The largest-ever study of the human genome to date has yielded the strongest evidence of a genetic basis for obesity, scientists say.

Researchers with the international Genetic Investigation of Anthropometric Traits Consortium, analyzing genetic samples from more than 300,000 individuals, report finding more than 140 locations across the genome that play roles in various obesity traits.

The findings can help clarify why some people are more likely than others to add extra weight and develop conditions linked to obesity, the researchers report in two papers published in the journal Nature.

One of the studies looked for a genetic basis for where fat is stored in and around the body, researchers said.

"We need to know these genetic locations because different fat deposits pose different health risks," says senior author Karen Mohlke, a professor of genetics at the University of North Carolina School of Medicine.

People with excess fat around the abdomen face more health concerns such as diabetes and cardiovascular disease than whose fat is carried mostly around the thighs, the researchers say.

Around 30 of the newly discovered genome regions are linked to the distribution of body fat, they found.

A second study examined the association between genes and body mass index or BMI, a measure of body fat based on a person's height versus their weight.

Almost 100 genetic locations proved to be linked BMI, the scientists found, and were also linked to factors such as energy use and appetite.

The finding that genetic regions linked to obesity also have links to our nervous systems came as a surprise, says Dr. Elizabeth Speliotes, a University of Michigan Health System researcher and senior author of the BMI paper.

"You don't go to your neurologist to discuss your weight -- when we think about obesity we don't generally think of the nervous system.

"But this changes the way we think about obesity -- rather than just a metabolic condition perhaps it has a neurological basis too," she says.

The sheer number of genetic regions linked to obesity means there's a lot of work ahead to understand why and how people gain weight, she adds.

"Our work clearly shows that predisposition to obesity and increased BMI is not due to a single gene or genetic change.

"The large number of genes makes it less likely that one solution to beat obesity will work for everyone, and opens the door to possible ways we could use genetic clues to help defeat obesity," she says.

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