If you are worried about constipation from the MRE's, or any other source, a bottle of mineral oil in your gear will fix that. A good glug every day or so will fix you right up. You can even use it for other needs, like oiling stuff. Not the greatest taste in the world (it tastes like, well, oil), but it works. It will take a few days to start working if you are really plugged up, so don't go nuts drinking it, or you will be sorry. Verrrrry sorry. Don't ask me how I know this...