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I'm sorry I couldn't get back sooner, but I've been a bit busy. Thank you all for your varied replies. I have looked at poop.com, very interesting. Also, interesting about the colostomy bag. I was, actually, just curious, I fully realise [Lil O'lady] that the body gets food from what is put in. I suppose I should have asked "can the level of waste be controlled". I was, myself, thinking of the astronauts as Richard1966 pointed out. I am also a vegetarian, and am very aware about skins, pips, seeds etc. being just waste but acting as fibre. But do really need fibre? And what ethrandron said is particularly interesting. And thank you joko, you saved me having to say it. Hooray for Answerbank.