Junk Food Not Only Makes You Fat, It Makes You Indifferent About What You're Eating Too: Study

Ring a bell? Just food eventually stops the brain warning you not to over-indulge. Photo: Scott Barbour/Getty Images

Eating junk food not only makes you fat, it also reduces interest in other foods, a key driver in seeking a balanced diet, a study by researchers at the University of NSW has found.

The study, published today in Frontiers in Psychology, helps explain how excessive consumption of junk food can change behaviour, weaken self-control and lead to overeating.

The researchers taught young male rats to link two different sounds with two flavours of sugar water – cherry and grape.

Healthy rats, with a healthy diet, stopped responding to cues for the flavour they’d recently overindulged in. That inborn mechanism normally protects against overeating and leads the body to seek a healthy, balanced diet.

But after two weeks on a diet featuring pies, dumplings, cookies and cake – with 150 percent more calories – the rats’ weight increased by 10% and their behaviour changed dramatically. They became indifferent to what they ate and no longer avoided the sound advertising the over familiar taste, which suggests they lost their natural preference for different foods.

UNSW Professor Margaret Morris, who led the team, said the change lasted for some time after the rats returned to a healthy diet.

“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,” she said.

Professor Morris said all mammals had similar reward circuitry in the brain.

“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 comes by,” she said.

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