Eating french fries comes with an unexpected health risk

A new study that tracked more than 205,000 U.S. adults for almost 40 years reports a 20 percent rise in type 2 diabetes among people who eat french fries three times a week.

The same analysis found no meaningful change in diabetes rates for similar amounts of baked, boiled, or mashed potatoes. This suggests that preparation, not the potato itself, influences diabetes risk.

Cooking styles and diabetes risk

Study lead author Seyed Mohammad Mousavi of the Harvard T.H. Chan School of Public Health noted that his team wanted to separate cooking style from the crop itself. Boiling or baking leaves the tuber’s structure mostly intact, so more starch resists quick digestion.

That slower breakdown keeps blood sugar steadier, while deep frying breaks starch granules and surrounds them with fat, pushing their glycemic index higher.

Because the index measures how fast a food raises glucose, a higher value can translate into more insulin demand and, over time, greater metabolic strain.

French fries raise diabetes risk

“Small changes in our daily diet can have an important impact on risk of type 2 diabetes,” said Walter Willett, professor of epidemiology and nutrition. He recommended swapping a side of fries for a salad or whole grain roll.

Deep fried potatoes often arrive salted, sometimes battered, and usually cooked in oils repeatedly heated – creating compounds that may harm pancreatic cells.

Portion size matters too, because a restaurant “serving” can exceed two cups, far more than the study’s single cup baseline.

Whole grains lower diabetes risk

Replacing any potato dish with three weekly servings of whole grains trimmed diabetes risk by up to 8 percent, and the drop hit 19 percent when the swap targeted fries.

Whole grain kernels carry fiber, magnesium and phytochemicals that blunt glucose spikes and may improve insulin sensitivity. They also displace refined starches, lowering overall dietary glycemic load.

Participants who regularly chose oats, farro or true whole grain bread tended to exercise more and smoke less, but the researchers adjusted for these habits. The protective link remained after lifestyle factors were stripped away.

White rice also raises risk

When the same models substituted white rice for potatoes, diabetes odds crept upward, a pattern echoed in a 2012 meta analysis of four continents.

White rice loses bran and germ in milling, leaving almost pure starch that digests quickly.

Its high glycemic index mirrors that of fries, offering little metabolic advantage. Brown rice fared better but was not the standout that whole grain wheat products proved to be, possibly because it contains less fiber per gram.

Tracking the diet and diabetes link

Mousavi’s team pooled data from three well-known cohorts: the Nurses’ Health Study, Nurses’ Health Study II and the Health Professionals Follow up Study, covering 5.2 million person years.

Dietary questionnaires repeated every four years enabled the researchers to examine how habits changed, reducing the error that plagues one time food recalls.

The team adjusted for weight, smoking, exercise, alcohol use, family history and dozens of dietary variables, yet the fry signal persisted. Even after carving out early cases to avoid reverse causation, the 20 percent excess risk stood firm.

French fries vs. boiled potatoes

The researchers point to several factors that might explain why fries, but not boiled or baked potatoes, show a clear link with higher diabetes risk.

Frying increases calorie density, changes starch structure, and introduces compounds formed at high heat that can harm insulin function over time.

Another factor could be what typically accompanies fries. They are often eaten alongside processed meats, sugary drinks, or refined breads, creating a meal pattern with a higher overall glycemic load and saturated fat intake. This broader dietary context may compound the effects seen in the study.

Tips for healthier fries

The experts recommend to choose potatoes that preserve their skin, keep added fat modest, and pair them with vegetables or protein to slow digestion.

Cold potato salad made from boiled tubers delivers resistant starch, which further tempers post meal glucose.

You don’t have to give up fries completely, but eating them less often and in smaller amounts can help lower your risk. Instead of a cup of fries, try a cup of barley, quinoa, or air-fried potato wedges to keep your meals tasty without hurting your health.

The study is published in the journal The BMJ.

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