TORONTO - For those who have a sweet tooth and wonder why they're so drawn to sugary foods and beverages, the answer could be that it's all in the genes.
Researchers at the University of Toronto have found that a genetic variation may be driving some people to consistently consume more sugar compared with those who pass on the toothsome treats.
In a study of about 700 subjects, published in the May issue of the journal Physiological Genomics, the researchers found that a variation of the GLUT2 gene is linked to habitual consumption of sugar.
The gene controls sugar entry into cells, and the findings may help explain individual preferences for foods with a high sugar content, said senior investigator Ahmed El-Sohemy of the department of nutritional sciences.
"Essentially what we found is that individuals who have a version of a gene called GLUT2 ... consume more sugar just as part of their habitual diet," El-Sohemy said in an interview Tuesday.
"Obviously, it doesn't explain fully why some people crave sugar and others don't, but it provides a previously unknown mechanism to explain that."
Cravings for foods high in sugar vary from person to person, but the reasons are still unclear, he said, noting that food preferences are influenced by the environment as well as genetics.
"We think the one variant that's associated with higher sugar consumption is associated with impaired (sugar-) sensing ability," he said.
For instance, previous studies that compared normal lab mice to those that had been genetically altered to carry the GLUT2 variant found a huge difference in behaviour between them: when liquid glucose (sugar) was injected into the rodents' brains, the normal mice stopped eating; the genetically altered animals continued to eat.
"That suggests that their brain that lacks this gene is unable to sense glucose, and they're unable to regulate their food intake," he said.
To conduct the study, El-Sohemy's team tested the effects of the genetic variation in two distinct populations: one consisted of older adults who were all either overweight or obese, while the other was made up of generally healthy young adults who were mostly lean.
The researchers assessed the first group's diet by recording all foods and beverages consumed over a three-day period, then repeated this three-day food record two weeks later to ensure its validity. Participants were interviewed in person during the two visits to research centres.
Participants in the younger, leaner group filled out a questionnaire that asked about foods and beverages typically consumed during a one-month period.
To check for the presence of GLUT2 gene (glucose transporter Type 2), the researchers took blood samples from participants and extracted DNA.
The researchers then compared each person's food intake data with their GLUT2 status and found those in both groups with the genetic variation typically consumed more sugar, including sucrose (table sugar), fructose (simple sugar such as corn syrup) and glucose (carbohydrates), regardless of age or sex.
Food records from the first group showed that older individuals with the genetic variation took in more sugars than older counterparts without GLUT2.
Individuals in the younger population who carried the variant also were found to ingest more sugary foods than their non-variant counterparts.
"From what we were able to ascertain, the types of food that they generally consume contribute to the extra sugars," El-Sohemy of younger, leaner subjects. "And it looked like they were more likely to consume sweetened beverages and sweets, things like chocolates, cake, candy."
There were no differences in the amount of protein, fat, starch or alcohol consumed by either group of subjects, no matter their genetic makeup.
El-Sohemy said the genetic variation was found in about 20 per cent of participants in both groups, suggesting that one in five Canadians could carry the sweet-tooth gene.
"These findings may help explain some of the individual variations in people's preference for sugary foods," El-Sohemy said. "It's especially important given the soaring rates of obesity and diabetes throughout much of the world."
