You have at least one memory from your childhood featuring your mom or your grandmother or some other well-meaning adult admonishing you in a harsh tone. “Don’t eat that! It will spoil your appetite!” It might have been cookies, or candy or chips. Inevitably, it was very close to dinner time. And odds are, you weren’t pleased by the words.
As it turns out, junk food really might spoil your appetite — on a more permanent basis.
Researchers at the University of New South Wales Australia conducted several studies to see how junk food would impact rats’ weight and dietary preferences. Of course, they found the obvious—junk food “makes rats fat.” But they also determined that junk food-fed rats experienced a reduced desire for novel foods, which is important as this appetitive tendency, innate in animals, typically encourages rats’ to pursue a balanced diet.
“Eating junk food seems to change the response to signals that are associated with food reward,” commented Prof. Margaret Morris, Head of Pharmacology from the UNSW Australia’s School of Medical Sciences and a study co-author.
How did the researchers come to this conclusion?
For several weeks, the team fed one group of animals a diet of healthy rat food, and they fed another group of rats a diet that included not-so-healthy human foods such as pie, dumplings, cookies and cake. Both groups of rats were also given cherry and grape sugar water to drink. The junk food-fed rats wound up weighing 10 percent more than their healthy food-fed counterparts.
In one of the experiments, the team taught these rats to associate cherry and grape sugar water with different sound cues. The healthy rats responded appropriately to the sound cues—that is, if they had just consumed grape sugar water and then heard another cue for grape sugar water, they wouldn’t drink more of it. Junk food-fed rats, on the other hand, would respond to sound cues in an unhealthy manner—if they heard a noise associated with grape sugar water, they would drink said sugar water even if they had just consumed a lot of it. (The same findings hold for cherry sugar water.)
In other words, it appears junk food-fed rats don’t seem to realize when they’ve overindulged in a food (the flavored sugar water); instead, they respond to the sound cues just the same, whereas healthy rats stop responding to the food they just ate.
“We know a lot about food and nutrition and what we should be doing, and yet we’re getting fatter and fatter,” Morris says. “Our sort of diet appears to override an animal’s ability to know it’s just eaten something—they’re just eating indiscriminately, if you will.”
In another experiment, the researchers wanted to see whether the apparent disruption of the reward mechanism persisted after the junk food-fed rats were placed on a healthy diet. Even after a week on healthy rat chow, the formerly junk food-fed rats still acted the same way, treating both solutions indiscriminately, according to Morris.
“It suggests that whatever changes happen in the brain may persist for a while,” she says.
The study, while pertaining to rats, has a lot of troubling implications for humans. Rat behavior often gives insight into human behavior—which means we should think deeply about junk food’s psychological and public health impacts.
Science is constantly offering us new perspectives on our health and our foods. FoodFacts.com can say with confidence that those new perspectives simply uphold what nutritionists, dietitians, researchers, and educated consumers have known all along. Junk food is nutritionally vacant. What it does provide, unfortunately, are high levels of sugar, salt and fat, contributing to obesity, diabetes and heart disease. And according to the study detailed here, it can interfere with our normal tendencies to balance our diets, thus leading to more of the same. Now that’s a new perspective — not to mention yet another significant reason to stay far away from junk food.