Three Servings of French Fries a Week Tied to a 20% Higher Diabetes Risk, 40-Year Study Finds

It turns out the humble potato may not be the villain in the diabetes story — the deep fryer is. A sweeping new study that followed more than 205,000 people for nearly four decades found that eating French fries three times a week was associated with a 20% higher risk of developing type 2 diabetes, while baked, boiled and mashed potatoes carried no added risk at all.

The research drew on data from more than 205,000 U.S. health professionals enrolled in three large long-term studies conducted between 1984 and 2021. None of the participants had diabetes, heart disease or cancer when the tracking began. Over the decades of follow-up, 22,299 of them developed type 2 diabetes, giving researchers an unusually deep well of data to tease apart how different ways of preparing the same food affect health.

The contrast between cooking methods was stark. Frequent fry consumption was tied to a meaningfully elevated risk, but other preparations of the same vegetable showed essentially none. The finding reframes a long-running nutritional debate, suggesting that blanket warnings about potatoes miss the point: what matters is whether they are submerged in hot oil, often alongside large amounts of salt, and frequently eaten as part of fast-food meals.

The study also pointed to what people might eat instead. Swapping potatoes for whole grains was associated with a lower risk of diabetes — a reduction the researchers estimated in the range of 4% to 19% depending on the comparison. Replacing them with white rice, however, had the opposite effect, nudging risk upward. "Our findings underscore that the association between potato intake and type 2 diabetes risk depends on the specific foods used as replacement," the researchers wrote, emphasizing that substitution choices matter as much as cutting any single food.

Lead author Seyed Mohammad Mousavi and colleagues, whose work was published in The BMJ, cautioned that the study is observational and therefore cannot prove that fries directly cause diabetes; it can only establish an association. They also noted that the participants were predominantly of European ancestry and worked as health professionals, which may limit how broadly the results apply across different populations and diets.

Still, the scale and duration of the analysis make it one of the most rigorous looks yet at a question millions of people confront at the dinner table. The takeaway, the authors suggest, is reassuringly practical. Potatoes need not be banished from a healthy diet, but how often they arrive as fries — and what fills the plate when they don't — appears to make a real difference over a lifetime.