Low-Fiber Diet or High-Fiber Diet in Preventing Bowel Side Effects in Patients Undergoing Radiation Therapy for Gynecological Cancer, Bladder Cancer, Colorectal Cancer, or Anal Cancer

RATIONALE: Fiber may lessen bowel side effects caused by radiation therapy. It is not yet known whether a high-fiber diet is more effective than a low-fiber diet in preventing bowel side effects caused by radiation therapy.
PURPOSE: This randomized clinical trial is studying a high-fiber diet to see how well it works compared with a low-fiber diet in preventing bowel side effects in patients undergoing radiation therapy for gynecological cancer, bladder cancer, colorectal cancer, or anal cancer.