French Fries May Raise Your Diabetes Risk

Potatoes may be a dinner staple, but they’ve long carried a mixed reputation—a nutrient-rich vegetable to some and a boring, unhealthy carb to others.

A new analysis published in The BMJ suggests it’s not the potato itself, but how it’s cooked and what you eat instead that matters. French fries were linked to a higher risk of type 2 diabetes, while baked, boiled or mashed potatoes were not. Swapping potatoes—especially fries—for whole grains lowered that risk, but replacing them with refined carbs like white rice pushed it higher.

Potatoes offer nutritional value, supplying vitamin C, potassium, B vitamins, fiber and antioxidants, especially when eaten with the skin. But their high glycemic index, which can spike blood sugar, has kept them under scrutiny in diabetes research. Earlier studies were mixed, though many pointed to fried potatoes as the bigger concern. This new study offers a clearer view by separating preparation methods and modeling healthier swaps.

How Was the Study Conducted?

Researchers from the Harvard T.H. Chan School of Public Health analyzed about 30 years of diet and health data from more than 205,000 U.S. adults taking part in three major long-term studies—the Nurses’ Health Study, Nurses’ Health Study II and the Health Professionals Follow-up Study. All were health care workers and healthy when the research began. Every two to four years, they filled out detailed food questionnaires that included questions on how often they ate different kinds of potatoes, from French fries to baked, boiled or mashed.

Over time, the team identified new cases of type 2 diabetes through follow-up questionnaires. They used statistical models to account for factors such as age, weight, lifestyle and overall diet so they could better isolate the role potato consumption might play in diabetes risk. They also examined how risk might change if potatoes were replaced with other carbohydrate sources.

What Did the Study Find?

Over the course of the study, 22,299 participants developed type 2 diabetes. Those who ate more potatoes overall tended to be less active, consume more calories and have lower diet quality, with higher intakes of red meat, refined grains and sugary drinks. Baked, boiled or mashed potatoes were eaten much more often than French fries.

After the researchers took those other lifestyle and diet factors into account, they found a clear pattern. Eating three extra servings of potatoes each week was linked to about a 5% higher rate of type 2 diabetes. The increase was much steeper for French fries, at around 20%, while baked, boiled or mashed potatoes did not show a significant change in risk.

When the researchers modeled different food swaps, they saw a similar pattern. Replacing three weekly servings of potatoes with whole grains lowered diabetes rates by about 8%. Making the same swap from fries cut the rate by about 19%. Swapping baked, boiled or mashed potatoes for whole grains resulted in a smaller 4% drop. However, replacing potatoes with white rice was linked to a higher risk.

It’s worth keeping in mind that this was an observational study, so it can’t prove that French fries directly cause type 2 diabetes. The findings show an association, meaning other unmeasured habits or health factors could still play a role in the results, even with adjustments for lifestyle and diet.

How Does This Apply to Real Life?

This study isn’t telling you to give up potatoes. Instead, it’s a reminder to pay attention to how you prepare them and what you eat alongside them. Boiled, baked or mashed potatoes can be part of a healthy routine, especially when they’re paired with vegetables, healthy fats and protein.

French fries are best enjoyed as occasional enjoyment rather than a staple. Having them once in a while is fine, but making them a frequent part of your meals can tip the balance away from your health goals.

If you want to make a healthier swap, whole grains like quinoa, farro, barley or brown rice are solid choices. Replacing potatoes with refined carbs—especially white rice—can push your risk in the opposite direction.

Our Expert Take

This study found that French fries, but not baked, boiled or mashed potatoes, were linked to a higher risk of type 2 diabetes—and swapping fries or total potatoes for whole grains lowered that risk. Your overall eating habits, activity level and body weight still matter more for long-term health than any single food. Potatoes can be part of a balanced diet—it’s how they’re prepared and how often you eat them that makes the difference.