Why do some of us have a sweet tooth? Study investigates

It is well-known that too much sugar in our diet is not good for us. However, why do some people get a craving for sweet foods while others find it easier to abstain? A new study investigates.

The Centers for Disease Control and Prevention (CDC) warn that many people in the United States consume far too much sugar, and that this can cause major health conditions including heart disease, type 2 diabetes, and obesity.

However, while some of us find it relatively easy to abstain from eating cake, for others, this can be more complicated. People who have a so-called sweet tooth may find it harder to avoid sugar - but is this a matter of willpower, or could there be a biological explanation for sugar cravings?

A previous study in rodents has shown that a hormone secreted by the liver, called FGF21, "suppress[es] the intake of sweets." Similarly, another study on primates has suggested that the same hormone can reduce the appetite for sweets.

In this context, new research - recently published in the journal Cell Metabolism - investigates whether FGF21 has the same effect in humans, and if fluctuations in the hormone can explain sugar cravings.

People with FGF21 variants 20 percent more likely to have a sweet tooth

The researchers were led by Matthew Gillum, assistant professor of biological sciences, and Niels Grarup, an associate professor of metabolic genetics, both from the University of Copenhagen in Denmark.

The research examined the data from an existing study of more than 6,500 Danish participants, called the Inter99 study. Using the participants' self-reported information, the Inter99 research looked at their metabolism, lifestyle, and dietary intake.

In the Inter99 study, the researchers also measured levels of cholesterol and glucose in the blood of the participants. In addition to these data, for the new research, Grarup and Gillum sequenced the FGF21 gene in an attempt to decode it and its variants.

The researchers genotyped and examined more closely two variants of the gene that had been previously linked to a higher consumption of carbohydrates - FGF21 rs838133 and rs838145. The study found that people with either of the two variants were 20 percent more likely to regularly eat a large amount of sweets.

"These variants are very solidly associated with sweet intake," says Gillum. Additionally, the study found that these variants correlated with a higher level of alcohol intake and smoking, although more studies are needed to confirm this link.

FGF21 fasting levels 50 percent higher among those who dislike sweets

The authors also conducted a clinical study to confirm their first round of findings.

They examined the link between fasting levels of FGF21 and a preference for sweet food among 86 "young, healthy, and lean" participants.

Participants filled in a questionnaire that asked them about their liking of sweet, salty, and fatty-sweet food. The researchers measured the blood levels of FGF21 after the participants had fasted for 12 hours.

They then asked the participants to consume the sugar equivalent of two cans of Coke, and they continued to monitor their hormone levels over a period of 5 hours after the sugar intake.

Immediately after the fasting period, FGF21 levels were 50 percent higher among those who did not like sweets than among those who did. After consuming sugar, however, FGF21 rose to approximately the same level in both groups.

In the near future, Gillum and Grarup hope to carry out similar research but on a much larger scale. This would allow them to better grasp the effects of an increase and decrease in FGF21 blood levels.

A larger study would also enable the researchers to examine the link between the hormone and various metabolic diseases, such as obesity and type 2 diabetes.

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

Gillum also weighs in on the findings, saying that the study offers "a really surprising insight into the potential hormonal basis of the sweet tooth."

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