pronounced difference in risk associated with how potatoes are prepared. While frequent consumption of French fries was linked to a significant increase in type 2 diabetes risk—specifically, a 20% rise for three weekly servings and up to 27% for five or more servings—no such substantial increased risk was found for boiled, baked, or mashed potatoes.
This distinction underscores that potatoes themselves, which contain nutrients like fiber, vitamin C, and potassium, are not inherently unhealthy. It is the deep-frying process and what is often added to French fries that transforms them into a food item with higher health risks.
Why French Fries Pose a Higher Risk
Experts point to several factors that contribute to the elevated risk associated with French fries:
- High Fat and Calorie Content: Deep-frying causes potatoes to absorb large amounts of oil, significantly increasing their calorie and unhealthy fat content.
- Inflammation and Insulin Resistance: French fries are often cooked in oils high in unhealthy fats and sodium, which can contribute to chronic inflammation, weight gain, and insulin resistance—all key factors in the development of type 2 diabetes.
- Ultra-Processed Nature: French fries are frequently classified as ultra-processed foods. They often contain additives, preservatives, emulsifiers, and refined oils, which can negatively impact gut microbiome and promote insulin resistance over time.
- Rapid Blood Sugar Spikes: The high starch content of potatoes, combined with the frying process, can lead to a high glycemic index and load, causing rapid blood sugar spikes.
Dr. Kawther Hashem, a lecturer in public health nutrition at Queen Mary University of London, emphasized, “Potatoes can be part of a healthy diet, but it’s how we prepare them that makes the difference.” Similarly, registered dietitian Nichola Ludlam-Raine noted that “Frying potatoes increases their energy density… and often introduces harmful compounds like trans fats or advanced glycation end products, especially when oils are reused.”
Public Health Implications and Recommendations
The study’s findings reinforce the importance of dietary choices and preparation methods in preventing type 2 diabetes. Seyed Mohammad Mousavi stated, “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.”
The researchers also explored the impact of food substitutions. Replacing three weekly servings of French fries with whole grains, such as whole-grain pasta or bread, was estimated to reduce the risk of type 2 diabetes by as much as 19%. This suggests that even small dietary adjustments can have a significant positive impact on long-term metabolic health.
For policymakers and individuals alike, the message is clear: limiting the consumption of French fries and opting for healthier, whole-grain carbohydrate sources can play a vital role in mitigating the risk of type 2 diabetes across the population. An occasional serving of fries is unlikely to cause harm, but moderation is key, with an emphasis on balanced, whole-food meals for sustained metabolic health.
