Liver gene variants give 'sweet tooth'

A genetic variant in a liver protein increases a person's preference for sweet food.

Scientists at the University of Copenhagen have shown that people with one of two gene variants were nearly 20 percent more likely to seek out sweet snacks.

'This study gives us insight into the molecular basis of the sweet tooth - that's probably the heart of it for me: Why do you have a sweet tooth at a biological level?' Professor Matthew Gillum, a senior author of the study and a member of the Novo Nordisk Foundation Center for Basic Metabolic Research, told Scientific American.

Liver-secreted fibroblast growth factor 21 (FGF21) is a small signalling molecule involved in the digestive system's response to sugar. The study, published in Cell Metabolism, investigated the association between two FGF21 gene variants which earlier research had associated with increased carbohydrate intake, and self-reported preferences for different types of food, including cake or candy. The researchers also investigated lifestyle habits such as smoking, coffee drinking, and alcohol consumption. The 6500 healthy participants were part of a large, Danish study on heart health, and were not on a diet or trying to lose weight.

Participants with either of the two variants were much more likely to consume larger amounts of sweet foods. A separate study by the team in 86 healthy people also showed that levels of FGF21 went up in all participants after the consumption of sugars, but levels were naturally higher at baseline in participants who disliked sweet food.

'We are still working on why the liver would have evolved mechanisms to do this, but hypothesize it may be to limit excess sugar consumption - either to promote diet diversification or to prevent the effects of excess sugar intake,' said Professor Gillum.

These findings are supported by previous studies in rodents and non-human primates, which showed that animals with higher FGF21 levels have a lower preference for sweet food. Yet this is the first study to demonstrate this inverse relationship between FGF21 and a 'sweet tooth' in humans.

'We went into this study with an open question about whether this would be a rodent-specific feature of FGF21 or something we can actually see in people,' explained Professor Gillum.

The research showed no links between FGF21 gene variants and obesity or glucose intolerance. However, it revealed an association between one variant of FGF21 and increased smoking and alcohol consumption. '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 Professor Niels Grarup, a senior author of the study.

Professor Gillum told Scientific American that the researchers plan to study the roles of FGF21 in humans further: 'We want to look at people who are completely deficient in FGF21 and answer: Will they be alcohol or sugar superfreaks?'