Lifehacker about why we crave, how it may have come about and techniques that could help up to combat cravings.
A small snippet for those not interested enough to read the whole thing.
"Take a food you have a false promise of reward with (potato chips, a box of Girl Scout cookies, whatever). Eat as much as you can and notice how you go from being happy to feeling stuffed or sick afterwards. Pay attention to every emotion you go through. Notice how the taste of the food changes as you move through the bag. The goal is to show you that even after you eat an entire bag, you're not satisfied. But when you're stuffed and feeling gross, your brain is still telling you to crave the food you just ate. The goal of the exercise is to rewire your memory and tie the craving with the consequence, not the reward."