Experimental studies using high-fiber supplements show that of all the fibers tested, wheat bran is the most effective in protecting against colon tumor development. The mechanisms behind this protective effect have not been elucidated completely, and the effect is most likely multifactorial. Some mechanisms, such as luminal dilution of potential carcinogens and accelerated transit through the colon, are well established. The fermentation of wheat fiber to short-chain fatty acids—especially butyric, which has been shown to inhibit tumor growth in vitro—is documented, but interpretation of the data from animal studies and clinical trials is subject to debate. Several potential mechanisms, such as effects of phytochemicals and phytates contained in wheat bran, have not yet been explored.