@thox: when I first started for the Forest Service, as a volunteer on a wilderness trail crew we had a huge cache of mountain house #10 cans. That was dinner five days a week. Breakfast was either dehydrated eggs (w/w/o bacon bits, definitely prefered with!), bisquik biskets, or pancakes. Lunch was usually trail mix, smashed pb&j sandwiches, or candy bars (I was 19 and knew nothing of nutrition).
For the first third of the summer it was fine, but I was frequently packed up five days a week, which was convienient in the backcountry, albeit uncomfortable. About mid-summer I got giardia and frankly, mountain house saved my arse, literally. While giardia sucked, I didn't have health insurance and couldn't afford the meds to clear it up, so the giardia stayed with me for almost two years, with lapses of better and worse. For those two years, I never traveled anywhere without my own roll of TP with me.
Anyway, with the right variety and some other stuff to eat one or two meals a day, its not bad, but do buy some exlax. I've also baked my own 100% whole wheat bread and had similar issues, despite the fact that all that fiber should do the opposite. Any major diet change causes problems, so integrating some of your preps into your daily diet is definitely a good idea.