Can a gene make you overeat? According to a new research study led by PCRM president Neal Barnard, M.D., a single gene may cause people to overeat, even to the point of obesity and diabetes.
The study, published in the journal Nutrition, finds that the Taq1 A1 gene, a variant that results in fewer dopamine receptors on brain cells, is surprisingly widespread among individuals with type 2 diabetes. Dopamine is a brain chemical associated with pleasure.
People with the A1 variant get less than the normal amount of dopamine stimulation and tend to compensate with self-stimulatory behavior, such as smoking, drinking, gambling, and overeating. In this clinical trial of 93 adults with type 2 diabetes, the A1 gene was identified in about half the participants. In some groups, the prevalence was similar to that observed in substance-abusing populations. Dr. Barnard speculates that, for affected people, a lack of dopamine receptors leads to overeating and weight gain. In turn, weight gain leads to diabetes.
Half the people in this study were on a low-fat vegan diet, and half followed the standard American Diabetes Association diet, which has strict portion controls. Dr. Barnard found that those who did not have the A1 gene did dramatically better on the vegan diet, compared with those on the standard diabetes diet. Those with the A1 gene got poorer results on both diets, although they did slightly better on the vegan diet.
This shows that, for many people, it is easier to simply leave problem foods aside instead of trying to moderate their intake. It also suggests that, for some people, foods have an attraction similar to that of habit-forming drugs.