Saturday October 18, 2008 (foodconsumer.org) -- A new study published in the Oct 17, 2008 issue of the journal Science suggests that a gene variant has something to do with the obesity epidemic.   But a health observer quickly warned that the genetic effect on the risk of obesity if there is any should be small and people can adjust their lifestyle including their diet to get their weight under control.

The study led by Eric Stice, PhD, of the Oregon Research Institute and colleagues from Yale University and the University of Texas at Austin found some evidence to support the theory that "individuals may overeat to compensate for a hypofunctioning dorsal striatum, particularly those with genetic polymorphisms thought to attenuate dopamine signaling in this region."

The researchers found females with decreased striatal activation in response to the milkshake in the study were at increased risk of weight gain after one year.    But the risk was even greater in those who had both decreased striatal activation and the A1 allele.

The study involved two sub-studies. One enrolled 43 female college students ages 18 to 22 with a mean body mass index of 28.6 while the other involved ages 14 to 18 with a mean BMI of 24.3.

For the study, Stice and colleagues let subjects eat fat and sugar loaded milkshake and measured the striatal activation in response to food intake in the brain using a technique called functional Magnetic Resonance Imaging (fMRI).   Subjects were also tested for Taq1A1 allele.

Early studies found people with this gene variant tend to have a low number of dopamine D2 receptors, meaning they are less likely to get satisfied with the amount of food they eat which would otherwise satisfy those who do not have the gene variant.

Stice and colleagues found females who carry a genetic variation and a weakened "reward circuitry" in their brains or decreased striatal activation in response to food intake were significantly more likely to gain weight after one year.

The researchers said the finding demonstrated that people who have the gene variant and a blunted response to the pleasure from eating food would have to eat energy-dense food (fat and sugar with much fiber) to get satisfied, leading to an increase in the risk of becoming obese.

In an interview with the journal Science, Dr. Stice said his group just completed a new study to see dietary intervention would counteract the effect of the gene variant. The data did not come out, but he said "you could use either behavioral or pharmacological interventions to try to correct this blunted striatal response to food received."

Another study published in the Sep 30, 2008 issue of Nutrition also suggests that just because you have the Taq1A gene variant you do not necessarily have to become obese.

The study led by Barnard ND and colleagues from George Washington University School of Medicine showed at least white people who were positive for Taq1A actually reduced fat intake after 74 weeks on a vegan diet.   But for blacks, the vegan diet did not make much of a difference.

The study did not say whether this vegan diet helped subjects’ weight loss among those who reduced fat intake.   But at least, the results suggested that the white Taq1A carriers do not have to turn to a high fat diet for the eating pleasure.

Although the Stice's study suggests that the gene variant carriers are more likely to over-eat energy dense foods, which could be a cause for obesity, the caloric intake alone does not determine the weight status.  

Colin T. Campbell, Ph.D., a distinguished nutrition professor at Cornell University said Chinese people in rural areas eat 400 more calories than their American counterparts, but few of them are obese.   He noticed two things are different; the Chinese in such areas eat mostly a whole foods, plant-based diet.   In their diet, fat and meat are low while the bulk is grain products and vegetables. They are also more physically active.

Dr. Campbell said a whole foods, plant-based diet plus moderate amounts of physical activity are the only solution to maintaining healthy weight although people who have some genetic variant need to work hard to keep their weight under control.    He said this whole foods plant-based diet is more satisfying and the eaters can eat whatever amounts they want to, but are unlikely to gain weight as showed in many early studies.