The lead researcher of the study, Paul Talalay, explained that "Three-day-old broccoli sprouts consistently contain 20 to 50 times the amount of chemoprotective compounds found in mature broccoli heads, and may provide a simple, dietary means of chemically reducing cancer risk."
In the study, extracts of the sprouts were fed to groups of 20 female rats for five days, and exposed them and a control group that had not received the extracts to a carcinogen, dimethylbenzanthracene. The rats that received the extracts developed fewer tumors, and those that did get tumors had smaller growths that took longer to develop.
The quest for natural sources of compounds that increase resistance to cancer-causing agents led the Hopkins group to focus on naturally occurring compounds in edible plants that mobilize specific detoxification enzymes. These enzymes (antioxidants) neutralize highly reactive, dangerous forms of cancer-causing chemicals before they can damage DNA and promote cancer.
Sulforaphane "is a very potent promoter of these enzymes," says Jed Fahey, plant physiologist and manager of the Brassica Chemoprotection Laboratory at Hopkins, and broccoli contains unusually high levels of glucoraphanin, the naturally-occurring precursor of sulforaphane. The only problem is that only sophisticated chemical analyses can reveal which broccoli plants had the highest levels of glucoraphanin, since levels vary quite a lot from plant to plant. Talalay said that "Even if that were possible, people would still have to eat unreasonably large quantities of broccoli to get any significant promotion of Phase 2 enzymes," Talalay says. The good news is that clinical studies are currently under way to see if eating a few tablespoons of the sprouts daily can supply the same degree of chemoprotection as one to two pounds of broccoli eaten weekly. The sprouts look and taste something like alfalfa sprouts, according to Talalay.
Armed with the data that research such as this provides, pharmaceutical companies are trying to develop man-made compounds that increase the resistance of cells and tissues to carcinogens. However, this will require years of clinical trials to determine safety and efficacy," Talalay notes. "For now, we may get faster and better impact by looking at dietary means of supplying that protection. Eating more fruits and vegetables has long been associated with reduced cancer risk, so it made sense for us to look at vegetables.