French Fries and Diabetes: A Major New Study Says It's Not Potatoes That Are the Problem

If you've been told to avoid potatoes because of diabetes, new research suggests that advice may need a serious update — because not all potatoes are created equal.

A large study published in The BMJ tracked more than 205,000 U.S. health professionals over nearly 40 years and found that eating three servings of French fries per week was linked to a 20% higher risk of developing type 2 diabetes, while baked, boiled, or mashed potatoes showed no significant increase in risk. It's one of the most comprehensive looks at potato consumption and diabetes risk ever conducted, and its findings could reshape how people managing or preventing type 2 diabetes think about their carbohydrate choices.

Why Potatoes Got a Bad Reputation

Potatoes have long been a complicated food in the diabetes world. They provide important nutrients, including fiber, vitamin C, and magnesium — but they're also rich in starch and have a relatively high glycemic index, meaning they can cause blood sugar levels to rise quickly. Because of this, earlier research has generally painted all potatoes with the same brush, linking potato consumption broadly to a greater risk of type 2 diabetes. But researchers behind this new study argued that two critical factors had been routinely overlooked: how the potato is prepared, and what food it replaces in the diet.

What the Data Actually Showed

The study drew on data from more than 205,000 U.S. health professionals who participated in three major long-term studies conducted between 1984 and 2021. None of the participants had diabetes, heart disease, or cancer at the start of the study. Every four years, they completed detailed dietary questionnaires, and during nearly 40 years of follow-up, 22,299 participants developed type 2 diabetes.

After controlling for lifestyle and dietary variables, researchers found that every three weekly servings of potatoes overall were associated with a 5% increase in the rate of type 2 diabetes — but the strongest signal by far came from French fries, which were linked to a 20% increase. Baked, boiled, or mashed potatoes in similar quantities were not associated with a statistically significant increase.

The Replacement Effect: This Part Really Matters

Perhaps the most actionable finding in the study involves what people eat instead of potatoes. Replacing three weekly servings of potatoes with whole grains was associated with an 8% lower rate of type 2 diabetes. When French fries specifically were swapped for whole grains, that figure jumped to a 19% lower rate.

The flip side is equally important for anyone managing blood sugar. Substituting either total potato intake or baked, boiled, or mashed potatoes with white rice was associated with a higher rate of type 2 diabetes — a finding that may surprise people who consider rice a safer carbohydrate swap.

What This Means for People With Diabetes

An accompanying editorial published alongside the study made the case that potatoes should stop being treated as a single category. Researchers emphasized that both preparation methods and replacement foods are important factors when making dietary recommendations, and noted that baked, boiled, and mashed potatoes can fit into a healthy and environmentally sustainable diet because of their relatively low environmental impact and overall nutritional value. That said, the authors noted that whole grains should remain a priority food choice for reducing diabetes risk.

For people with type 2 diabetes or those at risk, the practical takeaway is fairly straightforward: a boiled or baked potato isn't the enemy. The problem is what it becomes when it's deep-fried, and what it replaces on the plate when whole grains get crowded out.

The Bottom Line

Because this was an observational study, it cannot prove that French fries directly cause diabetes, and the researchers acknowledge that other factors not measured in the study may have contributed to the results. The study population was also predominantly health professionals of European ancestry, which means the findings may not apply equally to all populations.

Still, the evidence adds meaningfully to a growing body of research supporting a food-as-medicine approach to diabetes prevention and management — one where the how of eating matters just as much as the what.

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This content is for informational purposes only and should not be taken as medical advice. Always consult a qualified healthcare provider about any questions or concerns regarding your health or treatment options.