Junk food shown to change eating behaviours

Junk food changes eating behaviour in rats, causing them to stop seeking out novel foods, a study conducted by the University of New South Wales (UNSW) has shown. The researchers say this could explain why excessive junk food consumption can weaken self-control and lead to overeating and obesity.

In the first part of the study, young male rats were taught to associate two different sound cues with two flavoured sugar waters - cherry and grape. If the rats had recently indulged in a particular flavour, they stopped responding to cues linked to that flavour.

This mechanism is reportedly widespread in animals and stops them overeating and ensures they eat a balanced diet.

In the second part of the study, the rats were given daily access to cafeteria foods such as pies, dumplings, cookies and cakes for two weeks. They gained weight and, according to the researchers, their behaviour changed dramatically. They no longer avoided the sound associated with a particular flavour, indicating that they had lost their natural preference for novel foods.

The researchers say this changed behaviour even continued on for some time after the rats’ diet was changed back to a healthy one.

“We think that a junk diet causes lasting changes in the reward circuit parts of the rats’ brains, for example, the orbitofrontal cortex, an area responsible for decision-making,” said UNSW Professor Margaret Morris, Head of Pharmacology in the School of Medical Sciences.

“Because the brain’s reward circuitry is similar in all mammals, this could have implications for people’s ability to limit their intake of certain kinds of foods.

“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.”

Dr Amy Reichelt, first author of a paper on the study, says advertisements for junk food may have a greater effect on people who are overweight, making it harder to resist junk food purchases.

The paper is published in Frontiers in Psychology. The work was supported by an NHMRC Project Grant.