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.
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.
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.
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.
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.
Flavonoids in cooked tomatoes are better absorbed than raw tomatoes.
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.