Phytochemicals are believed to have many health benefits. Indoles, which may interfere with estrogen metabolism and therefore could reduce risk for some estrogen-related cancers such as breast cancer. They are also found in cruciferous vegetables. Isoflavones , which are found in soy foods and have a number of effects that may affect cancer risk. Lignans, which are found in rye and flax seed and may reduce breast cancer risk because they act as anti-estrogens.
Flavonoids are a special class of phytochemicals that includes hundreds of different compounds.
Most are excellent antioxidants and some have hormonal properties. Among some of the most studied flavonoids are quercetin , which is found in tomatoes, potatoes, broccoli, and onions and kaempferol, which is found in kale and endive. Beta-carotene from foods has been linked to a reduced risk for lung cancer. Lycopene , found in tomatoes and strongly linked to reduced risk for prostate cancer. Lutein , found in leafy green vegetables and linked to reduced risk for cancer and macular degeneration .