The government study found no benefit from a mega-veggies-and-fruit diet over the U.S.-recommended servings of five fruits and vegetables a day.

Researchers noted that none of the breast cancer survivors in the study lost weight on either diet. That led some experts to suggest that weight loss and exercise should be the next frontier for cancer prevention research. The study appeared in yesterday's Journal of the American Medical Association.

"It sends us back to the drawing board," said Susan Gapstur of Northwestern University's Feinberg School of Medicine. "Should we really have focused on dietary components like fruits, vegetables and fat? Or should we be focusing, in addition to diet, on lifestyle factors including physical activity and weight?"

The research was kicked off by a $5 million grant from the late Wal-Mart heir John Walton and got an additional $30 million in support from the National Cancer Institute.

Earlier research on whether a healthy diet prevents breast cancer has shown mixed results. The new study was designed to be more rigorous.

In this experiment, all the women had been successfully treated for early stage breast cancer. Their average age was 53 when the study began. A group of 1,537 women was randomly assigned to a daily diet that included five vegetable servings, three fruit servings, 16oz of vegetable juice and 30g of fiber.

The women were allowed to eat meat but were told to get no more than 15% to 20% of their calories from fat. Another 1,551 women were assigned to get educational materials about the importance of eating five servings of fruits and vegetables a day.

During the next seven years, the cancer returned in about the same proportion of women in both groups: 256 women (16.7%) of the women on the special diet and 262 women (16.9%) in the comparison group. About 10% of both groups died during that time, most of them from breast cancer.

It did not matter whether the breast cancer was the most common type -- fueled by hormones -- or not; the special diet did not prevent the cancer from coming back.

From the July 30, 2007, Prepared Foods e-Flash