Fries May Be Delicious—But They Could Be Raising Your Diabetes Risk, Study Warns

Love French fries? You might want to slow your roll—especially if you’re hitting the drive-thru a few times a week.

A massive new study out of Harvard found that eating French fries three or more times a week is linked to a 20% higher risk of developing type 2 diabetes. But here’s the twist: baked, boiled, or mashed potatoes? No such risk.

“Not all potatoes are created equal,” said Seyed Mohammad Mousavi, the study’s lead author and a research fellow at Harvard’s T.H. Chan School of Public Health. “It’s really the way they’re prepared that makes the difference.”

The study, published in the British Medical Journal, crunched nearly 40 years of diet data from over 200,000 health workers in the US Researchers tracked what people were eating and how their health changed over time. In that period, more than 22,000 people developed type 2 diabetes—and fry lovers stood out.

Plain potatoes aren’t the villain here. It’s when they get dunked in hot oil—often filled with saturated or trans fats—that things go south. Deep-frying bumps up the calories, can fuel insulin resistance, and sets the stage for weight gain, inflammation, and eventually diabetes.

“In the US, portion sizes are huge. So even if you’re just having fries once a week, it could still be a hefty amount,” said Walter Willett, a co-author on the study and longtime Harvard nutrition expert.

And yes, even “once a week” can add up. That medium McDonald’s fry? It’s already a full serving.

Good question. This study didn’t specifically look at sweet potatoes, but they do tend to have a lower glycemic index, meaning they don’t spike your blood sugar as fast. Still, they’re not totally in the clear—especially when deep-fried and salted to oblivion. More research is needed, but moderation is key.

The research team didn’t just ring the alarm—they offered solutions. Swapping French fries for whole grains—like farro, quinoa, or whole-grain bread—can cut your diabetes risk by nearly 20%.

Even replacing baked or mashed potatoes with whole grains dropped risk by 4%. But oddly enough, switching to white rice had the opposite effect and increased diabetes risk, likely because of rice’s high glycemic index.

Don’t panic if fries are your guilty pleasure. Mousavi says it’s all about how you cook them and how often you indulge.

• Try baking or air-frying fries at home with a bit of olive oil.
• Watch your portions (maybe skip the supersize).
• Pair your fries with a salad, not another pile of carbs.
• Skip the cheese, bacon, and heavy sauces that pile on the calories and fats.

Also important: Your overall diet matters more than any one food. A colorful plate packed with veggies, whole grains, lean protein, and healthy fats will do far more for your long-term health than obsessing over the occasional snack.

“Small everyday choices add up,” Mousavi said. “The point isn’t to fear fries—it’s to think about the bigger picture.”

So go ahead, enjoy your fries—just maybe not every time you see them on the menu.

With input from BBC,  NBC News, and National Geographic.