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t’s not just the French fries that are bad for you. A new study finds that eating boiled, baked, fried, or mashed potatoes four or more times a week is associated with an increased risk of high blood pressure — but questions remain.

Why it matters:

Potatoes are among the most commonly eaten foods in the world. Each American consumed on average 100 pounds of potatoes in 2014, according to the National Potato Council.

The nitty-gritty:

Researchers combined the data from three big population studies amounting to over 187,000 American men and women in the US who were surveyed for more than 20 years. Participants answered questionnaires about their dietary intake, including their frequency of potato consumption. They also reported if they were diagnosed with hypertension.

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When researchers analyzed the data, they found that those who ate four or more servings a week of baked, boiled, or mashed potatoes were 11 percent more likely to develop hypertension than those who ate less than one serving a month. For those eating French fries four or more times a week, that rose to 17 percent more likely. However, consumption of potato chips wasn’t associated with any increased risk. The findings were published in the BMJ.

You’ll want to know:

“Potatoes have a very high glycemic index, which means that after a meal, there is this increase in blood glucose, which is a precursor to hypertension,” explained Dr. Lea Borgi, a physician at Brigham and Women’s Hospital and one of the study’s authors.

But potatoes aren’t all bad. “Potatoes are high in potassium,” said Connie Weaver, a professor of nutrition science at Purdue University, who was not involved with the study. “There are other analyses that show that potassium in your diet lowers your blood pressure. So, does the risk of eating potatoes outweigh the benefit of nutrients like potassium? I’m not sure.”

The study also found that replacing one serving a day of baked, boiled, or mashed potatoes with one serving a day of non-starchy vegetables was associated with decreased risk of hypertension.

But keep in mind:

The study was just observational, and can’t establish cause and effect. Researchers used statistical methods to control for some possibly confounding variables, including body mass index, race, family history of hypertension, physical activity, and other dietary habits. Still, the groups may have been different in ways not controlled for.

“With any observational study, there’s a possibility of missing something,” said Borgi. “In our model we tried to take everything into account.”

Also participants self-reported potato consumption every four years, recalling their intake over the past year, which could introduce recollection bias.

Finally, there were some statistical oddities in the paper that indicate its results should be taken with a grain of salt. The hypertension risk of baked, boiled, or mashed potatoes was seen in women, but not in men, which doesn’t have a clear explanation. What’s more, men had a lower risk of hypertension if they ate more potato chips — likewise a head-scratcher.

The bottom line:

Broader dietary patterns are likely more important than individual foods or nutrients. Still, dietary guidelines urge people to limit their consumption of starchy vegetables, and for a variety of health reasons, that’s still a good idea.

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