Which Is Better for Your Blood Sugar?

Good news, spuds lovers: Research shows that, although regularly eating French fries increased blood sugar levels and type 2 diabetes risk, eating potatoes in other forms—such as mashed, baked, or boiled—did not.

The study, published in The BMJ in August, also revealed that replacing any form of potatoes with whole grains could lower the likelihood of developing the disease.

Diet plays a major role in the development and management of type 2—and potatoes have long been dogged by a reputation for being bad for blood sugar. Because they’re high in carbohydrates and have a high glycemic index (i.e., how quickly they raise blood sugar), many people with type 2 diabetes avoid them. But existing research supporting this rationale has a flaw.

“One big issue was that many of those studies didn’t look at how the potatoes were prepared—like fries versus boiled—or what people were eating instead,” study author Seyed Mohammad Mousavi, PhD, a postdoctoral research fellow at Harvard University, told Health.

His team wanted to take a more nuanced look at the connection between potato consumption and diabetes risk. Using data from three ongoing research programs, researchers followed over 200,000 health professionals for up to 36 years, regularly collecting detailed information about their diets and lifestyles. Dietary questionnaires showed the frequency with which they consumed French-fried, baked, boiled, or mashed potatoes. It also tracked their intake of whole grains.

By comparing this data with the number of new diagnoses of type 2 diabetes, the researchers determined that three servings weekly of French fries increased the risk of developing type 2 diabetes by 20%. Baked, boiled, and mashed potatoes, on the other hand, were not significantly associated with an elevated risk.

Meanwhile, swapping potatoes for whole grains had an even more positive outcome. Replacing three servings weekly of total potatoes with whole grains like whole wheat pasta, bread, or farro was estimated to lower the type 2 diabetes rate by 8%. Exchanging servings of French fries for whole grains lowered the rate by 19%.

When it comes to potatoes health, the cooking method can have a big influence.

“The nutrient composition of food can change during preparation and cooking,” Alyssa Tindall, RD, PhD, an assistant professor of health sciences at Ursinus College, told Health. “For example, deep frying food, such as in the case of potatoes to make French fries, increases the fat content of the food, which can impact digestion, absorption, and disease risk.”

According to Mousavi, the oils and temperatures used for frying are major culprits here. “French fries are usually deep-fried at very high temperatures, often in oils that—during much of our study period—contained trans fats and produced other harmful compounds,” he said.

Cooking oils at extremely high temperatures can create oxidation, a driver of inflammation that may contribute to the development of type 2 diabetes.

On the other hand, cooking methods like baking, boiling, and mashing don’t usually add these elements. For this reason—and considering their beneficial nutrients like fiber and potassium—non-fried potatoes may actually improve diet quality in people with type 2 diabetes. In fact, the American Diabetes Association says potatoes can fit on a diabetes-friendly meal plan.

Besides keeping French fries to a minimum, a host of other dietary strategies can help prevent type 2 diabetes. According to the National Institute of Diabetes and Digestive and Kidney Diseases, best practices include:

Eating smaller portions of foods that are high in calories, fat, and sugar.
Drinking water instead of sweetened drinks like soda, sports drinks, and fruit juice.
Choosing foods with less trans fat, saturated fat, and added sugars.
Making healthy swaps where possible (subbing a baked potato for French fries is one good example).

Made consistently, these and other simple choices add up to risk reduction. “You don’t have to give up your favorite foods, but small changes—like eating fries less often, baking instead of frying, and choosing whole grains as your primary source of carb—can make a real difference for your long-term health,” said Mousavi.