A quote from this LA Times article, Cheese really is crack. Study reveals cheese is as addictive as drugs:
Cheese happens to be especially addictive because of an ingredient called casein, a protein found in all milk products. During digestion, casein releases opiates called casomorphins; "[Casomorphins] really play with the dopamine receptors and trigger that addictive element,"
The study found certain foods are addictive because of the way they are processed. The more processed and fatty the food, the more it was associated with addictive eating behaviors.