'Good' Energy Burning Fat In Lean Adults
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
New England Journal of Medicine, could pave the way for new treatments
both for obesity and type 2 diabetes.
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
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.
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.
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 scoreswere six times less likely to have substantial
amounts of brown fat."
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
the paper, the researchers 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.
This study answered those questions thanks to the use of modern imaging technology.
researchers analyzed 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. They identified
substantial brown fat deposits in 7.5 percent of the female patients
and over 3 percent of males.
numbers clearly represent an underestimate, since PET/CT can only
detect collections of brown fat cells of a certain size and activity,
and could miss smaller and less active deposits," Kahn explained.
the researchers identified 33 other patients whose pathology records
had indicated the presence of brown fat in their necks in the same
places where the PET/CT scans had identified the largest concentrations
of brown fat. They tested the tissue of two of those patients and
detected the presence of a special heat-generating protein called UCP-1
that is unique to brown fat.
"These findings suggest that there is previously unrecognized, heat-generating brown fat in many adults," Dr. Cypess said.
by demonstrating the presence and physiological activity of brown fat
in adult humans, shows that this tissue may provide a novel and
valuable target for interventions, pharmacological and environmental,
to modulate energy expenditure," said Francesco Celi, M.D., of the
Clinical Endocrinology Branch, National Institute of Diabetes and
Digestive and Kidney Diseases, National Institutes of Health, who wrote
an accompanying editorial but was not involved in the Joslin study.
Dr. Kahn said
there is a good possibility that brown fat may be present in
significant amounts in much higher percent of the population, but that
it may be more spread out and not as easily seen on imaging in many
cases. Most of the deposits found on the scans were located in the neck
"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
glucosemetabolism. We hope this opens up a new therapeutic area for
obesity and type 2 diabetes by modifying the activity of brown fat."
For more information on the Joslin Diabetes Center, visit www.joslin.org.