Have a sweet tooth? Find the answer in your genes.
Cake and cola and cookie lovers may well be able to blame their cravings on a common variant of a gene that controls the brain's ability to sense sugars in the body, a new University of Toronto study suggests. About one in five people has the variant.
The gene may also have implications for a person's risk of getting diabetes.
"In humans this gene functions as a glucose sensor in the brain to regulate appetite or food intake," says U of T nutrition expert Ahmed El-Sohemy, the study's principal author.
"It's involved in the brain's ability to detect sugar, and when (you) have had enough," says El-Sohmey, Canada research chair in nutrigenomics at the school.
People with the variant of the gene GLUT 2 consistently ate more sweets and drank more high-calorie drinks that those with the more common form of it, the study published today in the journal Physiological Genomics found.
The GLUT 2 gene, which also helps regulate insulin release from the pancreas, has long been known to be involved in breaking down sugars in the body.
The study, which involved about 850 subjects, began as a look at the gene's pancreatic function and whether it determined how efficiently the body clears sugar from the bloodstream.
Researchers discovered the gene's neurological role helps determine who will become a chocoholic.
"Surprisingly, we were just looking at the basic characteristics of the people with the variant and without the variant," El-Sohemy says. "And everything was the same – height, weight, physical activity – except their sugar consumption."
El-Sohemy's team recruited two cohorts of subjects for the study.
One group was older, sedentary and overweight; the other included only young, fit and lean individuals.
Yet in both groups, El-Sohemy says, the 20 per cent of subjects with the variant also had significantly higher sugar consumption.
"We looked at their habitual diet ... and sure enough, everything was the same except for glucose (consumption)," he says. "Those who had the rare version ... consumed more sugar."
El-Sohemy says the normal gene probably allows the brain to sense when the body has had enough sugar and suppresses appetite.
Brains regulated by the variant would have a diminished ability to recognize when sugar levels were elevated and would not shut down consumption.
"Traditionally, this gene has been viewed as being expressed in the pancreas, but it turns out it's also expressed in regions of the brain that regulate appetite," El-Sohemy says.
The study offers an example of the role genetics may play in eating habits and obesity, says Diane Finegood, head of nutrition, metabolism and diabetes with the Canadian Institutes of Health Research.
"They are identifying a potentially important connection between the brain and behaviour or the stimulus for behaviours," Finegood says.
"It helps to highlight for the public that there are important connections between the genes and our environments and our behaviour."
El-Sohemy says GLUT 2 would not account for all sweet cravings, and that there may be taste genes also involved in food desires. But almost everyone with the variant would be inclined to eat sweets.
It could also play a role in obesity and diabetes risk.
Among the younger group studied, those with the variant had a significantly higher body mass index, El-Sohemy says. "In the older population, they were all overweight. Still, those who had the variant were slightly heavier."