Studies Find Genetic Link to Obesity

Two recent studies with ties to Harvard Medical School have discovered new genetic variations that predispose people to obesity and affect general fat distribution within the human body.

The studies examined 32 genetic obesity susceptibility loci, 18 of which were new to the researchers.

Joel N. Hirschhorn ’86, associate professor at the Medical School and senior associate member and coordinator of the Metabolism Initiative at the Broad Institute, and Elizabeth K. Speliotes, an instructor in medicine at Massachusetts General Hospital and the Broad Institute, worked with hundreds of other researchers as part of the Genetic Investigation of Anthropometric Traits (GIANT) consortium beginning in 2007 to isolate specific genetic arrangements that might predict a person’s likeliness to be obese.

The researchers investigated the possibility that these genetic variations might determine a person’s Body Mass Index, a measurement of body density that scientists and researchers use to gauge obesity.

The study on Body Mass Index was conducted on a sample size of over 249,796 individuals, while the second one on fat retention was conducted on 190,803 people.

The benefit of working in a consortium was that the researchers were able to accumulate a significant body of knowledge on a topic they believed may prove valuable but had little supporting data, according to Speliotes.

In their study of fat distribution throughout the body, the researchers used the waist-to-hip ratio of men and women to examine the gender differences in bodily adiposity and the metabolic effect of different types of fat.

“Fat is not homogeneous throughout the body,” said Lee M. Kaplan ’75, associate professor of medicine and director of the MGH Obesity Research Center. “Fat around the abdomen is associated with metabolic disorders such as heart diseases while subcutaneous fat just under the skin sometimes has a protective function.”

Speliotes said that the studies have important policy implications.

“Through work like this, it opens up a lot of areas into possible research that could better classify types of obesity and could offer better care for obesity in the future,” she said.

Speliotes added that there are similar health care implications for the second study about fat retention throughout the body, which she said might lead to more adequate and patient-specific care options—such as individually tailored diet plans and the development of new drugs—that might help combat the U.S. obesity epidemic in the future.