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They’re the most popular vegetable in the United States, where people eat an average of nearly 50 pounds of them a year, according to the U.S. Agriculture Department’s most recent food availability data.But the humble potato doesn’t always get the nutritional respect of say, Brussels sprouts. "Potatoes have long been associated with poor health despite being basically healthy foods,” said Marion Nestle, a molecular biologist and Paulette Goddard professor of nutrition, food studies and public health, emerita, at New York University.
Mounting evidence suggests the key to making potatoes part of a healthy diet comes down to how you cook them. In a large study from the Harvard T.H. Chan School of Public Health published this week in the BMJ, researchers found that three weekly servings of french fries were associated with a slightly higher but consistent risk, about 20 percent, of developing Type 2 diabetes, compared with eating less than one serving per week.Other potato preparations, including mashed, boiled or baked spuds, and even chips (which included both potato and corn chips), were not linked with an increased risk.
Previous studies have looked at the relationship between Type 2 diabetes and potato consumption. But older research "didn’t look at how the potatoes were prepared, like fried versus boiled or baked, or what people are eating instead,” said Seyed Mohammad Mousavi, a postdoctoral research fellow at the Harvard T.H. Chan School of Public Health and lead author on the study. His team examined data from longitudinal cohort studies spanning nearly four decades and including more than 200,000 people who did not have Type 2 diabetes when the study started.
Their findings reiterate what health experts have long stressed: Fried, ultra-processed fast foods ideally shouldn’t make regular appearances in anyone’s diet, even when their original form is a vegetable. But this study doesn’t mean potatoes need to be eliminated from your plate. Potatoes "have always been a healthy food,” said Joan Salge Blake, a clinical professor in nutrition at Boston University. "They had some bad press, but now we know it’s really just the french fry.”
Despite what you may have heard, potatoes can be nutritious
Potatoes are a starchy vegetable, which means they have a higher carbohydrate content than non-starchy options such as broccoli or lettuce.This isn’t a bad thing: The body needs carbs for energy, and potatoes are a good source, said Julia Zumpano, a registered dietitian at the Cleveland Clinic. (In fact, endurance athletes have lately been using potatoes as fuel for this reason.)
"Potatoes aren’t totally devoid of nutrients,” said Dariush Mozaffarian, a cardiologist, public health scientist and director of the Food is Medicine Institute at Tufts University. They boast a fair amount of fiber, around 3.5 grams in a small potato, as long as you leave the nutrient-rich skin on, Zumpano added.They’re a good source of vitamin C, potassium and vitamin B6, and have a small amount of protein.
The BMJ study, which referenced dietary questionnaires, focused on potato preparation but not different varieties that participants might have consumed. (And there are many, including Yukon Gold, russet and lesser-known purple potatoes.) While all can be healthy options, some might offer certain advantages. Sweet potatoes, for example, have a little more fiber than white, Zumpano noted.
Anthocyanins also feature in brightly hued purple potatoes and carotenoids in orange-fleshed sweet potatoes. These plant pigments have an antioxidant effect and may deliver additional health benefits, such as improved cognitive function and possibly even cancer prevention.
Salge Blake pointed out that a potato delivers all this nutrition while also being one of the most inexpensive vegetables per serving. "It’s a fabulous, affordable food,” she said."The price is right, and the nutrition is right.”
What is it about french fries?
What makes french fries less healthy? "First of all, most are not freshly cut potatoes,” Zumpano said. Frozen fries and even those at some restaurants are often more like "potato products,” as she put it,and could contain a long list of extra ingredients, including flour, oils, additives and color. "In a very rare case are you seeing someone slicing potatoes into wedges and putting them into a fryer.”
