The only time I had rats go off feed is when they were sick to begin with, and fortunately for me, it was most always from old age. The one time it wasn't, it was because I didn't quarantine a new male, and while he himself appeared fine, he infected my female with some respiratory illness and she was dead in 4 days. He got fed to my snake (I was very pissed off, as she was a beloved pet as well) before he could die of his illness, although he had become symptomatic.

So do these rats just eat their babies on a whim or what? I have heard of this happening in many cases before but I dont understand why they do this. Is it just that they are out of food or is it because they are old and stuff I dont get it? Does anybody have an inkling about why they do that?
There are several reasons a rat will kill/eat her babies. Poor nutrition and stress are the two main ones. The stress thing can be tricky though, because sometimes they're be perfectly fine with certain conditions, then the next time it's not ok. Or it could be a fire truck went by as she was giving birth, and she freaked and killed all of them. Another reason is that sometimes, they're just nutty. Bad genes or something. I had a couple litter killers when I first started breeding, but I fed them off right away, and never had another issue.