Scientists in the United States say people who hang on to their baby fat may be protected from developing type 2 diabetes and becoming obese - obesity is a major risk factor for type 2 diabetes.
Fat it seems can be good as well as bad and this depends on the type of fat - common white fat is bad because it stores energy, whereas brown fat, found most abundantly in babies and children, is active in burning calories and using energy - it generates heat and keeps the body warm.
Babies are unable to shiver when cold and the brown fat burns calories to make heat; women appear to have more of it than men and it was also more common in adults who were thin and had normal blood glucose levels.
Scientists believe most adults have some brown fat, but how much a person has depends on a number of factors, including age, glucose levels and body weight.
Scientists at Harvard Medical School have found that not only do adults still have brown fat, but that slim adults had more of it than fatter ones.
According to the research team at the Joslin Diabetes Center, it may be possible in the future to stimulate brown fat growth to control weight and improve glucose metabolism, thereby preventing obesity and type 2 diabetes.
In a study led by Professor Ronald Kahn of nearly 2,000 patients, signs suggestive of brown fat deposits on routine medical scans were found in 7.5% of the women and 3% of the men investigated.
In order to confirm their findings the researchers then identified 33 other patients whose pathology records had indicated the presence of brown fat in their necks - the same place where the PET/CT scans had identified the largest concentrations of brown fat.
When the tissue of two of those patients was tested the presence of a special heat-generating protein called UCP-1 was detected which is unique to brown fat.
Although the numbers with brown fat in the study were small, the scientists believe this represents an underestimate, since medical scans could easily miss smaller and less active brown fat deposits.
The study also revealed that younger people were more likely to have larger amounts of brown fat and the brown fat was more active during colder weather, in keeping with its role of burning energy to generate heat.
Professor Kahn says it was interesting that individuals who were overweight or obese were less likely to have substantial amounts of brown fat as were patients taking beta-blockers and patients who were older.
The researchers say that brown fat not only exists in adult humans, but is also metabolically active and they suggest that brown fat plays an important role in regulating body weight and that higher levels of brown fat may protect against obesity.
Professor Kahn says there has been a long debate as to whether brown fat exists in adult humans and whether it was important physiologically and the study demonstrates that it is both present and appears to be physiologically important in terms of body weight and glucose metabolism.
Professor Kahn says they hope this opens up a new therapeutic area for obesity and type 2 diabetes by modifying the activity of brown fat. Professor Kahn's team has already shown that a protein, BMP-7, known for its role in inducing bone growth, can also help promote the development of brown fat in rodents.
The research is published in the New England Journal of Medicine.