Craving chips with gravy? Researchers say they know why.

A study from Deakin University has shown a specific circuit in the brain’s opioid system that appears to be responsible for making us seek out salt.

High blood pressure (which is linked to salt intake) accounts for about half of all strokes, heart disease and chronic kidney disease deaths. 

“Modern western diets high in salt also tend to be high in things like fat and sugar – which have also been shown to possess addictive properties. Put these three ingredients together and you have an almost irresistible recipe for obesity,” says lead researcher Dr Craig Smith.

“Our bodies have multiple forms of ‘natural opioids’ – those molecules released after you enjoy a particularly energetic session of exercise (or love-making), drinking water when thirsty or eating salt after sweating.

“Interestingly, these same molecules also control our craving of these rewards. Although scientists know that the opioid system regulates salt seeking, the exact circuit has, until now, remained a mystery.”

Using mice that had salt removed from their diet, Dr Smith and the team used three separate opioid blockers to work out which specific circuit was activated when the mice drank salty water.

“Two blockers did nothing. But a third, naloxonazine, drastically reduced the amount of salt consumed by the animals,” he says.

Although opioid receptors are found throughout the brain, giving salt-depleted mice access to salty water activated receptors in a specific brain area - the central amygdale, the emotional centre.

This allowed the researchers to block opioids only in that particular brain region, and the salt-depleted mice were no longer interested in drinking salty water.

“These findings open the way for us to study this salt seeking circuit in humans using magnetic resonance imaging and other techniques, to then develop targeted drugs to inhibit salt craving and promote more healthy dietary choices,” Dr Smith said.

“If processed food producers are slow to respond to the need to reduce salt in their products, this could be another way to lower deaths associated with high salt intake.”

Opiates activate the same receptors in the brain that are stimulated by salt – only much more strongly than even the most delicious burger and fries. Just as future treatments might reduce salt craving, they might also reduce an addict’s craving for heroin. 

The research ­has been published in the early edition of Proceedings of the National Academy of Science.