A previous study showed that men who ate two or more servings of broccoli per week had a 44% lower risk of bladder cancer than those who ate less than one serving a week.

Now researchers say they may have found at least one ingredient in the cruciferous vegetable responsible for this beneficial effect, and it's only released after chopping, chewing, or digesting broccoli.

"We're starting to look at which compounds in broccoli could inhibit or decrease the growth of cancerous cells," says researcher Steven Schwartz, professor of food science and technology at Ohio State University, in a news release. "Knowing that could help us create functional foods that benefit health beyond providing just basic nutrition."

Broccoli's Cancer-Fighting Chemicals

First, researchers isolated a group of chemicals called glucosinolates, which are found naturally in crunchy, cruciferous vegetables. These chemicals are converted into compounds known as isothiocyanates during chopping, chewing, and digestion.

Then they tested the ability of both chemicals to stop the growth of bladder cancer cells in the lab.

The results showed that the group of chemicals derived from chopping, chewing, and digesting broccoli (the isothiocyanates) halted the growth of even the most powerful form of bladder cancer cells. But glucosinolates, from which isothiocyanates are derived, had no effect.

"There's no reason to believe that this is the only compound in broccoli that has an anti-cancer effect," says researcher Steven Clinton, associate professor of hematology and oncology at Ohio State University, in the release. "There are at least a dozen interesting compounds in the vegetable."

"We're now studying more of those compounds to determine if they work together or independently, and what kind of effects they have on cancer cells," says Clinton.

Researchers presented the results of the study at a recent conference of the Institute of Food Technologists.

They say young broccoli sprouts naturally contain higher levels of these chemicals than full-grown broccoli spears. But eating the spears still appears to provide health benefits.

It's too early to say just how much broccoli or broccoli sprouts a person needs to eat to prevent or slow down the progression of bladder cancer. Other cruciferous vegetables, such as cabbage, brussels sprouts, and cauliflower, may also contain similar cancer-fighting chemicals.