Eating three portions of French fries a week raises the risk of developing type 2 diabetes by 20 per cent, a new study suggests.
That risk increases to 27 per cent for people who eat fries five times a week.
However, those who eat similar amounts of boiled, baked or mashed potatoes do not have an increased risk, researchers found.
An international team of researchers wanted to investigate any links between potato consumption and the risk of type 2 diabetes (T2D).
Potatoes contain several nutrients, including fibre, vitamin C and magnesium, but they also have a high starch content and therefore a high glycemic index, which is linked to diabetes.
Academics analysed data from studies tracking the health of more than 205,000 health workers in the US. Repeated surveys about people’s diets were performed over almost four decades.
During the study follow-up periods about 22,000 cases of type 2 diabetes were documented.
According to the researchers, while previous studies hinted at a link between potatoes and T2D, the evidence was inconsistent. It often lacked detail of cooking methods and the potential effects of substituting other foods for potatoes.
“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,” said lead author Seyed Mohammad Mousavi, postdoctoral research fellow in the Department of Nutrition at Harvard University.
“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?”
Writing in the The BMJ, the authors said: “The risks associated with potato intake varied by cooking method.
“The association between higher potato intake and increased T2D risk is primarily driven by intake of French fries.
“Higher intake of French fries, but not combined baked, boiled or mashed potatoes, was associated with a higher risk of T2D.”
The research team also found that replacing three servings of potatoes each week with whole grains was found to lower the risk of type 2 diabetes by 8 per cent.
“Replacing any form of potatoes, particularly French fries, with whole grains is estimated to lower the risk of T2D, reinforcing the importance of promoting whole grains as an essential part of a healthy diet,” they wrote.
But replacing potatoes with white rice was associated with an increased risk of type 2 diabetes, they found.
The research team also reviewed all the other studies on the topic which had similar findings.
In a linked editorial, also published in The BMJ, experts from the US and Denmark wrote: “This finding also corresponds to the observed associations between high intake of ultra-processed foods and high risk of type 2 diabetes – French fries are often ultra-processed, whereas baked, boiled or mashed potatoes are often minimally processed.”
They added: “With their relatively low environmental impact and their health impact, potatoes can be part of a healthy and sustainable diet, though whole grains should remain a priority.”
Commenting on the study, Dr Faye Riley, research communications lead at Diabetes UK, said: “This research shows that the link between potatoes and type 2 diabetes isn’t as clear-cut as it might seem.
“Type 2 diabetes is a complex condition, with many factors influencing its development, including genetics, age and ethnicity.
“Diet is just one part of the picture, but this study suggests that how food is prepared can make a difference and reinforces the advice to prioritise whole grains and cut back on fried or heavily processed foods as a way to support a balanced diet and reduce your risk.”
