Does the thought of salty fries get your mouth watering? Do you like to nibble salt crystals off pretzels? Research this week shows why you might crave a salt rush – and why some people are wired to eat more salt than they probably should.
Craig Smith from the Florey Institute in Melbourne, Australia and colleagues unveiled the brain’s salt reward system and found it lit up the emotional centre of the brain. The work was published in Proceedings of the National Academy of Sciences.
And at the American Heart Association’s Scientific Sessions meeting in New Orleans, US, Jennifer Smith from the University of Kentucky presented a correlation between variations of the gene responsible for tasting bitterness and salt intake.
Both studies could help people at risk of heart disease and high blood pressure control their salt intake – a big factor in cardiovascular disease, the leading killer of people across the globe.
Researchers have known salt cravings were regulated by the opioid system in the brain for years.
The opioid system is where we process rewards, pain and addiction. Our brain rewards us with natural opioids, such as endorphins, when we’re hungry and eat something for instance.
External opiates also give the system – and us – a rush, such as heroin. These can be extremely addictive and drive cravings.
But no one knew the exact circuits behind salt specifically.
So Craig Smith and his crew starved mice of salt, then administered different opioid blockers before giving the rodents access to salt water.
Two of the blockers didn’t have any effect on the drinking behaviour. Mice given those drank lots of salty water.
But mice given the third blocker, naloxonazine, barely touched it.
This suggests the receptors that naloxonazine binds to are responsible for the salt reward circuit.
The researchers also found the part of the brain of salt-starved mice that lit up when given salty water was the central amygdala, where emotions are processed. When they opioids were blocked in the central amygdala, the mice lost interest in the 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,” Craig Smith says.
“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.”
Wired to eat salt
Jennifer Smith and her colleagues wanted to narrow in on why some people might be genetically predisposed to eat more salt – and suffer heart disease as a result.
They looked at the gene TAS2R38. Variants of the gene can enhance bitterness, and those more sensitive to the taste could be less likely to eat heart-healthy but bitter foods such as broccoli and leafy greens.
Could the same gene affect salt intake too?
The team analysed diet habits of 407 people in rural Kentucky with two or more heart disease risk factors.
Those with gene variants that boosted bitterness perception were nearly twice as likely to eat more than the recommended daily minimum amount of salt but no more likely to eat more sugar, saturate fat or alcohol.
“There is some research suggesting that individuals who taste bitter more intensely may also taste salt more intensely and enjoy it more, leading to increased sodium intake,” Jennifer Smith says.
“Another theory is that they use salt to mask the bitter taste of foods and thus consume more sodium.”
Most of their study participants were white, so the researchers plan to extend their work to wider ethnic groups.
But Jennifer Smith says genetic information may help people choose heart-healthy foods rather than fight their inborn preferences.
“By identifying which gene variant a person has, we may be able to help them make better food choices through education that is personally tailored to them.”
Related reading: Health Check: how much salt is OK to eat?
Belinda Smith is a science and technology journalist in Melbourne, Australia.
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