A recent report in the New England Journal of Medicine shows that large doses of the antioxidant vitamin pills do not prevent colon cancer. The four previous studies on how vitamin pills affect colon cancer were on small groups and were not scientifically conclusive. Several recent reports show that many vegetables contain phytochemicals that help to prevent cancer. However, it is silly to eat broccoli because it contains the anticancer chemical, sulforophan, and not include many other fruits and vegetable which also contain cancer preventing chemicals, just because many phytochemicals haven't been discovered yet. All fruits and vegetables are loaded with antioxidant vitamins and phytochemicals which prevent cancer.
Peppers contain capsaicin, citrus fruits contain coumarins.
Berries, peppers, carrots and tomatoes contain flavinoids. Tomatoes and many other fruits contain lycopenes. Garlic, onions and chives contain S-allycysteine. Licorice contains triterpenoids. Barley, wheat and flaxseed contains lignins.