Junk Food Rewires Brains

Maylin Rodriguez-Paez RN

If you find that you’re not inclined towards healthy foods, don’t be so hard on yourself. It may not be just a lack of will power, discipline, or motivation, after all.

In fact, a new study shows that junk food can actually "rewire" the brains of rats to increase their preferences for junk food.

The results were published in the journal Frontiers in Psychology.

Rats Fed Junk Food Avoid Balanced Diets

Researchers from Australia wanted to test the effect of junk food on weight and food preferences. They assigned rats one of two diets (chow or cafeteria), with the difference being the inclusion of meat pies, cakes, and cookies in the cafeteria group. Weight gain was seen for both groups with the cafeteria group gaining 10% more.1

Both groups were trained to associate flavored waters (cherry and grape) to two different sounds. Each time a specific sound was played, it was a cue for the rats to drink a specific flavor. The chow group responded correctly to sound cues. After drinking grape water, for example, they would ignore the sound cue to continue drinking grape water.

Rats have a natural instinct to avoid overindulgence. On the other hand, the rats in the cafeteria group would drink grape water after hearing the corresponding sound cue, even after they had consumed the grape water. The same reaction was observed with the cherry water.

After two weeks it was apparent that the cafeteria group was not interested in a “balanced diet”, which encourages them to seek novel foods. After they resumed their normal diet, they continued to seek out the junk food given to them during the study and they drank the flavored waters indiscriminately.

Junk Food Rewires Rat Brains

The authors proposed, based on results from other published studies, that in rats from the cafeteria group, changes occurred in the reward section of the brain, which controls decision-making. This could explain why they overindulged in fattening foods.

Hard drugs such as cocaine produce similar changes in the brain. With continual use, a greater quantity is needed to produce a desired “high”. The same relationship has been seen with junk food.2

The Bottom Line

The study was conducted on rats, but it may offer insight as to why many humans tend to overindulge in junk foods. In a day and age when junk food is so common, it can be hard, or even in some cases, impossible to resist.

Is it due to a weak will or a dysfunctional brain? Perhaps it’s the latter or a combination of factors. Whatever the case, it’s a subject well worth investigating.


  1. Front Psychol. 2014 Aug 27;5:852. 
  2. Available at: http://www.scripps.edu/news/press/2010/20100329.html. Accessed March 13, 2015.


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