A way to block a "sweet tooth" may be in prospect after scientists identified a liver hormone that suppresses the desire for sugar.
Research on mice and monkeys showed that the hormone, FGF21, signals the brain to avoid seeking sweet foods.
Harnessing the effect, possibly by copying the the hormone's action with a drug, could help patients who are obese or suffering from Type 2 diabetes, scientists believe.
Although certain hormones were already known to regulate appetite, this is the first one that is specific to sugar consumption.
Dr Matthew Gillum, one of the scientists from the University of Copenhagen in Denmark, said: "We never imagined that a circulating, liver-derived factor would exist whose function is to control sweet appetite.
"We are very excited about investigating this hormonal pathway further."
The study, published in the journal Cell Metabolism, showed that FGF21 exerted a surprisingly powerful effect. In monkeys, a single dose caused them to lose interest in sweetened water almost immediately.
Tests in mice revealed that the liver produced the hormone in response to sugar intake. After entering the bloodstream, FGF21 suppressed sugar appetite by acting on the hypothalamus region of the brain.
The hormone was already known to enhance insulin sensitivity, making it easier for the body to keep blood sugar at a healthy level.
"Now there's this dimension where FGF21 can help people who might not be able to sense when they've had enough sugar, which may contribute to diabetes," said co-author Lucas BonDurant, a Phd student from the University of Iowa in the US.
The research showed that FGF21 did not reduce intake of all sugars - sucrose, fructose and glucose - equally, and did not affect consumption of complex carbohydrates.
One reason FGF21 exists in animals could be to improve diet quality, said the scientists. Another possibility, since sugar can ferment, was that it helped the liver protect itself from excess alcohol.
The FGF21 pathway involves a molecule called carbohydrate responsive element-binding protein (ChREBP), a key regulator of glucose metabolism and fat storage.