By Charlotte Libov
Medically reviewed by Farrokh Sohrabi, M.D.

Vegetables are important weapons in the fight against heart disease, cancer, and a host of other ailments like stroke, vision problems, and hypertension. That's why the U.S. Department of Agriculture says they should make up more than one-quarter of the foods we put on our plates each day -- with many nutrition experts recommending even more veggies.

But depending on how vegetables are eaten, the valuable vitamins, phytochemicals and flavonoids they possess can be either enhanced or destroyed.

More from Everyday Health:
Lady Gaga Launches Shame-Free 'Body Revolution'
Virus Could Fend Off Pimples
Active Video Games Burn Calories

“When you're preparing vegetables, you have to be careful in how you cook them because the reality is that heat always destroys some of the nutrients,” says Sue Gebo, R.D., M.P.H., a West Hartford, Conn., dietitian and assistant professor at the University of Connecticut School of Medicine. "But on the other hand, the nutrients in some vegetables are better absorbed after some cooking.”

Raw-food aficionados may think that cooking destroys the nutrition in all vegetables, but this isn't true. When it comes to tomatoes, for instance, cooking them actually enhances their healthful properties because heat breaks down the thick cell walls of this fruit -- OK, it's not technically a veggie, but we treat it like one -- which better releases its nutrients.

Although there are exceptions, griddle and microwave cooking generally help maintain the highest levels of antioxidants, while pressure-cooking and boiling lead to the greatest losses. The advantage of microwaving doesn’t surprise Gebo, who notes that this process cooks food lightly, just as steaming does.

The problem is that no single cooking method is best for optimal nutrition. With that in mind, here's a guide to bringing out the healthy best in the best-for-you veggies. What's your favorite way to eat your veggies? Share in the comments below.

Loading Slideshow...
  • Asparagus

    Asparagus is high in antioxidants, folate, and potassium. But because folate is very sensitive to heat, lightly steaming the stalks is best.

  • Artichokes

    Heat doesn’t seem to bother these perennial thistles, which are high in both heart-healthy fiber and antioxidants, so cook them any way you like.

  • Broccoli

    This disease-fighting cruciferous vegetable is very sensitive to heat, so steam or microwave it to retain broccoli’s nutritional benefit. If you cook it too long, you destroy the enzymes that break down glucosinolates into cancer-fighting agents. This means that though cream of broccoli soup may taste good, it doesn’t provide the same nutrients as a cup of lightly steamed broccoli.

  • Carrots

    Carrots are high in beta-carotene, which the body converts into vitamin A, but they're also high in folic acid, which is very sensitive to heat exposure. Eating carrots raw is fine, but their nutrients are actually better absorbed after very light cooking.

  • Green Beans

    Green beans have been found to keep their antioxidant levels after most cooking methods, so feel free to steam, boil, or microwave.

  • Spinach

    Spinach, along with other leafy greens, is rich in potassium and high in folic acid. It loses 64 percent of its vitamin C after cooking, so some say it's best to enjoy spinach raw in a salad. However, some studies suggest that <a href="http://www.scientificamerican.com/article.cfm?id=raw-veggies-are-healthier">cooking spinach</a>, and other vegetables that supply antioxidants, boosts the available supply of the helpful compounds. <em><strong>CORRECTION:</strong> A previous version of this slide stated that spinach was always best consumed raw.</em>

  • Tomatoes

    Tomatoes are packed with antioxidant, including lycopene — a potent protector against many types of cancer. Cooking is actually beneficial to tomatoes, which means the body absorbs more lycopene from tomato sauce, for example, than from raw tomatoes. If you are enjoying them raw, sprinkle them with olive oil, as this combo is a particularly effective way to promote lycopene absorption.

For more on diet and nutrition, click here.