Then there’s the way fries are cooked, with high heat and lots of oil. "Frying [potatoes] and adding salt adds extra layers of risk,” Mousavi said. The extra oil increases the calories you take in as well as the amount of saturated fat, if they’re fried in animal fat such as beef tallow. And when you deep-fry foods at extremely high temperatures, "you induce changes in the structure of fatty acids,” Nestle explained, a process that causes unhealthy compounds to develop. (The study authors note that the composition of oil used to fry potatoes shifted during the study’s time period, from beef tallow in the 1980s to trans-fat-containing oil in the early 1990s, which was essentially banned by the Food and Drug Administration in 2018.)
Carbohydrates such as potatoes play a key role in the way the body absorbs glucose, which is where that Type 2 diabetes connection comes in. When you eat any kind of refined starch, "you’re getting a big burst of glucose in your bloodstream,” Mozaffarian explained. Glucose, or blood sugar, is necessary fuel for our bodies. But a combination of genetics and extra-high glucose over time can stress the insulin-producing cells of the pancreas, leading to Type 2 diabetes.
This is why the American Diabetes Association recommends eating "some” starchy vegetables such as potatoes as part of a balanced diet; non-starchy vegetables such as lettuce, cucumbers and broccoli don’t spike blood sugar levels as much and should make up a bigger portion of your plate.
The way french fries are cooked (with all that salt and oil) and sold (very often in enormous portions) makes them "a triple hit” for your health, Mozaffarian added. "When you’re eating a baked potato, you’re usually eating a baked potato,” Zumpano said, "but with french fries, it’s hard to quantify what you take in, and for the most part people eat very large volumes of french fries.”
Nestle pointed out that what we tend to pair french fries with doesn’t help. "People don’t eat fried potatoes on their own, usually,” she said. "They're eating hamburgers, drinking Coca-Colas, eating a lot of things that have calories.”
Potatoes that are baked, boiled or mashed usually contain less fat and sodium. (The BMJ study didn’t mention what, exactly, participants put in their non-fried potatoes, Zumpano noted. It’s possible to make any of those preparations less healthy by heaping on lots of butter, sour cream or salt.)
How to enjoy potatoes as part of a balanced diet
"People don’t have to completely cut out starches from their diet,” Mozaffarian said, "but you have to eat them wisely.” Here’s how to maximize the nutrition of your potatoes:
- Cook at home: Making your own potato dishes instead of ordering at a restaurant gives you control over how much salt, oil and fat you use. "The most effective method would be to boil or steam the potato,” said Rachele Dependahl, a registered dietitian nutritionist at Cedars-Sinai, but "you can cook it anyway you want.” If you love crispy potatoes, roasting is preferable to frying, according to USDA’s most recent Dietary Guidelines for Americans.
- Always leave the skin on: Yes, even if you’re mashing potatoes. "The skin is where most of that nutrition is packed,” Dependahl said. If you peel your potatoes, you’re throwing away excellent fiber that increases feelings of satiety, improves digestion and supports weight management, she added.
- Keep portion size in mind: Regardless of the type of starch you’re eating, they ideally should not be at the center of your plate, Mozaffarian said. When building that plate, Dependahl said she recommends patients fill one-quarter with starch such as potatoes (a fist- or baseball-size portion is a serving), one-quarter with protein and the rest with non-starchy plants.
- Before you eat potatoes, consider letting them cool: Some research has suggested cold potatoes contain higher amounts of a beneficial carbohydrate called resistant starch. "When the potato cooks and cools, the structure of the starch is reorganizing itself, and it becomes less digestible,” Dependahl explained. Since resistant starch digests more slowly, it feeds good bacteria in your gut, improving glycemic control.
- If you love french fries, try making them yourself: Experts stressed that home-cooked french fries can still be pretty good. Zumpano suggested cutting a potato into wedges, coating the wedges in avocado or canola oil, and baking in the oven. An air fryer can take a potato to another level, Dependahl added. "Just wash it, scrub it, keep the skin on, toss with some oil, some seasoning and stick it in the air fryer,” she said. "I’m telling you, people are shocked. The way it hits is different.”
