There's nothing more nutritious than a heaping salad of colorful raw vegetables, right? Not so fast, says new research. Scientists are finding that various methods of cooking veggies—from boiling carrots to steaming broccoli—can actually boost certain nutrients. "Some of the healthiest plant pigments in vegetables are released only when they're cooked," says Elizabeth Johnson, Ph.D., a scientist at the Friedman School of Nutrition Science and Policy at Tufts University. "You get more carotenoids, for example, from steamed spinach than from a spinach salad."
Raw veggies are still a great way to get vitamins and minerals, but specific cooking tips can release additional nutrients—or preserve the health benefits while making the food tastier. Next time you assemble a hearty salad or a crudites platter, toss in some of these steamed, boiled, baked, or roasted additions.
Broccoli: steam
Raw: Broccoli is high in potential cancer-fighting nutrients such as betacarotene, lutein, and flavonols.
Cooked: Steamed broccoli has higher concentrations of many carotenoids (including beta-carotene and lutein) than raw, according to a recent study in the Journal of Agricultural and Food Chemistry. Plus, it retains nearly 70 percent of its vitamin C and virtually all of its kaempferol, a cell-saving flavonoid.
Bonus: To maximize the nutrients you get from your broccoli, wait to wash and cut it until just before steaming, suggests Ellie Krieger, R.D., author of So Easy and host of Healthy Appetite on the Food Network. Washing and cutting speeds up deterioration.
Carrots: Boil until tender
Raw: Carrots are a good source of vitamin C and carotenoids, a family of antioxidants that includes beta-carotene. These contribute to good eye health and may also reduce your risk of heart attack and some forms of cancer.
Cooked: Boiling makes the carotenoids 14 percent more concentrated, according to a recent study in the Journal of Agricultural and Food Chemistry. Dietary fiber in the cell walls of carrots traps the carotenoids, but high heat releases and concentrates the compounds, making it easier for your digestive tract to access them, explains Philipp Simon, Ph.D., a scientist with the USDA Vegetable Crops Research Unit. The study also found that boiling increases carrots' total antioxidant capacity (their ability to attack free radicals) while only slightly diminishing vitamin C levels.
Bonus: Add a drop of oil to your cooked carrots; the fat helps your body absorb more of the beta-carotene.
Garlic: roast cloves for no more than 3 minutes
Raw: Garlic contains alliinase, an enzyme with antiplatelet properties that may help reduce blood pressure and prevent blood from clotting, which decreases your risk of heart disease.
Cooked: Roasting garlic cloves (for up to 3 minutes at no more than 390°F) helps retain nearly all of their anti-platelet capabilities—with less of the odoriferous side effects of raw, say researchers at the USDA and the National University of Cuyo in Argentina. Turn off the heat after 3 minutes—by 6 minutes, garlic loses about 80 percent of its clot-busting abilities; by 10 minutes, 100 percent. And don't cook in the microwave; it destroys the alliinase, says Simon.
Bonus: Crush or chop cloves before cooking to release even more alliinase, even as cooking times increase.
Root Vegetables: roast with skins on
Raw: Winter veggies such as potatoes, turnips, and parsnips are high in fiber and vitamins, but many are not commonly eaten raw.
Cooked: Roasting with skins intact helps retain all the nutrients. If you prefer boiling, leave the skins on (peel them after cooling, if necessary), and boil them in large chunks (preferably whole) to preserve the veggies' water soluble nutrients, says Krieger.
Bonus: Choose a colorful variety for added health benefits. Several studies show that root vegetables with darker skins (red potatoes) or flesh (purple sweet potatoes) have more cancer fighting polyphenols than their lighter colored cousins.
Brussels sprouts: steam or stir-fry
Raw: Brussels sprouts contain sulforaphane, a powerful phytochemical that helps protect against breast cancer.
Cooked: Steaming or stir-frying as quickly as possible preserves more of the cancer-fighting compounds. (Boiling Brussels sprouts causes sulforaphane to leach into the water, according to research.)
Bonus: The tough cores will cook faster and more evenly if you cut an X into the bottom of each stem.
Tomatoes: roast with olive oil
Raw: Tomatoes are rich in lycopene, a carotenoid that gives this fruit its red hue. Lycopene is also a powerful antioxidant that can reduce the risk of certain cancers and heart disease.
Cooked: Roasting tomatoes causes cell walls to burst, releasing more lycopene. A recent German study published in the British Journal of Nutrition found that 77 percent of 198 people following a strict raw food diet had plasma lycopene levels below what's considered optimal.
Bonus: Splash cherry tomatoes with olive oil, then roast them in the oven until their skins rupture, suggests Krieger. Lycopene is fat soluble, so adding olive oil helps your body absorb it.
Asparagus: steam vertically
Raw: One cup of asparagus contains nearly 20 percent of the recommended daily intake of folate, a B vitamin that helps protect your cardiovascular and nervous systems. Recent studies link a diet high in folate with a decreased risk of Alzheimer's, stroke, and heart disease. Since folate is water soluble and sensitive to heat, cooking can diminish it.
Cooked: Steaming gently in a vertical steamer keeps the fragile tips—which contain most of the water-soluble nutrients—away from the liquid. (You can also steam them in a regular pot and keep the tips out of the water.) This imparts more flavor while retaining all the benefits of raw.
Bonus: Store asparagus in a cool, dark space (the back of your produce drawer,
Beets: steam gently
Raw: Beets are high in betanin, a powerful plant pigment and antioxidant that can halt free-radical damage and may even stop the growth of tumor cells in the stomach, colon, lungs, and nervous system, according to several studies.
Cooked: Lightly steam beets to retain more cancer-fighting powers, Johnson says. Betanin is highly sensitive to heat, so intense cooking methods like boiling or roasting destroy the benefits.
Bonus: Peel and chop the beets before steaming to help liberate the betanin from the tough cell walls and allow the beets to cook faster.
Onions: bake for 5 minutes in foil
Raw: Onions are one of the best sources of quercetin, a flavonoid with anti-inflammatory powers that may help control allergies and asthma, as well as help treat Alzheimer's and Parkinson's diseases.
Cooked: Baking thick chunks wrapped in foil for 5 minutes at 390°F preserves 99.5 percent of the quercetin compounds while diminishing the bite and odor, says a 2008 USDA/National Food Research Institute study.
