It's no secret that a combination of greasy fast food and couch potatolike behavior has contributed to America's obesity epidemic.
Many scientists, however, have also wondered whether something else is involved: Could there also be a genetic explanation?
Research is showing this may indeed be the case for some people. In today's issue of the journal Science, researchers explain how they have found a variation, or "misspelling," of DNA located near a gene that normally affects fat metabolism.
"It's the first common genetic variant to be associated with obesity," said Dr. Michael Christman, a lead researcher and chair of the Department for Genetics and Genomics at Boston University.
DNA contains genetic material, or instructions, for cells throughout the body. Genes are pieces of DNA that carry out these instructions.
Researchers discovered this variation after analyzing DNA samples collected from 9,881 people over a 24-year span. They also discovered that people of different racial, ethnic and age groups who had the same misspelling had an increased risk of obesity.
"The strength of this study was that we were able to replicate the data in different populations," said Dr. Alan Herbert, a lead researcher of the study and assistant professor of genetics and genomics at Boston University.
Ten percent of the population has this misspelled DNA, scientists estimate, and those who have it also have a 30 percent to 50 percent increased risk of becoming obese.
Obesity is considered a risk factor for a number of diseases such as hypertension, diabetes and stroke. In recent years, obesity rates have increased drastically in both adults and children.
The study could lead to a better understanding of what role genetics plays in obesity.
"We have not understood what the common genes are that predispose us to the disease," Christman said.
Genetic researcher Dr. Teri Manolio, of the National Human Genome Research Institute, said the study was one of the best she'd seen on the topic.
"It followed people for so long and so carefully … studied family associations but also studied unrelated people. … The results weren't a fluke," Manolio said.
The researchers hope that the findings will have an impact on other scientific research and on how pharmaceutical companies design drugs.
"It's like finding another piece in the puzzle. … Eventually we'll see the whole picture," said Nan Laird, a co-author of the study and professor of biostatics at the Harvard School of Public Health.
Even with more research, scientists caution about relying solely on genetics to explain a few extra pounds.
"It's not for us to think, 'Obesity is in your genes -- there's nothing you can do about it,'" Manolio said.
"We need to pay more attention to increasing physical activity and moderating dietary intake," she said.
Dr. Jennifer Caudle is an intern at Delaware County Memorial Hospital in Drexel Hill, Pa. Caudle plans to specialize in family practice.