Antioxidant Superstars: Vegetables and Beans

Beans and a host of vegetables top the list of antioxidant-rich foods

Medically Reviewed by Brunilda Nazario, MD on September 11, 2008
5 min read

The lowly bean has been boosted to star status. A ground-breaking study that looked at numerous foods says beans -- red, black, pinto, kidney -- are high-octane sources of antioxidants.

Antioxidants are the disease-fighting compounds that Mother Nature puts in foods to help our bodies stay healthy, explains researcher Jeffrey Blumberg, PhD, professor of nutrition at Tufts University in Boston. "Our job is to take advantage of those antioxidants."

The USDA guidelines recommend eating a variety of fruits and vegetables each day, selecting from all five vegetable subgroups: dark green vegetables, legumes (beans), starchy vegetables, orange vegetables, and other vegetables. They also suggest eating at least two and a half cups of vegetables daily for people eating 2,000 calories.

Which of these are the best antioxidant foods? Researchers used advanced technology to study 100 fruits, vegetables, and other food sources to measure the levels of antioxidants. Beans were the clear winners, but so was a quirky mix of other veggies -- artichoke hearts, russet potatoes, sweet potatoes, spinach, and eggplant.

Knowing which foods have the most antioxidants is important, because in today's polluted world, the human body needs all the help it can get to fight disease-causing free radicals. That's what antioxidants do -- stop free radicals from damaging other cells in your body.

The biggest class of antioxidants is flavonoids. Researchers have identified some 5,000 different flavonoids fruits and vegetables, explains Ronald Prior, PhD, a chemist and nutritionist with the USDA's Arkansas Children's Nutrition Center in Little Rock, Ark. He authored the groundbreaking antioxidant measure study.

Yet the body simply doesn't absorb all flavonoids equally well - that is, not all are as bioavailable as others. "Bioavailability has to do with absorption or metabolism in the gut, a process we know very little about," Prior says.

Here's the science behind it: An antioxidant attached to a fiber or sugar molecule may require certain enzymes in the gut to help absorption, he explains. If those enzymes are there, the flavonoid is absorbed. Some flavonoids simply don't seem to get absorbed. It's still relatively a mystery what happens in the gut, Prior notes.

Cooking some vegetables even slightly can help boost bioavailability, Prior says. "Tomatoes are a classic example. Flavonoids in cooked tomatoes are better absorbed than raw tomatoes. We don't know for sure what's happening in the gut, but we do know this is true."

However, cooking is not always good. It kills antioxidants in some foods, he says. Until researchers figure it out, "aim to eat those at the higher end of the antioxidant chart," says Prior.

Prior's study found beans to be clear winners - one-half cup of red beans yields 13,727 antioxidants; red kidney beans have 13,259; pinto beans, 11,864; and black beans, 4,191. Beans are inexpensive and filling. Classic meals such as beans and rice, beans in a burrito, split pea soup, and a peanut butter sandwich are bean naturals. (Peanuts are not nuts; they are in the same family of plants as beans and peas.)

One-third cup of cooked beans has 80 calories, no cholesterol, lots of complex carbohydrates, and little fat. In addition, beans are full of B vitamins, potassium, and fiber, which promote digestive health and relieve constipation. Eating beans may help prevent colon cancer and reduce blood cholesterol, a leading cause of heart disease, researchers say.

Beans are also a great protein source, says Cindy Moore, MS, RD, director of nutrition therapy at The Cleveland Clinic, and spokeswoman for the American Dietetic Association. "We used to say that you needed to eat grains with beans to make it a complete protein, but we no longer think that's true," she tells WebMD. "If you get some grains sometime during the day, you'll get the benefit of complete protein."

If beans bother your digestive system, try canned beans, she adds. Also, there's Beano, an enzyme supplement that breaks down gas-producing substances in the beans. Drinking more fluids also helps, as does regular exercise. Both help your intestinal system handle the increased dietary fiber.

"To sneak beans into your diet, one really easy thing is to put them in vegetable salads," Moore says. "If you're into convenience, mix some canned beans with canned soup or with a frozen entrée. You don't have to use all the beans in the can. Just scoop out what you want, rinse them, and keep the rest in the canned juice." Frozen beans work well, too.

Among the other non-bean antioxidant stars Prior's research uncovered include:

  • Steamed artichoke hearts (7,904)
  • Baked russet potatoes (4,649)
  • Raw spinach (1,056)
  • Baked sweet potatoes (1,199)
  • Eggplant (1,039)

For a sample of what happens during cooking, note how the antioxidant levels change for some foods:

  • Raw asparagus (2,021), steamed asparagus (1,480)
  • Raw red cabbage (788), cooked red cabbage (2,350),
  • Raw yellow onions (823), cooked yellow onions (1,281)
  • Raw broccoli (700), cooked broccoli (982)
  • Raw tomatoes (552), cooked tomatoes (415)

Artichoke hearts are available in cans and jars, and are great in salads. "Some of the tastiest ones are loaded with oil, which means you get lots of fat and calories," Moore points out. "So just use a little. You don't have to have the entire jar. Think small, maybe one or two artichoke hearts, since they're so packed with antioxidants." Using canned artichokes in water or frozen, precooked artichoke hearts will help you rein in the extra calories, she adds.

To get more spinach in your diet, add chopped fresh spinach or frozen spinach to soups. Use fresh spinach in sandwiches instead of lettuce. Or make a pesto from spinach and walnuts, Moore suggests.

But don't stop with these star veggies, Moore advises. "Don't overlook all the others, with all their own special benefits. Each has its own unique nutritional footprint. Some have more fiber or different arrays of vitamins and minerals. By mixing them up, you're going to enhance what you're getting nutritionally."