Undigested Meat in Colon?

[GalateaDancer]

I had someone whip out this factoid on another board I frequent:

"the average colon contains around 5 pounds of undigested meat at any one time"

I googled, and found similar claims, but they all seemed to be on woo-woo holistic health sites, with no medical study citation. Anyone know where this claim comes from, and if it has any true medical/boilogical basis?