Scientist have discovered a gene that makes people more likely to absorb fat.
The discovery could help understand fat absorption
They were looking at why some people are more prone to diseases linked to excessive consumption of fat.
But they say it may help understand how too much fat can lead to obesity, diabetes, high blood fat levels and heart attacks.
It may and aid the development of new treatments.
An international team of researchers looked at the genetic causes of severe fat malabsorption in three rare diseases, chylomicron retention disease (CMRD), Anderson Disease and CMRD with Marinesco Sjogren syndrome, a neuromuscular disorder.
The genetic mutations in the three disorders mean that a protein called Sar1b, which is required for all dietary fat absorption, cannot work properly.
This opens up exciting new avenues for understanding of the origins of obesity
Professor James Scott, Imperial College
Scientists from Imperial College London and the Hammersmith Hospital studied families from across the world and found all those affected by the three disorders had the same genetic mutation.
Imperial College researchers then showed how the mutations caused CMRD and Anderson Disease, preventing a specific activity of Sar1b.
Those patients who have both CMRD and Marinesco Sjogren syndrome, have the neuromuscular problem because they do not have the Sar1b protein at all.
Dr Carol Shoulders, of the Medical Research Council Clinical Sciences Centre at Imperial, said: "Further studies will focus on whether people with genetic variations in Sar1b absorb more dietary fat, and are therefore more prone to those diseases associated with excessive consumption of fat.
"These results are expected to provide new therapeutic ways for controlling diet-induced obesity and high blood cholesterol levels."
Professor James Scott of Imperial's Genetics and Genomics Research Institute said:"This opens up exciting new avenues for understanding of the origins of obesity, and in the long term may open up new avenues for treatment of this most serious of modern diseases."
Dr Ian Campbell, chairman of the National Obesity Forum, told BBC News Online: "There is so much we need to learn about weight regulation.
"Any discovery which adds to our knowledge of how we gain and lose weight may help us to influence the process."