The Health Professionals Follow-Up Study tracked a class of men from 1986 to 1995. In 1986, the men were from 40 to 75 years old. Over that eight-year period, 204 men had an ischemic stroke.

The Nurses' Health Study followed a group of female nurses from 1980 to 1994. In 1980, the women ranged in age from 34 to 59. A total of 366 women had an ischemic stroke during that 14-year period.

Researchers sought to identify other causes of stroke risk, including smoking, lack of exercise and family history, and focus instead on strokes not obviously attributable to these factors.

Walter C. Willett, a co-author of the HSPH study, says no one nutritional component of produce is responsible for lower health risks.

"There are many chemicals in fruits and vegetables that plausibly reduce the risk of stroke," he says. "We're probably seeing contributions of a number of nutrients in these foods."

Previous health studies have shown that the nutritional parts of fruits and vegetables--like fiber, antioxidants and potassium--have been associated with a reduced risk of cardiovascular disease.

And nutritional guidelines emphasizing a diet rich in fruits and vegetables, like the food pyramid, have been around for years.