Junk food 'addictive', new study shows

A study of rats who had previously gorged on fatty food showed they would rather go hungry than eat a healthier pellet-based alternative. Photo / NZ Herald

SYDNEY - Junk food can be addictive, an Australian study shows, indicating why for many people the habit can be hard to break.

Rats allowed to gorge on foods rich in sugar and fat put on weight during a two-month study, and also become "anxious" when this food was replaced.

University of South Australia post-graduate student Zhi Yi Ong found her furry test subjects would also opt to go hungry rather than eat a healthier pellet-based alternative.

"It seems like the desire for junk food has overridden their hunger signals, they would rather eat nothing ... than consume the chow as their energy source," Ms Ong said.

"... We've seen junk food can be addictive so it is possibly better to consume not too much junk food."

The rats were allowed to eat their fill of a variety of biscuits, hazelnut spread, peanut butter, sugar-loaded cereals along with cheese and bacon-flavoured snacks.

They were then monitored over three days when this food was replaced with pellets.

Over this time, the junk food-fed rats ran around more than a group of control rats who had only ever eaten the pellets.

"When not with the junk food they became more anxious ... they were probably suffering from junk food withdrawal," Ms Ong said.

While the initial research focused on the rats' behaviour, the next phase will look for signs of increased dopamine processing in their brains.

Previous studies have shown how foods high in sugar and fat can prompt the release of this neurotransmitter in the brain's central reward pathway - the same process exploited by illegal drugs.

"We're speculating junk food can down-regulate (desensitise) the reward pathway in our brains," Ms Ong said.

"So if you have consumed too much, you have to consume more and more in order to feel the same happy feeling."

The research was released at an Adelaide meeting of The Australian Society for Medical Research.

- AAP