Sugar lover? A hormone is responsible for whether you have a sweet tooth or not

Suffer from chocolate cravings? Like to indulge on sweets? Scientists have found that a hormone secreted by the liver after eating sugary foods may determine who has a sweet tooth and who doesn't.

People with particular variants of a hormone called FGF21 are around 20% more likely to be the highest consumers of sweets such as ice cream and chocolate, according to researchers at the University of Copenhagen.

"The data, mined from a study of the lifestyles and metabolic health of 6,500 Danish individuals, is a really surprising insight into the potential hormonal basis of the sweet tooth," says Professor Matthew Gillum, who led the study.

The research, published in Cell Metabolism, raises new ideas about the role of the liver in controlling what we eat.

Once food has passed through the stomach and intestine, the next organ nutrients encounter is the liver. In addition to signaling that it's time to put the sweets down, the researchers speculate that the liver could also secrete other hormones that guide food choices more broadly.

"How do we decide what and how much to eat? Maybe satiety consists of different pathways that control different types of nutrients," said Gillum. "This study has opened my mind to how this regulatory system might work."

Gillum and collaborators at the University of Iowa first discovered the role of liver-secreted FGF21 in regulating sweet intake in 2015 in studies of rodents.

To find out whether the hormone would play the same role in people, Gillum and the other researchers used previous study as a data source. The study had collected self-reported dietary intake as well as measures of bloodstream cholesterol and glucose from participants. The scientists then sequenced the FGF21 gene in study participants.

They zoomed in on two variants of the gene that in earlier research had been associated with increased intake of carbohydrates.

They found that individuals with either of these two variants were much more likely to consume larger amounts of sweets.

The study did not find an association with obesity or type 2 diabetes, however.

"Dozens of factors have been found to be involved in metabolic disease. In this study, we are just looking at one little piece in a big puzzle," said co-lead researcher Niels Grarup.

To get a better sense of how the FGF21 hormone behaves in the body to regulate sweets, the researchers set up a clinical study to analyse how it ebbs and flows in the blood of volunteers in response to sugar intake.

Prior to testing, they asked participants to rate themselves as having a sweet tooth or not. They focused the study on 51 subjects who were the most extreme likers and dislikers of sweets.

They measured FGF21 levels after a 12-hour fast, and then monitored changes in the hormone levels over five hours after participants drank sugary water, which contained around as much sugar as two cans of Coke.

Those who disliked sweets had fasting FGF21 blood levels 50% higher than their sweet-toothed counterparts. However, after the sweet drink, FGF21 blood levels followed the same trajectories and rose to about the same levels in both groups.