The findings threaten to undermine government healthy meals programs, such as the UK’s Government’s Eatwell guide that includes potatoes as part of the starchy carbohydrates section
Notably, on the international front, the World Health Organisation (WHO) does not include potatoes as vegetables.
The association of potatoes intake with high blood pressure (hypertension) has not previously been studied. Potatoes are naturally high in potassium and a study found potassium supplementation beneficial for prevention of hypertension.
In contrast another study found a diet rich in protein or monounsaturated fat reduced blood pressure compared with diets rich in carbohydrates.
The team at Brigham and Women's Hospital and Harvard Medical School began looking at the long-term effects of eating baked, boiled, or mashed potatoes. The consumption of French fries, and potato chips (crisps) was also investigated.
Data from 187,000 men and women from three large studies over 20 years was analysed. Details of their diet that included potato consumption were collected via a questionnaire. Hypertension in subjects was confirmed by medical diagnosis.
The researchers found that four or more servings a week of baked, boiled or mashed potatoes were linked to an increased risk of hypertension compared with less than one serving a month in women, but not in men.
Eating more French fries was also linked to an increased risk of hypertension in both women and men. However, consumption of potato chips (crisps) did not appear to increase risk.
Commenting on their findings, the researchers thought that there were ‘potentially important public health ramifications.’
“The results do not support a potential benefit from the inclusion of potatoes as vegetables in government food programs but instead support a harmful effect that is consistent with adverse effects of high carbohydrate intakes seen in controlled feeding studies."
In explaining the findings, the authors pointed towards potatoes’ high glycaemic index that compared with other vegetables, could result in sharp rises in blood sugar levels.
They recommended replacing one serving a day of boiled, baked, or mashed potatoes with one serving of a non-starchy vegetable that have been linked to a decreased risk of hypertension.
Critics of the study immediately questioned the significance of these results arguing that the study could only show an association, not cause and effect.
“We therefore can’t conclude that potatoes cause high blood pressure and we cannot explain the cause of the results seen in the study,” said Victoria Taylor, senior dietitian at the British Heart Foundation.
“This is a study from the US where dietary guidance and recommendations vary from the UK, where potatoes are not included in the 5-a-day recommendations for fruit and vegetable consumption. We must remember that, as with all foods, it’s important to consider the overall balance of the foods we eat.”
Echoing her comments, Professor Tom Sanders, emeritus professor of Nutrition and Dietetics at King’s college London, said: “This report is an observational study not a dietary intervention trial.”
“Potatoes do contain small amounts of alkaloids such as chaconine and solanine but not in sufficient amounts to affect blood pressure. However, potatoes, especially chips, are often consumed with added salt which may be part of the explanation for this association with raised blood pressure.”
Source: British Medical Journal
Published online ahead of print, DOI: 10.1136/bmj.i2351
“Potato intake and incidence of hypertension: results from three prospective US cohort studies.”
Authors: Lea Borgi, Eric Rimm, Walter Willett, John Forman.