"I have come to the resigned conclusion that we will not be able to persuade everybody to change their diet," Fahey said. "A pill would be better than nothing, but that doesn't mean that I'm advocating it or promoting massive pill-taking."
Just two or three ounces a day of cooked broccoli would have a protective effect, he said.
Zeisel added that people who try the pill-taking shortcut might well lose any benefit.
"It's probably a combination of ingredients in the plant that is responsible," he said. "When you try to extract them out to make a pill, it usually doesn't work."
The U.S. National Cancer Institute has information on diet and cancer.
SOURCES: Jed W. Fahey, Sc.D., faculty research assistant, Johns Hopkins School of Medicine, Baltimore; Steven H. Zeisel, M.D., director, Nutrition Research Institute, University of North Carolina, Chapel Hill, N.C.; March 6, 2009, Cancer Prevention Research