Potato prep matters: Fries linked to highest diabetes risk

French fries are linked to a higher risk of developing type 2 diabetes, according to new Harvard research. The study draws ties between consuming potatoes and diabetes risk, suggesting outcomes are heavily influenced by what specific cooking method is used and what whole foods are replaced.

In contrast, the diabetes risk was reduced by swapping any kind of cooked potato with whole grains. 

Notably, the study found that three servings weekly of French fries are associated with a 20% excess risk of developing type 2 diabetes.

The researchers say that this association is independent of lifestyle and dietary factors.

“Our study offers deeper, more comprehensive insights by looking at different types of potatoes, tracking diet over decades, and exploring the effects of swapping potatoes for other foods,” says lead author Seyed Mohammad Mousavi, postdoctoral research fellow in the Department of Nutrition.

“We’re shifting the conversation from, ‘Are potatoes good or bad?’ to a more nuanced — and useful — question: How are they prepared, and what might we eat instead?”

The team examined the diets and diabetes outcomes of 205,107 men and women over 30 years (1984 and 2021). Within almost 40 years of follow-up, 22,299 people were diagnosed with type 2 diabetes.

Baked, boiled and mashed potatoes

In contrast to French fries, the study found that other cooked potato varieties do not pose a significant risk of diabetes progression. It maintains that there is no significant risk associated with the consumption of baked, boiled, or mashed potatoes.

The researchers note potatoes, in these forms, contain essential nutrients like fiber, vitamin C, and magnesium.

One key finding is the health benefit of replacing potatoes with other foods. The researchers calculated that eating whole grains — such as whole-grain pasta, bread, or farro — instead of baked, boiled, or mashed potatoes, could reduce the risk of type 2 diabetes by 4%.

Meanwhile, they say replacing French fries with whole grains could bring type 2 diabetes risk down by 19%.

Moreover, replacing three weekly servings of total potatoes with whole grains lowered the type 2 diabetes rate by 8%. The authors caution: “Replacing total potatoes or baked, boiled, or mashed potatoes with white rice was associated with an increased risk of type 2 diabetes.”

The study found no significant risk associated with baked, boiled, or mashed potatoes.Small changes go far

The study participants regularly responded to dietary questionnaires, detailing the frequency with which they consumed certain foods, including baked, boiled, or mashed potatoes, French fries, and whole grains.

“Small changes in our daily diet can have an important impact on the risk of type 2 diabetes. Limiting potatoes — especially limiting French fries — and choosing healthy, whole-grain sources of carbohydrate could help lower the risk of type 2 diabetes across the population,” underscores Walter Willett, professor of epidemiology and nutrition and a corresponding author on the Harvard study.

The researchers note this is an observational study, meaning no firm conclusions can be drawn about cause and effect. Additionally, they cannot rule out the possibility that other unmeasured factors may have influenced their results.

In addition, most participants were health professionals of European ancestry, so the authors say their findings may not apply to other populations.

Nevertheless, they conclude: “The findings also align with current dietary recommendations that promote the inclusion of whole grains as part of a healthy diet for the prevention of type 2 diabetes.”

The study is published in The BMJ and led by the Harvard T.H. Chan School of Public Health. 

Diabetes in research

A recent study found that consuming one artificially sweetened soft drink each day could raise a person’s risk of developing type 2 diabetes by 38%. The paper suggests this risk could be higher than it is for consumers of sugar-sweetened beverages, such as regular sodas, where the threat was said to be 23% greater.

This month, scientists discovered a molecule, D-lactate, produced by gut bacteria, which enters the bloodstream and fuels the liver to make more glucose and fat than necessary. They believe this opens new pathways to improving blood sugar levels and reducing liver damage when treating metabolic diseases like type 2 diabetes and fatty liver disease.

Meanwhile, researchers have identified a new subtype of diabetes in children and young adults in sub-Saharan Africa, suggesting that many patients are not receiving the optimal treatment for their condition. The discovery was made through the largest study of its kind in the region, raising concerns that many patients across the continent, and potentially globally, may require updated diagnoses to access the best treatment.