August 29, 2014
Junk Food Persuades Us To Reject A Balanced Diet, Test On Rats Suggests
John Hopton for redOrbit.com - Your Universe Online
Testing on rats has shown that too much junk food may teach our brains to disregard the need for a balanced diet. Reduced self-control from eating bad food could chart a course to overeating and obesity that becomes increasingly difficult to deviate from.
Research has shown that when rats are given access to a junk food diet, the result is not only weight gain but also a reduced appetite for varied foods. The natural inclination towards a diverse and balanced diet that is widespread in animals, including humans, is impeded and continues to be for some time after junk food consumption is stopped. Natural tendency to avoid over-eating is also decreased.
A team led by Professor Margaret Morris, Head of Pharmacology from the School of Medical Sciences, UNSW Australia, observed that rats provided with a two week diet which included daily access to cafeteria foods such as pie, dumplings, cookies and cake had increased weight of ten percent and displayed significant behavioral changes. They became indifferent when it came to choosing food, and had lost their natural propensity for novelty.
The tests had young male rats associate different sound cues with different flavors of sugar water; one cue for cherry and one for grape. Healthy rats that were used to a good diet would ignore cues related to a flavor they had recently overindulged in. But after two weeks on the junk food diet this built in dietary control was less apparent and the rats stopped avoiding the sound that advertised the over-familiar taste, a habit that continued even after a healthy diet was resumed.
It is thought that a diet of junk food causes changes in the reward circuit parts of the rats' brains, such as the orbitofrontal cortex, an area responsible for decision-making. The brain’s reward responses are similar in all mammals, and so the assumption is that a regular diet of junk food in humans will impair our self-control and make it increasingly difficult for us to say no to harmful foods.
"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," says Professor Morris. "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."
These findings bring additional concern to the well-publicized problems of obesity, which results in the deaths of at least 2.8 million people worldwide every year and contributes to a series of chronic diseases.
In addition, Dr. Amy Reichelt, UNSW postdoctoral associate and lead author of the paper, published in the open-access journal Frontiers in Psychology, suggests that, "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.”
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