The varieties of broccoli typically sold in supermarkets do not vary that much, but they do differ. Other fruits and vegetables including tomatoes, garlic and carrots also contain varying amounts of cancer-fighting chemicals. The hotter the weather, the more lycopene tomatoes produce. Processing increases lycopene levels. The National Cancer Institute recommends eating at least five servings of fruits and vegetables daily.
Studies suggest that people who eat broccoli have a lower incidence of colon and rectal cancer.
Sulforaphane, a product of the glucoraphanin in broccoli, induces production of enzymes that can deactivate free radicals and carcinogens. The enzymes have been shown to inhibit tumors in laboratory animals. The Agriculture Department research, published in January in the Journal of the American Society for Horticultural Science, identified high-glucoraphanin strains of broccoli that could be used in producing new hybrids. Scientists face several challenges. For one, it is not known how much of the various phytochemicals people need or whether too much could be harmful.