Holy Crap! The formula for how much poop to what you eat

Faeces weight = Wf(1 + Hf) + Wb (1 + Hb) + Wm(1 + Hm)

where Wf, Wb and Wm are respectively the dry weights of fibre remaining after fermentation in the colon, bacteria present in the faeces and osmotically active metabolites and other substances in the colon which could reduce the amount of free water absorbed, and Hf, Hb and Hm denote their respective water-holding capacities.

You know, 19-280 grams per day per Briton is a big margin.