People who eat three portions of French fries a week have a higher risk of developing type 2 diabetes, a new study suggests. Those who consume similar amounts of boiled, baked or mash potatoes do not have an increased risk, researchers found.

An international team of researchers, including an expert from the University of Cambridge, wanted to investigate any links between potato consumption and the risk of type 2 diabetes. Academics analysed data on 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.

And during the study follow-up periods, some 22,000 cases of type 2 diabetes were documented.

Overall the research team found that consumption of baked, boiled or mashed potatoes were not linked to an increased risk of type 2 diabetes (T2D).

But people who had a higher consumption of French fries - at least three weekly servings - had a 20% increased risk.

And those who eat fries five times a week appeared to have a 27% increased risk.

"The risks associated with potato intake varied by cooking method," the authors wrote in The BMJ.

"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%.

"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 performed a review of all of 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."