Bad diets affect brain by decreasing self-control, study shows

UNHEALTHY diets “reprogram” the brain to favour further bad food choices, and the effects happen long before unhealthy eating causes weight gain — but luckily, there is a way to reverse the negative effects.

A diet of junk food decreases self-control with food choices, new research shows.

JUNK food diets “reprogram” the brain to favour further bad food choices, and the effects happen long before unhealthy eating causes weight gain.

New research being presented on Monday at the Australasian Neuroscience Society Annual Scientific Meeting in Sydney is showing that a high-fat, high-sugar diet decreases self-control with food choices, affects memory and increases vulnerability to anxiety.

But importantly, exercise and returning to a healthy diet can largely reverse many of the effects.

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“People think about obesity as being a moral problem; that people are fat because they have poor self-control,” said Dr Ian Johnston, of the University of Sydney’s School of Psychology.

“What my data has shown is that obesity seems to come after people are exposed to bad food.

“It’s reprogramming the brain into the choices you make about how you eat.”

Dr Johnston’s laboratory used delayed gratification tasks with sweetened condensed milk for six weeks in rats, showing those that couldn’t resist sweet treats were more impulsive with their food choices. But a further six weeks later, after they returned to a healthy diet, they had original levels of self-control.

Next, they ranked a group of rats for impulsivity and gave them a buffet of supermarket junk food for a month. The researchers found that the amount of junk food rats ate predicted the change in their self-control and how much weight they would gain.

Data shows obesity comes after people are exposed to junk food Picture: Thinkstock

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“Self-control is the flip side of impulsivity,” Dr Johnston said. “This is how dieting works: delaying immediate gratification now for a long-term gain. This feeds into the idea that if we want people to lose weight, then we really need to make it harder for them to access junk food.”

Meanwhile, Monash University researchers have scanned the brains of obese and normal-weight people while they made food choices. They watched what parts of the brain “light up” when considering options, and when they are rewarded with a taste of unhealthy or healthy drinks.

Monash Institute of Cognitive and Clinical Neurosciences Associate Professor Antonio Verdejo-Garcia, who will present his findings today, said in obese people, there was poorer communication between the parts of the brain controlling hunger and other areas controlling reason.

“If we can understand the mechanisms of why people consume more energy, then we can offer cognitive training that empowers people to make better decisions when it comes to food,” he said.

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