Scientists have found more than 30 new gene variations linked to obesity and fat in research they say could help explain why some people get so overweight, and why some are apple shaped and some shaped like pears.
An international team of more than 400 scientists from 280 research institutions said their results give more insight into the biological processes that can lead to obesity and may in future help in developing new ways to treat or prevent it.
But they said that while genes do play a role in obesity and weight problems, they stressed that they account for only a fraction of the reason people are overweight with the main culprits being a bad diet and lack of exercise.
"We should not forget that, while the genetic contribution to obesity is substantial, a large part of obesity susceptibility remains down to our lifestyle," said Ruth Loos of the Medical Research Council's Epidemiology Unit in Cambridge, who also worked on the research.
In the first of two studies published in the journal Nature Genetics Sunday, the scientists identified 13 new gene regions where variations in DNA sequence can be linked to whether a person is are apple-shaped or pear-shaped.
Most of these variations have a markedly stronger effect in women than in men, they said.
Apples and Pears
Previous studies have found that where we store fat in our bodies can affect our health. More fat around the waist -- being apple-shaped -- is linked with an increased risk of type 2 diabetes and heart disease, while having a fat bum and thighs -- being pear-shaped -- has been suggested in some research to offer some protection against diabetes and high blood pressure.
"By finding genes that have an important role in influencing whether we are apple-shaped or pear-shaped, and the ways in which that differs between men and women, we hope to home in on the crucial underlying biological processes," said Cecilia Lindgren of Oxford University, who worked on both studies.
"As efforts to tackle obesity through changes in lifestyle or by different treatment options have proved extremely challenging, the potential to alter patterns of fat distribution may offer an alternative for future drug discovery."
The second study looked for genes connected to body mass index (BMI) -- a weight-to-height ratio measure used to classify whether adults are overweight or obese. A BMI of between 25 and 30 is overweight and a BMI of 30 or over is obese.
Using almost 250,000 people in a genome wide association study -- which involves scanning entire gene maps for DNA clues -- the researchers found 18 new genetic regions linked to BMI, more than doubling the DNA variations found so far to 32.
Some of the new findings suggest the involvement of genes active in the brain that influence appetite, they said, and some suggest genes involved in controlling insulin and metabolism.
The study also found that people who inherit many of the BMI-increasing DNA variants from their parents weigh between seven and in kilograms more than those who inherit few of the variants. This difference in weight is solely due to the fact that they differ genetically, the scientists wrote.
"These two studies are the beginning of new insights into to biology of obesity and body shape, which in turn may lead to more targeted approaches to obesity prevention and potentially to the development of new drugs," Loos said.