Junk Food Diet Keeps Rats from Seeking Out New Foods

It’s no secret that high-fat and calorie-rich foods are a major contributor to weight gain and obesity. But a junk food diet doesn’t just pack on the pounds — it may actually reduce a person's desire to eat a more diverse diet.

Brains are wired to not overeat too much of one thing and instead to seek out different foods. However, a new study has found that rats on a junk food diet appear to lose the desire for other kinds of food.

In a recent study published in Frontiers in Psychology, researchers from Australia showed that rats eating a diet of high-calorie foods like cookies, pie, dumplings, and cake for two weeks not only gained weight but also lost their desire to seek out different foods. A diet of diverse foods is typically a healthier diet because it means that you’re not eating too much of any one item.

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Researchers conditioned young male rats to associate different sound cues with either cherry- or grape-flavored sugar water. Healthy rats eventually stopped responding to cues for flavors that they had recently overindulged in. This natural mechanism limits overeating.

But when researchers put rats on an unhealthy diet of high-fat foods for two weeks with 150 percent more calories than the healthy diet, the rats became indifferent to diverse foods and would continue to eat the flavored water they had recently indulged in. Even after being put on a healthy diet, these junk food rats didn’t appear to seek out new flavors.

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“Rats are trained so that different sounds cues mean certain types of food are available. As expected, rats on a healthy diet decrease responding to a cue linked to a food that they had recently eaten,” said study author Margaret Morris, head of pharmacology at the University of New South Wales.

“The rats exposed to [a high-fat] diet responded equally to both cues,” Morris said, “regardless of whether they had previously eaten one of the foods until they were full.” That behavior change was surprising, she said.

“The work suggests that consumption of junk foods may make you relatively indifferent to novel food, which may encourage overconsumption. Also that you may overeat when exposed to signals linked to palatable foods.” — Margaret Morris, University of New South Wales

More than one-third, or nearly 80 million, of U.S. adults are obese, according to the Centers for Disease Control and Prevention. Obesity is compounded by related negative health conditions like diabetes and a higher risk of heart disease.

Obesity also dramatically raises healthcare costs — people who are obese spend almost $1,500 more on healthcare every year than people of normal weight. These findings suggest that junk food may trap people who overeat in a diet spiral of unhealthy foods.

“The work suggests that consumption of junk foods may make you relatively indifferent to novel food, which may encourage overconsumption,” Morris said. “Also that you may overeat when exposed to signals linked to palatable foods, so an obese person may be more sensitive to advertising for foods like ice creams and chocolate bars.”

In the future, researchers would like to study the effects of interventions like a longer diet timeline or exercise.

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This study didn’t look at why a junk food diet has this specific effect on eating habits, but other studies have shown that certain parts of the brain activated by drugs are also activated by images of junk food.

Researchers have already linked pathways in the brain connected with drug abuse to overeating. It seems that the Pringles slogan “once you pop, you can’t stop” may hit a little too close to home.