Eating just three servings of French fries a week may raise the risk of type 2 diabetes by 20%, new research in The BMJ has found, but potatoes prepared in other ways, such as boiled, baked, or mashed, do not appear to have the same effect.
The study, which tracked over 205,000 US health professionals for up to 40 years, recorded more than 22,000 cases of type 2 diabetes.
After adjusting for lifestyle and diet, researchers found a modest 5% increase in risk for each three weekly servings, but a much sharper rise for French fries.
Replacing potatoes with whole grains lowered diabetes risk by 8% for total potatoes and 19% when swapping fries, while substituting with white rice increased risk.
Potatoes, while rich in fibre, vitamin C, and magnesium, also have a high glycemic index. Researchers stressed that both the cooking method and the food used as a replacement were key to understanding their health impact.
Most participants were white and in the health profession, so findings may not apply to all populations. And as an observational study, it cannot prove cause and effect.
A linked editorial says baked, boiled, or mashed potatoes can form part of a healthy, sustainable diet, especially if whole grains remain a dietary priority. The authors called for further studies in more diverse groups.
The findings, researchers say, highlight a simple dietary trade-off: keep the spuds, lose the fryer, and choose whole grains over refined carbs like white rice.
