The present invention provides food or preventive drugs whereby food residues retained in the digestive tract over a long period of time due to, for example, overeating even in a healthy person not suffering from constipation and having regular defecation can be discharged by elevating the transit speed without showing cathartic effects or unpleasant symptoms, thereby protecting the human body from the undesirable effects of putrefactive and toxic metabolites and enabling health enhancement and the prevention of colon cancer. Namely, use of one or more members selected from among indigestible saccharides, low-viscosity and water-soluble dietary fibers and magnesium compounds in an adequate amount makes it possible to shorten maximum transit time through the digestive tract and prevent colon cancer without causing any cathartic effect, loose stools or unpleasant side effects. Moreover, transit time through the digestive tract can be shortened by using adequate amounts of lactulose and magnesium oxide without causing any cathartic effect, loose stools or unpleasant side effects.