Psyllium husks
I have it many mornings stirred into my protein drink. I love it. it is not like your typical Milk of Magnesia effect - it kind of improves texture of stools so that they pass thru efficiently.
I also like to use it on too hungry days - put a tablespoon in a glass of warm water and it fills me up temporarily.
I get it out of bulk bins at the healthfood store - best price.