Acts as an antioxidant, and may protect against most forms of cancer, leukemia, glioblastoma multiforme, and bladder cancer. Soy's soluble fiber reduces the risk of many digestive system  cancers, such as colon cancer and rectal cancer. The water-absorbing fiber may dilute intestinal carcinogens and  usher them out of the body, as well as spur growth of bifidobacteria, the good bacteria that helps prevent colon cancer.