Most of us have, at one point in our lives, experienced intense cravings for unhealthy foods. Whether it be for chocolate, donuts, salty snacks or refined carbs, our bodies appear to want them -- and we're often all too happy to submit. There's just one problem: Eating these foods doesn't seem to end the cravings. What is going on here? Are our bodies playing a cruel joke on us? Well, not quite.