Several carrots

First of all, here’s the most important point: Eating vegetables in any form is something people should be doing more of. Whether they’re raw or cooked, veggies supply important nutrients for very few calories—so if you love raw carrot sticks, don’t hesitate.

That said, cooked vegetables can sometimes be a slightly more nutritious option (which is good to know as the weather cools down and salad grows less appealing). “Common wisdom says cooked vegetables have fewer nutrients than fresh ones, but that isn’t always the case,” says Amy Keating, a dietitian at CR. “Some nutrients in fruits and vegetables are bound in the cell walls. Cooking breaks those walls down, releasing the nutrients so your body can absorb them more easily.”

Below are seven vegetables you may want to heat before eating to unleash their full potential in terms of nutrition and taste—plus one vegetable you should always cook for safety’s sake.

Spinach

The leafy green is packed with nutrients, but you’ll absorb more calcium and iron if you eat it cooked. The reason: Spinach is loaded with oxalic acid, which blocks the absorption of iron and calcium but breaks down under high temperatures.

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A study found that cooking spinach quickly in boiling water, then plunging it into cold water, reduced oxalate content by 40 percent, on average, which was more effective than pan or pressure cooking.

Try this: Blanch a bunch of fresh spinach leaves in boiling water for 1 minute, then plunge in ice water for a few more. Drain well and keep wrapped in the fridge. This makes it easy to add a serving of vegetables to omelets, soup, and other dishes. Cooked spinach should keep a few days. 

Mushrooms

A cup of cooked white mushrooms has about twice as much muscle-building potassium, heart-healthy niacin, immune-boosting zinc, and bone-strengthening magnesium as a cup of raw ones. That’s according to the Department of Agriculture’s nutrient database. Even mushrooms considered edible can sometimes contain small amounts of toxins, but they can be destroyed through cooking.

Try this: Mushrooms are like sponges when it comes to soaking up fat, so go easy on the oil. Because they release a lot of water when cooking, don’t overcrowd the pan, and let them cook down. For a flavor boost, try sautéing mushrooms with garlic and sprigs of fresh thyme. Serve as a side dish alone or mixed into cooked whole grains, or use them as a burger topping.

Carrots

Cooking ignites this veggie’s cancer-fighting carotenoids, the nutrient responsible for its orange hue. A 2008 study in the Journal of Agricultural and Food Chemistry found that boiling carrots until tender boosted their concentration of carotenoids by 14 percent. But hold the fry pan! Pan frying caused carotenoid levels to dip by 13 percent.

Try this: To maximize the nutritional benefits, boil carrots whole before slicing. Cooking them that way keeps valuable nutrients from escaping into the cooking water. Added bonus: Once cooked, they’ll be easier to cut. Top with a tiny bit of honey or maple syrup to bring out the natural sweetness of carrots.

Asparagus

A study in the International Journal of Food Science & Technology found that cooking these stalks raised the level of six nutrients, including cancer-fighting antioxidants, by more than 16 percent. Another study in the International Journal of Molecular Sciences found that cooking asparagus more than doubled the level of two types of phenolic acid, which some studies have linked to lower cancer rates.

Try this: To keep spears crisp and help them to retain nutrients, dunk them whole into a pot of boiling water. Watch carefully and remove them with tongs as soon as they turn bright green. Toss with lemon juice and olive oil; a little fat helps your body absorb the antioxidants in asparagus and other vegetables.

Tomatoes

With tomatoes, whether they’re baked, fried, or even puréed into spaghetti sauce, heat increases a phytochemical, lycopene, that has been linked to lower rates of cancer and heart disease. It also gives red tomatoes their rosy color. According to a 2002 landmark study, heating tomatoes for 30 minutes at 190.4° F (the temperature of soup simmering on a stove) boosted the levels of absorbable lycopene by 35 percent. Though cooking reduced the vitamin C content, the study found that it raised the total power of the disease-fighting antioxidant by 62 percent.

