Potatoes are the most commonly consumed vegetable in the U.S., yet they often get a bad rap. Most are eaten the form of fries or chips, so many people consider them an unhealthy food.

It doesn’t have to be that way.

Eating one medium-size potato a day can be part of a healthy diet and doesn’t increase cardiometabolic risk — the chances of having diabetes, heart disease or stroke — as long as the potato is steamed or baked, and prepared without adding too much salt or saturated fat, a study by nutritionists at The Pennsylvania State University found.

Consuming non-fried potatoes also led to higher potassium and fiber intake compared to eating refined grains, like white rice, white bread or pasta, they noted. The results were published last month in the British Journal of Nutrition.

“Certainly eating chips or french fries should be discouraged, but there are healthy ways to prepare potatoes, so I do think that lumping them all together is a little bit unfair to the poor potato,” Emily Johnston, study co-author and a doctoral student in the department of nutritional sciences at Penn State, told TODAY.

“We don’t want people to fear the potato, but we want to make sure that they eat it in a healthful way and in a controlled portion size.”

For the study, researchers looked at the effect of eating potatoes every day, compared to eating the same number of calories in refined grains.

They recruited 50 healthy adults, whose baseline blood pressure and arterial stiffness were measured at the start of the study, and whose blood samples were checked for fasting glucose, cholesterol, insulin and other markers. Those checks were repeated throughout the study.

The participants were then randomly assigned to replace their usual main meal starchy side dish with a study side dish: either 200 calories worth of potatoes or refined grains, as prepared by the Metabolic Diet Study Center at Penn State. They ate this way every day for four weeks.

After a break of at least two weeks, they switched to the opposite study side dish, eating it with their main meal every day for a month.

Potato side dishes consisted of steamed or baked red, white and gold spuds. Refined grain options included Spanish rice, pasta, garlic bread and naan, Johnston said.

All were prepared with minimal added salt, saturated fat or sugar, though some ingredients were minimally added for taste, including scallions, onions, breadcrumbs and cheese.

The participants’ potassium and fiber intake was significantly higher when they ate potatoes, compared to refined grains, the study found. Their diet quality was also higher, driven by a higher vegetable intake.

There was no evidence eating potatoes increased fasting glucose levels, and there was no difference in cholesterol, insulin or other markers, the authors noted. There were no adverse cardiometabolic consequences, they concluded.

Potatoes are a rich source of potassium, which is important for blood pressure regulation, but which most Americans don’t get enough of in their diet, Johnston said.

Almost half of adults in the U.S. have hypertension, according to the Centers for Disease Control and Prevention.

“We certainly want people to eat more non-starchy vegetables because we know the average American intake is well below recommendations,” Johnston said.

“But starchy vegetables and refined grains do contribute some important nutrition as well, it’s just that we need to make sure we eat them in balance.”

The Alliance for Potato Research and Education, a non-profit funded by the potato industry, provided money for the study, but didn’t have any say in any aspects of it, the authors wrote.

Potatoes can be part of a healthy diet, including one for weight loss, noted NBC News Health and Nutrition Editor Madelyn Fernstrom. She called them “a nutritional powerhouse,” with a medium baked potato containing 4 grams of fiber (about 20% of your daily count), 4 grams of protein, half of your vitamin C for the day, 25% of your potassium, a third of your vitamin B6, and nearly 10% of your iron.

• Make potatoes a side dish composing about one-fourth of your whole plate, Fernstrom advised.
• Be careful about the portion size: One medium potato is about the size of a computer mouse, Johnston noted. Restaurant baked potatoes can be much bigger, so consider eating half.
• Stick to baking, roasting or steaming: Boiling potatoes doesn’t add any calories or fat, but it leaches potassium out of them. Frying is a nutritional deal-breaker.
• Whether you bake or microwave, keep the skin on to optimize the nutrients and fiber.
• Skip the extras: Don’t load your potato up with butter, sour cream or bacon bits. Go easy on the salt.