But the researchers who spotted that gene variant stop short of chalking obesity up to genetics. At this point, they just report an "association" between the gene variant and obesity.
In other words, the scientists found the gene variant among obese people. But it's not clear if those people would have been slimmer without the gene variant.
The study, published in Science, comes from researchers including Alan Herbert, M.BChB., Ph.D., of the genetics and genomics department at Boston University's medical school.
Probing the Genes
Herbert's team focused on genetics and body mass index (BMI) in five large groups of people.
First, the researchers checked the DNA and BMI of nearly 700 people whose parents had participated in the Framingham Heart Study, a long-term study of heart health among people in Framingham, Mass.
Herbert's team found that when two copies of a particular gene variant were present, people had a higher BMI and were more likely to be obese. BMI is based on height and weight. A BMI of 30 or more is considered obese and a BMI of 25 or more is considered overweight.
But the researchers didn't stop there. They wanted to see if the same gene variant cropped up in other studies of obesity, or if their finding had been a fluke.
The researchers repeated their analysis in four other groups, including almost 4,000 people of Western European ancestry, more than 2,600 whites from Poland and the United States, nearly 900 blacks living in Maywood, Ill., and more than 2,700 participants in the long-term Nurses Health Study.
The same gene variant was linked to obesity in three of those four groups, prompting the researchers to note a "consistent association" between the gene variant and obesity.
The exception was the Nurses Health Study, which didn't show the same pattern. Those participants may have had "a different BMI distribution … or differences in environment and lifestyle," write Herbert and colleagues.
How Common Is the Gene Variant?
Ten percent of people have this particular gene variant pattern, Herbert and colleagues write.
If their estimate is correct, it doesn't account for all obesity. Among U.S. adults, 32 percent are obese and 70 percent are overweight or obese, the CDC recently reported.
Other gene variants are probably also associated with obesity, Herbert's team notes. The gene variant they tracked is located near the INSIG2 gene, which is involved in fat metabolism and has been studied as a possible influence on obesity in mice and humans.
What about diet and exercise? Those topics weren't part of Herbert's study, so there's no proof that participants' obesity was solely due to the gene variant.
SOURCES: Herbert, A. Science, April 14, 2006; Vol. 312: pp. 279-283. WebMD Medical News: "Obesity Epidemic Balloons to New Girth." News release, Science. News release, Harvard School of Public Health.
By Miranda Hitti
Reviewed By Ann Edmundson, M.D.
© 2005, WebMD Inc. All rights reserved