Junk food doesn’t just make you fat (though it does a great job of that). It might also make you boring to eat around.
That’s what a new study published in Frontiers in Psychology suggests. The research team was interested in how a “cafeteria diet”—one loaded with cheap, high-calorie food—affects the animals’ natural preference for novelty.
"Exposure to this Western diet appears to change the way the brain responds to these cues,” says study author Margaret Morris, professor at the University of New South Wales. “Their ability to discriminate what they’d just eaten is impaired, and we think that might contribute to overconsumption…if you don’t remember what you just had, maybe you keep eating.”
Two groups of rats were fed different diets for two weeks. One group was given low-fat rat chow, while the other group had its choice of the chow plus a buffet of fatty junk foods, like cookies, dumplings, and cake.
After two weeks, the junk food rats got fatter and more blasé.
Humans and animals have a natural preference for novelty, says Morris. This notion of "sensory-specific satiety" is one we’re all familiar with: if you crush a bowl of pasta and are then offered a choice of steak or more pasta, you’ll choose the steak because you’re sated on the pasta front and crave something different.
But after the rats chowed down for two weeks, researchers tested this response. They let the rats binge on either a cherry or grape Kool-Aid drink and then offered them a choice between the two flavors a couple hours later. Rats on the healthy chow consumed more of the flavor they hadn't just binge-drank. But the junk food rats drank the same amount of both beverages. Even after researchers put the junk food rats on an all-chow diet for a week, the rats continued to show no preference for one drink over the other, “which suggests that there’s something going on in the brain of the animal that persists beyond the exposure to that unhealthy diet,” she says.
Results of rat studies don't necessarily translate to humans, and research is mixed about whether sensory-specific satiety or memory is impaired in obese people. But at the risk of losing your taste for variety, you might consider skipping the junk food aisle.