A “thrifty” gene that may have once protected Samoans in times of food scarcity could now be contributing to their record-high rates of obesity, a new study reports.
In a paper published in Nature Genetics, a team of scientists including Yale School of Public Health researcher Nicola Hawley, Ph.D., assistant professor in the Department of Chronic Disease Epidemiology, links a gene variant, common in the local population but rare in the rest of the world, with a higher body mass index (BMI).
While obesity is reaching pandemic levels world wide, the problem is of acute concern in the South Pacific Island of Samoa, where 80 percent of men and 91 percent of women are obese, and BMI has reportedly risen at five times the global rate over the past 30 years.
To find the gene related to higher BMI, the research team genotyped more than 600,000 markers on the genomes of more than 3,000 Samoans from 33 villages across Samoa. On chromosome five, they were able to pinpoint a mutation as the variant associated with a substantially increased risk of obesity when present. This variant, while common in Samoans, is virtually nonexistent in other populations and has an effect size much larger than other known obesity risk variants. Interestingly, while the mutation increases risk of obesity, it simultaneously appears to protect against diabetes risk.
“This is a fascinating finding,” said Hawley, one of the paper’s first authors. “We have more work to do to understand how this mutation really exerts it effect, but we hope that with that understanding we may be able to develop much better interventions for use in the Samoan setting.”
On chromosome five, [the researchers] were able to pinpoint a mutation as the variant associated with a substantially increased risk of obesity when present.
While the gene is a strong indicator of a genetic cause for obesity, it is just one of many factors that contribute to Samoa’s record rates of obesity. In her previous research, Hawley outlined the environmental factors that have exacerbated the obesity crisis there, including greater consumption of processed foods and more sedentary lifestyles.
Because Samoans historically did not always exhibit such a high level of obesity, it is possible, researchers suppose, that Samoans who carried this “thrifty” gene at the time of the first settlement of the islands were better able extract and store nutrition from limited food resources. Now, the gene that contributed to survival in a time of food scarcity has the opposite effect, increasing BMI in an environment dominated by an abundance of unhealthy, high-calorie foods.
The relative isolation of the Samoan population, located in the South Pacific, provides researchers with an opportunity to study the genetic causes of obesity, with the future potential to apply their findings to other populations around the world. More research is needed to gain deeper knowledge of the evolutionary roots of obesity, so that policymakers can make more informed decisions in Samoa about how to address their obesity-related health challenges.
Hawley collaborated on the research with scientists from the United States (Brown, Pittsburgh, and Cincinnati Universities), Samoa and American Samoa.