Broccoli is considered as the number one anti-cancer food by the National Cancer Institute. It contains sulforaphane which stimulates the body's production of substances known as Phase II detoxification enzymes. The Phase II detoxification enzymes destroy carcinogens and free radicals before they attack healthy cells. Other sources of sulforaphane are kale, cabbage, cauliflower, bok choy, brussels sprouts and mustard or turnip greens.