Anyone who has ever tried to get children to try eating something healthy instead of turning to junk food knows that the siren call of unhealthy food is overpowering. A new study shows that the reaction is chemical and shines light on the growing obesity epidemic worldwide. Consuming a lot of junk food really causes resistance to try new or healthy foods and it weakens self-control, thereby reducing one’s willpower to resist more junk food.
Research recently showed that a junk food diet not only made rats fat, but it also reduced their willingness to try novel foods. The rats would normally have a preference to eat novel things and are actually encouraged to consume a balanced diet.
The study, published in Frontiers in Psychology, shows how eating too much junk food changes rat (and probably human) behavior. The resulting weakened self-control can and often does lead to overeating and weight gain. In other words, developing a taste for junk food makes rats and people not want to eat anything else.
The research team from the University of New South Wales (UNSW) Australia conducted several rat experiments to study dietary preferences. Besides developing an overwhelming preference for junk food, the rats that ate a lot of junk food did not stop eating when full, according to the research.
For the study, the rats were divided into two groups. One group was fed a diet of healthy rat food; the other group of rats was fed a diet of not-healthy human foods like dumplings, cookies, pie and cake.
All of the rats were given drinks of cherry and grape sugar water. The rats were taught to associate the different sugar water flavors with different sound cues, which essentially acted like audio commercials for the sweetened drink. The rats all responded to the sounds at first. However, the healthy-fed rats reached a point where they ignored the cues and would not drink any more sugar water. The junk-food fed rats continued to consumer the sugar water if they heard the sounds.
After two weeks, the rat group fed junk food ended up weighing 10 percent more than the rats that ate healthy food. Clearly, the junk food fed rats did not acknowledge when they had overindulged in the flavored sugar water. By contrast, the rats that regularly consumed healthy foods responded to innate signals to stop eating.
The affect on rats’ food preference lasted beyond the experiment. The research reported that it took a while for the junk food eating rats to resume eating a healthy diet.
The UNSW researcher theorized that the junk diet led to changes in the area of the rats’ brains that makes decisions based on rewards. Given that the brain’s reward circuitry is similar for humans, the results showed the implications of junk-food diets (and the audio cues or ads to grab more) tampering with the ability to limit intake of junk foods.
Noting that eating junk food changes responses to brain signals tied to food rewards, UNSW Professor and study co-author Margaret Morris pointed out that it is comparable to someone who already had ice cream wanting more when the bells of the ice cream truck going by whet their taste buds. Advertisements may have a greater effect on people who are already overweight or prone to indulging in snacks, thereby perpetuating their preference for unhealthy foods and causing resistance to healthy foods in favor of junk food.
By Dyanne Weiss