Maybe this has been asked/answered before, but I couldn't find anything after a quick search.
Let's assume what we're eating is actually "fresh" as far as rations go. And when I say fresh I don't mean "fresh" by Steve 1989 standards, but actually within best-before dates, ration was stored properly, etc.
I recall reading something about Spanish rations not being recommended for consumption for more than 30 consecutive days and I'm sure there are other guidelines for other nations.
So the question is of course "why? and what if?", so that's 2 questions actually, but related

I assume there's a bucket-load of preservatives and other weird stuff in all the rations which makes them bad to live off of.
Sure, you might need nutritional supplements as well and a varying diet is always good to play it safe, but I can't imagine that's the only reason you shouldn't keep eating nothing but rations for extended periods.
I'm not sure this is the right place to ask, seeing as we're all happily munching down rations, but also I assume some of you are well informed about the actual health hazards that come with it.
Like... Assuming the rations are good, you don't get tired of them and you don't exceed the daily recommended calory intake etc, would you have a ration every day (or feed this to your kid) every day? If not, why?
Is there any info about it somewhere?