Eating three servings of French fries a week is associated with a 20% increased risk of developing type 2 diabetes, but eating similar amounts of potatoes cooked in other ways — boiled, baked or mashed — does not substantially increase the risk, finds a study published by The BMJ on August 6.
What’s more, replacing any form of potatoes with whole grains was associated with a lower type 2 diabetes risk, but swapping them for white rice was linked to an increased risk, the results show.
Potatoes contain several nutrients including fiber, vitamin C, and magnesium, but they also have a high starch content and therefore a high glycemic index, so have been linked to a higher risk of developing type 2 diabetes.
But neither the preparation method for potatoes nor specific foods that potatoes would replace have been considered, both of which are key to evaluating the overall health impact of potatoes.
To address this, researchers investigated the association between intake of potatoes prepared by different methods (boiled, baked, or mashed versus French fries) and risk of type 2 diabetes. They also looked at the impact on health of replacing potatoes with other major carbohydrates, such as whole grains and rice.
Their findings are based on more than 205,000 health professionals from three large US studies carried out between 1984 and 2021. Participants were free of diabetes, heart disease or cancer and completed detailed food questionnaires every four years.
During almost 40 years of follow up, 22,299 people were diagnosed with type 2 diabetes.
After adjusting for lifestyle and dietary factors related to diabetes risk, the researchers found that for every three weekly servings of total potato, the rate of type 2 diabetes increased by 5% and for every three weekly servings of French fries, the rate increased by 20%. However, similar intake of baked, boiled, or mashed potatoes was not associated with a significantly increased risk.
Replacing three weekly servings of total potato with whole grains lowered the type 2 diabetes rate by 8%. Substituting baked, boiled, or mashed potatoes with whole grains lowered the rate by 4%, and replacing French fries lowered the rate by 19%.
In contrast, replacing total potatoes or baked, boiled, or mashed potatoes with white rice was associated with an increased risk of type 2 diabetes.
This is an observational study so no firm conclusions can be drawn about cause and effect and the researchers can’t rule out the possibility that other unmeasured factors may have influenced their results. Most participants were also health professionals of European ancestry, so findings may not apply to other populations.
Nevertheless, they conclude: “Our findings underscore that the association between potato intake and type 2 diabetes risk depends on the specific foods used as replacement. 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.”
So, are potatoes back on the plate? Well, it depends, say researchers in a linked editorial, who note that it is important to consider preparation method and replacement food when guiding the public or informing policy.
They point out that with their relatively low environmental impact and their health impact, baked, boiled, or mashed potatoes can be part of a healthy and sustainable diet, though whole grains should remain a priority, but say future studies from more diverse populations that account for both preparation methods and substitution analysis are needed.