Researchers at the Joslin Diabetes Center have demonstrated that adult humans still have a type of “good” fat previously believed to be present only in babies and children.
Unlike white fat, which stores energy and comprises most body fat, this good fat, called brown fat, is active in burning calories and using energy.
The finding, reported in the April 9th issue of The New England Journal of Medicine, could pave the way for new treatments both for obesity and type 2 diabetes.
Scientists had thought that brown fat only existed in humans during childhood and was mostly gone by adulthood. The paper shows that brown fat not only exists in adult humans, but also for the first time, that the fat is metabolically active.
Obesity is a major risk factor for type 2 diabetes. 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 Aaron Cypess, M.D., Ph.D., a Research Associate and Staff Physician at Joslin.
Not surprisingly, the study found that younger patients were more likely to have larger amounts of brown fat, and the brown fat was more active during colder weather, keeping with its role of burning energy to generate heat. Brown fat was also 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.”
The findings, particularly those having to do with BMI, suggest a potential role for brown fat in regulating body weight metabolism, the paper says, suggesting that higher levels of brown fat may protect against age-related obesity.
“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,” Dr. Kahn 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.”
The current study was supported by the Clinical Investigator Training Program, Beth Israel Deaconess Medical Center – Harvard/MIT Health Sciences and Technology, in collaboration with Pfizer Inc. and Merck & Co.; as well as with grants from the National Institutes of Health and the Eli Lilly Foundation.
Source: Joslin Diabetes Center, USA