Secrets of your jean size may be all in the genes
Scientists have found more than 30 new gene variations linked to obesity and fat in research they say could help explain why some people become so overweight.
The research could hold the secret as to why some people are apple-shaped and other are shaped like pears.
An international team of more than 400 scientists from 280 research institutions said their results gave more insight into the biological processes that can lead to obesity and may in the future help in developing new ways to treat or prevent it.
But they said that while genes did play a role in obesity and weight problems, they stressed that they accounted for only a fraction of the reason people were 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' yesterday, the scientists identified 13 new gene regions where variations in DNA sequence can be linked to whether a person is apple-shaped or pear-shaped.
Most of these variations had a markedly stronger effect in women than in men, they said.
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 in England, 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 more is obese.
Using almost 250,000 people in a genome wide association study -- which involved 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 suggested the involvement of genes active in the brain that influenced appetite, they said, and some suggested 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 at least seven kilograms more than those who inherit few of the variants. This difference in weight was solely due to the fact that they differed genetically, the scientists wrote.
"These two studies are the beginning of new insights into the 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," Ms Loos said.