Scientists are only now beginning to understand the role of chemical ions called free radicals circulating in the body. They are a by-product of the body's normal chemical activity. Free radicals have an extra electron, and this electrical charge makes them want to attach to something. Usually, they end up binding with cell membranes, or parts of cells, thus damaging them. Researchers say that ages the cell.

Dr. Jim Joseph from the US Department of Agriculture lab in Massachusetts says antioxidant chemicals can prevent that damage.

"Your body makes a certain amount of antioxidant and these are normally able to protect the cell," Joseph explains. " Now what happens though, if a hit gets through, is you need something to clean things up. You need something to fix it."

Joseph says damaged DNA can be repaired, in fact "this is what antioxidants do whenever free radicals impinge on them."

Joseph and his colleagues at the USDA lab studied aging rats that were fed a regular diet. They compared them to rats that ate food high in antioxidants. Then the scientists put the rodents through a series of tests that measured their brain capability. "We found? that they were able to perform much better on these tasks, on these motor and cognitive tasks, than the animals who didn't get the diet," he says.

Joseph says the antioxidants in the smart rats' diets came from a variety of fruits and vegetables, such as blueberries, strawberries, spinach, blackberries, cranberries, walnuts, avocados, and pomegranates.

"The one characteristic you'll note that all of these have is the colors," Joseph says. "So if you need a guide, go by the dark intense colors. But don't forget white, because garlic and cauliflower are also high in antioxidants, they're just a little different variety."

Joseph says people, like rats, lose cognitive ability as they age. He says these same benefits of antioxidants in fruits and vegetables could be translated to humans.

"We didn't make them young again, but we made them better," says Joseph with a laugh. "We're not working miracles here we're just helping out a little bit.

Joseph's research is published in the journal, Neurobiology of Aging. You can also read about the research online in the U.S. Department of Agriculture's magazine, Agricultural Research.