It seems simple enough: if you eat only as many calories as you burn, you won’t pack on the pounds. Yet for many, balancing this equation is anything but easy. Obesity has become one of the most significant public health threats facing the United States and other developed countries. One-third of adults in the United States today can be considered clinically obese.
While lifestyle choices are certainly important, research has shown that genetics plays a significant role in determining a person’s propensity for being overweight or obese. One especially potent variant in the FTO gene has been consistently linked with weight in Europeans.
In a study of Scottish children published online yesterday by the New England Journal of Medicine, researchers suggest that this FTO variant may contribute to obesity by leading kids to chose foods that, pound for pound, pack a more powerful calorie punch.
Seventy-six kids between the ages of four and 10, selected from a larger study of 2,726 children who were having their height, weight, and FTO genotypes evaluated, also had their energy expenditure and food intake measured.
There was no difference in the number of calories burned while at rest between children who carried the higher weight-associated version of FTO and those who did not. Energy burned due to physical activity was actually higher for carriers than non-carriers. This suggests that the FTO variant isn’t affecting the basal metabolism rate or conferring a proclivity for a sedentary lifestyle.
There was also no difference in the total weight of the food ingested by the kids with the version of FTO linked to obesity. But these children did consume more calories than their non-carrier friends. The foods they chose during the test meals had “higher energy density” — they contained more calories per unit weight.
The authors note that most obesity disorders caused by defects in single genes (such as MCR4) affect eating behavior. These new results, and those of other studies (a few examples here, here, here and here), show that the common FTO variant is no different. It is unclear, however, whether FTO affects appetite regulation or the ability to sense how much food has been ingested.
In an accompanying editorial in NEJM, Dr. Rudolph Leibel says that although the proportion of obesity in the general population that can be attributed to variation in the FTO gene region is high, it’s probably still not enough to start using this SNP as a clinical screening tool.
But he goes on to say that in the not-so distant future more variants such as this one will be found and physicians will be able to assess a “score” based on maybe 15 to 20 genes to predict an individual’s risk for obesity.
“The important role that environment plays in enabling or resisting such susceptibility is clear evidence that such risk can be modified,” Leibel concludes.