What and how much we eat is not always up to conscious choices. Sometimes, it's really just down to our genetic makeup "dictating" our nutritional needs.
Recently, evidence has emerged that a certain variant of the gene — or the FGF21 A:rs838133 minor allele — may dictate how much we like sugary products.
In a study whose results have now been published in the journal Cell Reports, first author Timothy Frayling — from the University of Exeter Medical School in the United Kingdom — and colleagues suggest that the gene variant that "prompts" us to eat more sweets might concomitantly drive a decrease in body fat.
As the researchers mention in the paper, their study was, in part, prompted by the data offered by three previous genetic studies.
They demonstrated "that the carbohydrate preference [driven by this variant of the FGF21 gene] was specific to sugary products and may also increase alcohol intake."
Just as they confirmed the findings of the previous three studies, Frayling and team encountered a surprise: the same allele responsible for upping our intake of candy also appeared to help bring our levels of body fat down.
"We were surprised that the version of the gene associated with eating more sugar is associated with lower body fat," says Frayling.
Gene variant influences sugar intake
To reach their conclusions, the researchers analyzed the biological data of 451,099 people. They accessed the data through the U.K. Biobank, which is a large international resource of biological samples and data.
"Because this study has so many people in it, it gave us enough individuals to be confident in the associations we were seeing," notes study co-author Niels Grarup, from the University of Copenhagen in Denmark.
Frayling and colleagues investigated the associations between different FGF21 gene variants and people's diets, body compositions, and blood pressures.
"The data," says Grarup, "included a food frequency questionnaire from 175,000 people and blood pressure measures for everyone included in the analysis."
Expression of the FGF21 gene leads to the production of the hormone of the same name, which is made in the liver and has a pronounced metabolic function.
The hormone normally signals the hypothalamus to downregulate intake of sugar and alcohol, "stimulates glucose uptake," and increases sensitivity to insulin.
This study revealed that the A:rs838133 allele of the FGF21 gene raises the consumption of both sugar and alchohol. But at the same time, it is also linked to lower overall body fat.
Less body fat, different distribution
That said, this seemingly positive point does have a downside: a concentration of fat in the upper part of the body, which can cause higher blood pressure.
"This [finding] goes against the current perception that eating sugar is bad for health," explains Frayling.
"[This gene variant] may reduce body fat because the same allele also results in a lower consumption of hormone and fat in the diet."
"But whilst this version of the gene lowers body fat, it also redistributes fat to the upper body, where it's more likely to cause harm, including higher blood pressure."
According to the authors, this version of the FGF21 gene is quite common, with approximately 20 percent of the population in Europe carrying two copies of this allele. Because of this, they argue, it's important to understand how this and other variants of the gene can influence weight and the distribution of body fat.
As for individuals carrying the gene variant investigated in this study, Frayling and team say that they shouldn't be too worried about its impact on their health.
Although they noted that the upper body fat distribution influenced by the presence of this allele can cause higher blood pressure, the researchers note that the rise is not significant — under a third of a millimeter of mercury on the blood pressure charts.
One gap that the researchers would now like to address is understanding exactly how FGF21 influences how much body fat we have, and how it is distributed over the body.
Another issue that they want to address is the current interest shown by pharmaceutical companies in manipulating the FGF21 hormone, which has been singled out as a potentially viable approach in the treatment of diabetes.
"Our studies could refocus those efforts by revealing potential benefits and unintended side effects of manipulating this hormone," Frayling explains.