Junk food makes you want to eat more junk food, study says

Rats who ate a diet high in junk food not only gained weight, according to a new study, but they also lost their appetite for nutritious foods - an internal mechanism that normally keeps animals from overeating and maintaining a healthy diet.

The study, which was published in Frontiers in Psychology, might explain why overindulging in not-so-nutritious foods can lead to changed eating habits and a lack of self control.

"The interesting thing about this finding is that if the same thing happens in humans, eating junk food may change our responses to signals associated with food rewards," said Professor Margaret Morris, Head of Pharmacology from the School of Medical Sciences, UNSW Australia. "It's like you've just had ice cream for lunch, yet you still go and eat more when you hear the ice cream van come by."

Healthy rats know when to stop eating

For the study, Morris taught young male rats to associate certain sound cues with various flavors of sugar water. Rats that were raised on a healthy diet inherently knew when to stop - they didn't respond to the cues that were associated with a flavor they had recently indulged in.

But rats that had been on a two-week diet of junk food not only gained weight, but they stopped ignoring the sound cues when they were technically "full" on one flavor.

"The researchers think that a junk diet causes lasting changes in the reward circuit parts of the rats' brain, for example, the orbitofrontal cortex, an area of the brain responsible for decision-making," stated a press release on the study. "They say these results may have implications for people's ability to limit their intake of certain kinds of foods, because the brain's reward circuitry is similar in all mammals."

Source: Frontiers