American scientists have shown that adults too have a type of "good" fat that is generally thought to be present only in babies and children.
Researchers at the Joslin Diabetes Center in Boston, Massachusetts, point out that this good fat, also known as brown fat, is active in burning calories and using energy.
They believe that their finding may pave the way for new treatments both for obesity and type 2 diabetes.
While scientists have always believed that brown fat is mostly gone by adulthood, the new study has for the first time shown it to be present and metabolically active in adult humans.
"The fact that there is active brown fat in adult humans means this is now a new and important target for the treatment of obesity and type 2 diabetes," said Dr. C. Ronald Kahn, senior author and Head of the Joslin Section on Obesity and Hormone Action and the Mary K. Iacocca Professor of Medicine at Harvard Medical School.
According to the researchers, the idea behind a new therapy would be to find a way to stimulate brown fat growth to both control weight and improve glucose metabolism.
"Not only did we find active brown fat in adult humans, we found important differences in the amount of brown fat based on a variety of factors such as age, glucose levels and, most importantly, level of obesity," said lead author Dr. Aaron Cypess, a Research Associate and Staff Physician at Joslin.
The study revealed that younger patients were more likely to have larger amounts of brown fat, and that the good fat was more active during colder weather, keeping with its role of burning energy to generate heat.
Brown fat was also found to be more common in adults who were thin, and had normal blood glucose levels.
"What is of particular interest is that individuals who were overweight or obese as measured by higher Body Mass Index (BMI) were less likely to have substantial amounts of brown fat," said Kahn.
"Likewise, patients taking beta-blockers and patients who were older were also less likely to have active brown fat. For example, individuals both over age 64 and with high BMI scores were six times less likely to have substantial amounts of brown fat," Kahn added.
The researchers say that their findings suggest a potential role for brown fat in regulating body weight metabolism, suggesting that its higher levels may protect against age-related obesity.
They are hopeful that an increased ability to measure brown fat mass and activity in vivo in humans will lead to a better understanding of its role in physiology, and its potential as a target for therapy of obesity and other metabolic disorders.
During the study, the researchers analysed a database of 1,972 patients who had undergone positron emission tomography/computed tomography (PET/CT) scans for a variety of reasons over a three-year period.
The team found substantial brown fat deposits in 7.5 percent of the female patients, and over 3 percent of males.
Dr. Kahn revealed that most of the deposits found on the scans were located in the neck region.
"In the real world, there has been a long debate as to whether brown fat exists in adult humans and whether it was important physiologically," he said.
"This study demonstrates that it is both present and appears to be physiologically important in terms of body weight and glucose metabolism. We hope this opens up a new therapeutic area for obesity and type 2 diabetes by modifying the activity of brown fat," he added.
A research article on this study has been published in the New England Journal of Medicine.