High rates of obesity among Samoans partly attributed to genetics

A study reports that a genetic variant that affects energy metabolism and fat storage partly explains why Samoans have among the world’s highest levels of obesity.


The report by Stephen McGarvey, corresponding author of the paper in Nature Genetics and professor in the Brown University School of Public Health in the US, suggests nearly half of Samoans have a newly identified and significant genetic variant that contributes to obesity risk.


A recent phenomenon said to be influenced by the globe’s rapid shift to calorie-rich, processed foods and more sedentary lifestyles, the high rates of obesity could actually be linked to genetics.


This remained undiscovered until researchers focused on the islands’ populations.


In cell models in the lab, this “thrifty” variant promoted more efficient storage of more fat.


“A previously unknown genetic variant in an understudied gene is strongly associated with body-mass index (BMI) levels and other adiposity measures in Samoan men and women we studied in 2010,” says Stephen McGarvey.


While the variant helps to explain why 80% of Samoan men and 91% of women were overweight or obese, he says it is by no means a dominant factor.


“Although we have found a genetic variant with a reasonable biological mechanism, this genetic variant is just one part of the many reasons for the high levels of BMI and obesity among Samoans.”


The gene gives you a 35 percent higher chance of being overweight - however scientists say factors like diet and exercise are still important.


McGarvey, with a team of colleagues at the University of Pittsburgh, Cincinnati and Yale, conducted the study with Samoan government officials.


The team pinpointed a single genetic variant on chromosome 5 that, according to the researchers’ estimate, is associated with about 35% higher odds of being obese compared to not having the gene variant.


In several independent samples of people from the islands, totaling more than 5000 individuals studied since the 1990s, 7% of volunteers had two copies of the mutation and another 38% had one copy.


Those with it were more likely to have a higher BMI than those who don’t.


At the same time, those with the variant were less likely to have developed Type 2 diabetes.


Nevertheless, Samoans also have among the world’s highest rates of that condition.


The variant is virtually nonexistent in African and European populations and at a low frequency among East Asians.