I can't answer for LL, but when I did CD last year definately! I don't know if in the end it was the foodpacks or just some virus or, probably both + a little lack of willpower.... but at the time I had no energy, kept passing out then got quite ill after passing out in the snow (though luckily was with people!)
Like I said, I don't know what part CD played in it, but imo right then my body needed more than it was getting... and if it gets to that point again i'll go straight to rtm and either take a break or do more conventional methods.
Unless your asking if although you can survive on foodpacks you feel nauseous at the thought of having to actually have another one.... felt that too! x