"We decided to look at these foods in combination, because we believed it was a way to learn more about real diets eaten by real people," said John Erdman, a professor of food science and nutrition, who led the study.

"Of course, it's important to analyze how specific food components influence our health, but such findings provide only the tools for further study. They should open the debate, not close it down," Erdman told a news conference sponsored by the American Institute for Cancer Research.

Tomatoes are especially hailed as protective against prostate cancer, and scientists believe the lycopene that makes them red may be responsible.

However, Erdman and colleagues found last year that lycopene supplements did little to prevent cancer in rats.

Broccoli is also believed to help prevent cancer, because it contains compounds called glucosinolates and perhaps other healthful molecules.

For the latest study, the researchers fed rats dried, powdered tomato, dried broccoli or a combination of both.

A fourth group of rats was fed finasteride, a drug shown to reduce the benign growth of the prostate and also being tested for its potential to prevent prostate cancer.

The rats were all injected with human prostate tumors. This mimics human cancer to a certain degree, although not perfectly.

The rats developed tumors, but in those given the food supplements, the tumors grew more slowly and stayed smaller than in those given finasteride, Erdman found.

The rats given both broccoli and tomato had the smallest tumors.

The study, which will be published in the December 2004 issue of the Journal of Nutrition, shows tomatoes and broccoli may act synergistically, Erdman said.

"Separately, these two foods appear to have enormous cancer-fighting potential. Together, they bring out the best in each other and maximize the cancer-fighting effect," Erdman said.