There’s a reason pizza rat fought long and hard to carry that massive slice up a flight of stairs or why the Teenage Mutant Ninja Turtles considered it their main source of food despite their biological inclination toward plants and fish.
The New York Daily News reports that researchers at the University of Michigan examined why people became hooked on certain foods more than others and found that cheese (one of pizza's main ingredients) is as addictive as drugs. That’s because of a chemical called casein, which is present in dairy products, "breaks apart during digestion to release a whole host of opiates called casomorphins." At least, that’s what Dr. Neal Barnard of the Physicians Committee for Responsible Medicine says.
Registered dietitian Cameron Wells added that casomorphins “really play with the dopamine receptors and trigger that addictive element." That’s pretty much how drugs work, too.
The study, published in the U.S. National Library of Medicine, also determined that the more processed and fatty the food was, the greater chance of it being addictive.