Any science behind bowel cleansing?

I am new to this forum and have seen a number of messages about cleansing. I would appreciate someone directing me to some good Science which indicates that a lot of old, rotting fecal matter accumlulates in the bowel and needs to be removed. My understanding that is that when people go in for routine colonoscopies, everything is pink--no rotting, 10-year-old cornflakes hiding about and causing disease. If there Science behind colon cleansing or just anecdotes?




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