Actually, you may not be too far from the truth. Evolutionary Psychology tells us that when we were in the ancestral environment, we carried a natural craving for fat over fiber - because we had to work to get fat, whereas fiber was everywhere. Our brains haven't changed too much, quite like the rest of our body, and that holds true today. However, now fat is absolutely everywhere - and we still crave it just as much as before. All fast food chains unwittingly (or maybe not so unwittingly) cash in on this. It is innate within us.

So maybe eating disorders are some minds revolting against the recent (recent in terms of the big picture) en masse availibility of fat...?