I thought the same after reading all the sites about colonics and colon cleansing supplements. It actually took one routine colonoscopy and a small bottle of Phosfo Soda to get my colon so clean in 12 hours, that plain water was coming out without changing color, sorry for the gross details. They wanted my colon to be so clean that they could clearly see, and it worked. There is not much in our colon and especially those "cement like materials" like some colon "gurus" claim just to make you get the procedure done or or buy the supplement, which are mostly based on herbal laxatives like senna. Funny, but after the procedure I become "too regular", I think due to a good bacteria flushed out. Then it went back to normal. Constipation could be a sign of slugish liver, IBS, hypothyroid, not enough fat, too much or too little fiber, etc. What works for me is enough of good fats, live culture yougurt, and some bran crackers, which are also low carb. Phyllium and flax meal did not work for me either, especially in large quantities.