What’s best way to prepare veggies?

In Carlene Thomas’ experience, two types of people ask her advice as a dietitian about the healthiest way to prepare vegetables.

Those looking to improve their diet are curious about how different cooking methods affect nutritional content. Others wonder how best to work more vegetables into their diet in general.

The simplest version of her answer to both groups is: The best vegetables are the ones you actually want to eat.

“A lot of people engage in aspirational vegetable shopping” without actually using them, said Thomas, of Leesburg, Va. In that case, “It doesn’t matter how you cook them, because if they’re going in the trash, they’re not in your body.”

That said, research shows different cooking methods do affect the nutritional content of produce, but it’s not as simple as raw vs. steamed vs. roasted.

Are raw vegetables healthier than cooked?

Not always. Prolonged exposure to high heat degrades many nutrients. But cooking not only softens the cellular walls in vegetables, making them easier to digest, it also changes their structure to increase what’s called bioavailability — the body’s ability to absorb the vegetables’ nutrients, Thomas said.

The result is often more nutritious than raw food. Cooked tomatoes, for instance, release more of the cancer-fighting antioxidant lycopene than raw, she said, and cooked carrots have more betacarotene that can be absorbed. Roasting pumpkins, carrots and sweet potatoes boosts carotenoids, the rich pigments that are antioxidants known to combat inflammation in the body.

Which cooking methods are the healthiest?

Generally, the shorter the cooking time, the more nutrients are preserved. Partly because they take relatively little time, steaming and microwaving are considered the most nutritious methods (also because they require no fat to cook), said Amber Pankonin, a dietitian in Lincoln, Neb.

A close second is blanching — tossing vegetables into boiling water for a minute or two — but be careful not to leave them in the water long. Boiling vegetables, besides easily turning them to mush, runs the risk of losing water-soluble nutrients including vitamin C, B1 and folate.

“It’s leaching into the water, and you’re tossing out the water,” Thomas said. “There goes all of the nutrients that you were hoping for.”

Is there no accounting for taste?

Even dietitians say there’s no problem using a small amount of fat. Besides making vegetables more flavorful, a little cooking oil helps fat-soluble vitamins absorb in the body, said Pankonin.

That means more vitamin A from squash, carrots and sweet potatoes, more vitamin D from mushrooms, more vitamin E from bell peppers, leafy greens and asparagus and more vitamin K from greens, broccoli and onions.

For sauteing, Pankonin recommends starting over medium heat with a tablespoon of oil, though it depends on the pan. Use enough oil that the vegetables don’t stick, but not so much that it pools.

For roasting, you’ll likely need double the oil per pound of vegetables. Despite the longer cook time, roasting will still maintain some nutrients and will boost the flavor with caramelization of natural sugars.

“Flavor is king,” Pankonin said. “I would much rather see people roasting their vegetables and enjoying them, versus dealing with the mushy vegetables they’ve boiled and boiled.”

Amber Pankonin’s Sautéed Green Beans With Lemon, Garlic and Shallots

Serves: 4. Time: 20 minutes

12 oz. trimmed fresh green beans

1 tablespoon vegetable oil

1 tablespoon minced shallot

1 teaspoon minced garlic

1 tablespoon lemon juice

Kosher salt and black pepper

Blanch green beans by placing in boiling water for 1 minute, drain and place in an ice water bath. In a sauté pan, add the oil over medium high and cook the shallots for 30 to 45 seconds. Add the beans and cook for 2 to 3 minutes. Add the garlic and cook 1 to 2 minutes until the beans are tender. Season to taste with lemon juice, Kosher salt and black pepper.

Carlene Thomas’ Twice-Baked Harissa Sweet Potatoes

Serves: 6. Time: 1 hour, 10 minutes

3 large sweet potatoes

11/2 teaspoons brown sugar

1 tablespoon butter, melted

2 teaspoons harissa

Salt and pepper to taste

2 teaspoon extra-virgin olive oil

Wash potatoes and prick with a fork. In the oven preheated to 375 degrees, bake for 45 minutes, or until you can pierce with a fork. Remove and allow to cool slightly before cutting off the top third lengthwise. Scoop out the flesh using a large spoon (leave enough on the base so the skin holds its shape) and reserve bases.

In a stand mixer with whisk attachment, add the potato flesh, brown sugar, harissa, salt and pepper. Whip until fluffy. Scoop into the reserved potato skins and use a fork to create peaks.

Place potatoes on a baking sheet and brush skins with olive oil. Bake at 350 degrees for 25 minutes. Broil on high to brown if desired. Top with additional salt and harissa.