Junk food diets could stop people craving healthier food

Scientists warn that a diet full of fatty junk food and sugary treats could actually work to destroy our urge to consume healthy food products.

An Australian study published in the journal Frontiers in Psychology with rats found that not only did the rats gain significant weight eating junk food, it seemed to kill any desire for them to eat healthier food. This could perhaps help to understand behavioural changes in people that regularly eat ‘bad’ foods and appear to exhibit low willpower, putting them at risk of overindulging and obesity.

The researchers believe that by consistently eating junk food, this has a big impact on the reward circuit areas of animals’ brains. One such part affected they say is the orbitofrontal cortex, an area associated with decision-making. The experts involved in the study say the findings may have implications for a human’s ability to limit eating certain foods due to the fact the reward circuitry is similar in every mammal.

Professor Margaret Morris, from the University of New South Wales, said: “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. 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.”

For two weeks the team involved in the study fed one group of rats healthy rat food, with a second group being access to unhealthy human foods such as pie, dumplings, cookies and cake.

All of the rats were given cherry and grape sugar water to drink. The rats eating junk food were consuming 150% more calories and their weight had increased by 10% after the fortnight.

Within one particular experiment, scientists managed to teach the rats certain sound cues to link to either drink. Interestingly, if the rats given healthy food had heard the sound cue for grape sugar water after already just drinking it, they would not drink any more of it. Meanwhile, the junk food-fed rats responded different to the sound cues.

Even if they had just drank a lot of the grape sugar water, the sound cue for said drink would still somehow make them drink more of it. The same pattern was found for cherry sugar water.
Therefore it would seem that junk food-fed rats responded to sound cues and were unable to comprehend they had just overindulged in something (in this case the flavoured sugar water).

Basically, their natural preference for novelty had vanished and no longer avoided sounds linked to an overfamiliar food or taste, happy to continue indulging on what they were already eating.

This was even apparent for a significant period of time after the rats went back to a healthier diet. In comparison, the healthy rats were found to actually stop responding to the food they had just consumed.

“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.”

Dr Amy Reichelt, lead author of the paper, commented: “As the global obesity epidemic intensifies, advertisements may have a greater effect on people who are overweight and make snacks like chocolate bars harder to resist.”