The water and fiber make fecal matter bulkier, so carcinogens are diluted. Fiber may bind with these bile acids and evict them from the intestines. Also, bacteria in the colon ferment the fiber creating a more acidic environment which may make bile acids less toxic. Fiber is also protective against other forms of cancer. Studies have shown that stomach cancer and breast cancer are less common on high-fiber diets.
Fiber affects levels of estrogens in the body.
Estrogens are normally secreted into the intestine, where the fiber binds with the hormone and moves it out of the body. 4 Without adequate fiber, the estrogen can be reabsorbed from the intestine into the bloodstream. High levels of estrogen are linked to a higher risk of breast cancer. In the U.S., the average daily fiber intake is 10 to 20 grams per day. Experts recommend 30 to 40 grams per day.