Cruciferous vegetables comprise a class of vegetables which includes broccoli, Brussels sprout, cabbage, cauliflower, kale and turnips. Cruciferous vegetables contain indoles.
Epidemiolgical studies have shown people who frequently consume cruciferous vegetables have a reduced risk of stomach cancer and colon cancer.
Disorga, C. & L. Groll. 1981. Nutrition and Cancer Prevention: A Guide to Food Choices. Northern Calif Cancer Program, Palo Alto. 25.