Researchers are discovering behavior in rats that when they're given a steady diet of junk food, it not only makes them heavy, but reduces their appetite for healthier food, Discovery News reported on Wednesday.
"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, according to Discovery News. "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."
Specifically, the rats lost their taste for novelty food. Rats raised on a healthy diet tended to avoid flavors they recently ate, a trait known to protect against overeating and lead to a balanced diet. When rats were given a diet of pie, dumplings, cookies and cake - with 150 percent more calories - they continued going back for more of the unhealthy flavors, even after they returned to a healthy diet.
The rats were also given cherry and grape flavored sugar water to drink, and found up weighing 10 percent more than their healthy-eating counterparts, according to Newsweek.
The research team taught the rats to associate cherry and grape sugar water with different sound cues. The healthier rats responded appropriately to the cues, for example, they just consumed sugar water and when they heard a second cue for it, they wouldn't drink any more. But the junk food-fed rats would drink the sugar water at any cue, even if they had just consumed a lot of it.
In conclusion, the researchers found that junk food-fed rats don't realize when they've overindulged in food or drink, whereas they healthy rats stop responding to food they just consumed.
The junk food diet may create changes in reward circuits in rats' brains, the researchers found. The circuitry is similar in all mammals, so the results are likely to be similar in humans, according to Discovery News.
