This study recently came out finding that the development of obesity in rats (by eating a diet of high sugar and fat) led to the same changes in the brain as in cocaine or heroin addiction.
Obese rats (but not lean rats) developed compulsive-like feeding behavior and the down-regulation of dopamine receptors. The rats were unconcerned about any negative consequences from their food consumption… even painful stimuli (electric shocks to their feet) did not stop them from eating!
Researcher Paul Kenney said, "People know intuitively that there's more to [overeating] than just will power… there's a system in the brain that's been turned on or overactivated, and that's driving it at some subconscious level."
Another scientist, Dr. Gene-Jack Wang, describes the food we eat as similar to cocaine: "We make our food very similar to cocaine now. We purify our food. Our ancestors ate whole grains, but we're eating white bread. American Indians ate corn; we eat corn syrup."