Ever noticed that eating Cool Ranch Doritos ends up making you crave more Cool Ranch Doritos? Researchers have observed this behavior in rats, noting that junk food not only makes them fat, but reduces their appetite for good food.

“If the same thing happens in humans, eating junk food may change our responses to signals associated with food rewards,” lead researcher Professor Margaret Morris, head of pharmacology from the School of Medical Sciences, said in a press release. “It’s like you’ve just had ice cream for lunch, yet you still go and eat more when you hear the ice cream van come by.”

PICTURES: Junk Food Vs. Junk Food: Reading the Label

Specifically, the rats lost their taste for novelty. Rats raised on healthy diets tend to avoid flavors in which they’ve recently indulged in, a trait known to protect against overeating and promote a balanced diet.

When rats were exposed to diets of pie, dumplings, cookies and cake — with 150 percent more calories, however — they continued going back for more of the familiar flavors, even after they returned to a healthy diet.

VIDEO: Why Junk Food is Addictive

The junk food diet may create changes to the reward circuits in rats’ brains, the researchers said. That circuitry is similar in all mammals, so the implications are likely to be similar in humans.

The study adds to growing research showing how access to junk food may contribute to the worldwide obesity epidemic.