Eating French fries three times a week may raise your risk of type 2 diabetes by 20 per cent according to new research published in The BMJ.
The study found that the same amount of potatoes prepared by boiling, baking or mashing did not appear to carry the same risk.
Researchers also found that replacing potatoes with whole grains reduced diabetes risk, while swapping them for white rice increased it.
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Potatoes provide fibre, vitamin C and magnesium, but they are high in starch and have a high glycaemic index.
These factors have previously linked them to a higher risk of type 2 diabetes, although preparation method and replacement foods had not been studied in depth until now.
The findings are based on data from more than 205,000 US health professionals who were free of diabetes, heart disease and cancer at the start of the study.
They completed detailed food questionnaires every four years between 1984 and 2021.
Over nearly 40 years of follow-up, 22,299 people developed type 2 diabetes.
After accounting for lifestyle and dietary factors, researchers found that:
- Three weekly servings of total potatoes were linked to a 5 per cent increase in diabetes risk
- Three weekly servings of French fries were linked to a 20 per cent increase in diabetes risk
- Boiled, baked or mashed potatoes were not linked to a significant increase in risk
Replacing three weekly servings of total potatoes with whole grains reduced diabetes risk by 8 per cent. Swapping French fries for whole grains reduced risk by 19 per cent. Replacing potatoes with white rice was linked to a higher risk.
The researchers emphasise that the study is observational and cannot prove cause and effect.
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They also note that most participants were white health professionals, so the findings may not apply to all groups.
In an editorial, experts said baked, boiled or mashed potatoes can be part of a healthy diet, particularly if whole grains remain a priority.
They added that potatoes have a relatively low environmental impact compared with many other staple foods.
Future studies should include more diverse populations and take preparation methods into account.