Try this: Instead of serving raw tomatoes cut up in a salad, try roasting them in the oven. Roasting concentrates their flavor, Keating says. Arrange quartered tomatoes on a sheet pan in one layer, drizzle them with olive oil and balsamic vinegar, sprinkle with garlic, salt, and pepper, then bake for about a half-hour at 200° F. You can use them as a side dish, on sandwiches, or tossed in salads.

Red Bell Peppers

Bell (or sweet) peppers are packed with nutrients, but the red variety stands out. Ounce for ounce, they have six times as much vitamin C as citrus fruit. Plus they’re a great source of antioxidants, especially the carotenoids beta carotene, beta-cryptoxanthin, and lutein, which are important for cell communication, eye health, and many other functions.

You do lose some vitamin C when you cook red bell peppers, especially when the vegetable is boiled or steamed, because the vitamin can leach out into water. But heat breaks down the cell walls, which makes the carotenoids easier for your body to absorb.

Try this: To get the most out of your red bell, consider a recipe that involves lightly roasting or stir-frying it. According to a Korean study from 2012, those methods are good if you’re trying to maximize the veggie’s nutritional value. Roast green beans and a sliced red pepper in a little olive oil and vinegar, for example, or toss some slivers into a stir-fry. And cooking 10 minutes or less generally gets you the most benefits.

Broccoli and Cauliflower

When raw, these crucifers, as their class is called, are packed with glucosinolates, which can convert to variety of cancer-fighting compounds in your body. In order for the glucosinolates you eat to make that transition, however, an enzyme in the veggies called myrosinase has to be active. You can activate it by chopping the veggies up or chewing as you eat—but cooking can destroy it.

Why, then, do broccoli and cauliflower make this list of vegetables better eaten cooked? Because while you’d be in good shape glucosinolate-wise if you ate them raw, these vegetables also contain the fibers raffinose and cellulose, which can, for many people, cause bloating, gas, and other problems. Cooking can make these vegetables easier on your digestive system.

Fortunately, science has discovered a way out of this conundrum. A 2012 study published in the Journal of Agricultural and Food Chemistry found that steaming the veggies preserves myrosinase and therefore the cancer-fighting compounds you can get from them (plus other research has found that steaming also preserves these crucifers’ vitamin C).

What’s more, a 2018 study from the same journal found that chopping broccoli and letting it sit for 90 minutes before you cook it also allows myrosinase to activate. When the vegetables were subsequently stir-fried, the researchers found, they did contain the cancer-fighting compounds. (Others have suggested that a wait time of as little as 40 minutes may also have a significant positive effect.)

Try this: You’re probably almost always going to chop cauliflower and broccoli up before cooking them, but do let them sit for a bit before you heat them. They’re delicious steamed or roasted: You can top them with a light sauce, a dash of Parmesan cheese, or just a little lemon and garlic or fresh herbs for added flavor. And of course, per the research, they’re also good in a stir-fry. 

Sprouts (Alfalfa, Bean, Mung Bean, Etc.)

Finally, there’s one nutritious veggie that it’s just not a good idea to eat raw for safety reasons. Sprouts are, essentially, baby plants—seeds that have been germinated in warm, watery conditions.

But their production may account in part for why raw sprouts are often contaminated with bacteria that cause foodborne illness, such as listeria and E. coli. According to the Food and Drug Administration: “Sprouts represent a special food safety concern because the conditions under which sprouts are produced (time, temperature, water activity, pH and available nutrients) are also ideal for the growth of pathogens, if present.” And according to the FDA, between January 1996 and August 2018, there have been 50 outbreaks of foodborne illnesses associated with contaminated sprouts.   

Try this: The Centers for Disease Control and Prevention advises that sprouts shouldn’t be consumed uncooked. People who are pregnant, are very young or very old, or have a compromised immune system should be especially careful because they’re more likely to get sick from foodborne bacteria and have a worse outcome.

In restaurants, request that raw sprouts be left off your dish (salads are often topped with alfalfa sprouts, for instance). At home, you can oven roast them (it doesn’t take long) or boil briefly till they’re heated through and tender-crisp and then use in salads. Or just add them directly into your stir-fries or soups while they’re cooking. 

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