Brain circuit is responsible for people's urge to overeat junk food

The advice to “eat everything in moderation” has long been popular wisdom but for many of us it’s easier said than done.

From gorging on tubs of ice cream to polishing off share-sized bag of crisps, why is it that we tend to eat high-calorie foods with such abandon?

According to new research, there is a reason many of us can’t resist eating more than we should in one sitting, and it’s got nothing to do with being greedy.

A team of scientists at the University of North Carolina (UNC) School of Medicine have discovered a brain circuit found in mammal brains that appears to be linked to our urge to overeat high-calorie foods.

The researchers suggest that the brain circuit overrides signals that tell us to stop eating and instead drives us to continue long after we are full.

They add that the circuit is likely the result of an evolutionary hold that told us to consume as much as possible when food was available so we would have enough fat stored to survive famines.

“Scientists have studied the amygdala – the part of the brain that processes emotions – for a long time, and they've linked it to pain and anxiety and fear, but our findings here highlight that it does other things too, like regulate pathological eating,” said Dr Kash, a UNC neuroscientist involved in the research.

“This circuit seems to be the brain's way of telling you that if something tastes really good, then it's worth whatever price you're paying to get to it, so don't stop.”

The researchers came across the brain circuit during a study on mice that had been engineered to produce fluorescent molecules which would light up when brain activity occurred in relation to eating.

When the scientists fed mice rich, calorie-dense food instead of their ordinary diet, a particular brain circuit lit up.

The researchers suggest that this indicates our impulse to gorge past the point of feeling full is something we’re wired to do.

However, the combination of this wiring and the fact that there is so much high-calorie food available to us now has resulted in an obesity epidemic.

According to the NHS, obesity affects around one in every four adults and around one in every five children aged 10 to 11.

It also estimates that obesity and being overweight contribute to at least one in every 13 deaths in Europe.

As a result, the researchers also wanted to find out if there could be a way to curb overeating.

The team discovered that, when mice were presented with high-calorie foods, the brain circuit encouraged food consumption using a protein called nociception – a signalling molecule in the nervous system.

They found that by using compounds which block nociceptin activity – called nociceptin receptor antagonists – they could curb the desire to binge on calorie-rich foods.

When scientists deleted around half of the mice’s nociceptin-making neurons in the overeating circuit, the animals' bingeing was reduced and their weight remained balanced when they had access to rich food, without affecting their intake of ordinary food.

As a result, the researchers believe their discovery could provide a base for a weight-loss drug that might restrain people’s desire to keep eating junk foods, without interfering with normal eating habits.

Lead study author Andrew Hardaway, an assistant professor of pharmacology at UNC, said, “Our study is one of the first to describe how the brain's emotional centre contributes to eating for pleasure.

“It adds support to the idea that everything mammals eat is being dynamically categorised along a spectrum of good/tasty to bad/disgusting, and this may be physically represented in subsets of neurons in the amygdala.

“The next major step and challenge is to tap into these subsets to derive new therapeutics for obesity and binge eating."