 Study subjects participate for about 3 months. During this time, there is one outpatient visit, a 4 week inpatient period, a 4 week outpatient period known as a wash out period and finally another 4 week inpatient period. During the inpatient periods The Rockefeller University Hospital becomes your home the subject must sleep here every night and consume all the food provided. During the screening visit blood and urine samples will be taken and an EKC electrocardiogram and a complete physical exam will be done. After enrollment into the study, the first 4 week inpatient period begins. You may continue to go to work or do other activities as long as you eat the diet provided and sleep at the Rockefeller University Hospital. You must eat everything that we give you and you may not substitute or supplement the diet in any way. During each 4 week stay at The Rockefeller University Hospital, there will be three flexible sigmoidoscopies done and biopsies taken of the mucosal lining of the colorectum. This procedure is painless and takes about 5 minutes. In addition, blood and stool samples will be taken every few days for follow-up and research, two 24 hour urine samples will be done on separate days during the hospitalization. Vital signs are measured every day and your weight will be measured three times per week. During the four week wash out period, the subject will return to their home, go about their normal activities and consume their normal diet. The subject will return to The Rockefeller University Hospital for the second 4 week inpatient period. The procedures and laboratory tests are the same during the second inpatient period. The study concludes with the subjects discharge from the RUH. 