Different genetic causes for obesity have been identified, raising the possibility of tailored treatments for patients.
Obesity could be 'caused' by genetic conditions
US researchers found different genes were responsible for obesity in different groups of mice.
This could allow scientists to tailor different treatments for people who perhaps have a metabolic problem, and those whose bodies have flawed hunger message signals, meaning they eat too much.
Scientists from US companies Rosetta Inpharmatics and Merck and the University College of Los Angeles, examined obesity in genetically altered mice.
They used sophisticated techniques to discover which genes were turned on and off and which parts of the mice's genetic make-up were different.
The more we understand about obesity, the less it seems to be the patient's fault
Dr Ian Campbell, National Obesity Forum
All mice were on high-fat diets, but some did not put on weight, while others did.
It was found that overweight mice could be divided into two distinct genetic types.
Scientists also found a "hotspot"' of obesity-related genes on chromosome 2.
Dr Eric Schadt, who led the research, told BBC News Online: "While the end result is the same, in that you get obese, the reasons why you get obese are varied, and genetically controlled."
He said it was not yet possible to understand the details of the differences between the two mice groups.
"We were able to put them into different groups and identify the patterns of genes going on and off."
He added: "When we start to look at the treatment of the disease, understanding these specific sub-types of the disease is very important.
"It might be that the treatments vary between the different subtypes.
"You could have one sub-type of people who are obese because of a gene that affects hunger perception.
"Another group might have a defect in their metabolic rate."
Genes and the environment
Dr Ian Campbell, chair of the UK's National Obesity Forum, told BBC News Online: "Our understanding of obesity is growing all the time.
"Some of the discoveries in the field of genetics are opening up possibilities of a whole new range of treatments."
He added: "The more we understand about obesity, the less it seems to be the patient's fault.
"It's more a combination of genetic and environmental influences."
The research is published in Nature.