Fiber-rich foods include beans, fruits, vegetables and whole wheat products. Fiber also supplies lignan which is thought to potentially reduce the risk of cancers like breast, colon, ovarian and even prostate by reducing or blocking the estrogen activity in cells. Additionally there are other phytonutrients and antioxidants found in fiber-rich foods that are associated with a reduced the risk of other diseases. High fiber-diets are still being heavily researched with regards to cancer. Studies link high fiber diets to decreasing cancer risk in a number of different ways. By forming heavier and bulkier stools, fiber reduces the time it takes to pass waste through the digestive tract, decreasing the concentration of potential carcinogens. Insoluble fibers also keep the pH level of the intestinal tract in a healthy balance that decreases the ability of microbes to produce carcinogens.