( BBC ) Measuring levels of a protein in the blood could provide the most accurate way to assess how much fat coats the body's organs, say scientists.
The build-up of visceral fat has been linked to an increased risk of heart disease and type 2 diabetes.
The researchers found a specific protein is produced in much greater amounts by visceral fat than fat that lies just beneath the skin.
The study, by a US and German team, appears in the journal Cell Metabolism.
The researchers, from Harvard University and the University of Leipzig, analysed 196 people.
They showed the genes which produce the protein - RBP4 - were up to 60 times more active in obese people with high levels of visceral fat than in lean people.
In contrast, the same genes were only 12 times more active in obese people with a preponderance of fat lying just under the skin.
Cutting levels
The researchers believe that measuring RBP4 would potentially be an effective way to assess body fat, and that treatment to cut levels of the protein might also have health benefits.
In previous work, they showed that cutting RBP4 levels in obese mice helped the animals to make better use of the hormone insulin - and thus reduce their risk of diabetes.
They also showed that measures to improve insulin sensitivity in human subjects resulted in a drop in RPB4 levels.
Researcher Dr Matthias Bluher said: "We believe that in the near future, measurements of RBP4 serum concentrations might serve as a novel biomarker for visceral obesity and increased risk for type 2 diabetes and other adverse outcomes of visceral obesity.
"In addition, pharmacological interventions that reduce RBP4 levels might be a new approach in the treatment of metabolic syndrome and visceral obesity."
The only known function of RBP4 is to carry vitamin A in the blood.
Dr Iain Frame, research manager at Diabetes UK, said the research was interesting, but much more work was needed before it would be possible to draw conclusions about the feasibility of a blood test.
He said: "While we welcome innovations which could help identify people at risk, at present a quick and easy way to measure the risk of Type 2 diabetes is by measuring waistlines."
A waist measurement of 37 inches (94cm) or more for men, and 31.5 inches (80cm) or more for a woman is considered to raise the risk.
For men of South Asian origin a waist measurement of 35 inches (89cm) or more is considered a risk.
June Davison, a cardiac nurse at the British Heart Foundation, agreed that more research was needed to draw firm conclusions.
She said: "What we know for certain is that being overweight or obese increases your risk of developing heart disease and having a heart attack.
"That's why we encourage people to take steps to control their weight, shrink their waistlines, and reduce their risk by eating a healthy balanced diet and being physically active."