'Bad' fat can convert to 'good' fat and vice-versa

Scientists have shown for the first time that brown and white fat cells in a living organism can be converted from one cell type to the other, paving way for development of new anti-obesity therapies.
The work, by scientists from ETH Zurich, Switzerland, provides important new insights into the origin of brown fat cells.
Two types of fat cells can be found in mammals and hence in humans: White fat cells function mainly as highly flexible energy stores which are filled in times of calorie abundance.
The fat is stored in the form of lipid droplets, which are mobilised when energy is needed. Diametrically opposed in function are the so-called brown adipocytes: These cells specialise in burning energy in the form of fat and sugar to produce heat.

New-born babies possess substantial amounts of brown fat and utilise it to maintain body temperature. Since it was recently shown that brown adipocytes also exist in adult humans, research has focused on understanding how brown adipocytes are formed.
The ultimate goal of these efforts is to increase brown adipocyte number and activity in obese humans, allowing them to burn excess calories and thus reduce weight.

It is known that both humans and mice can adapt to cold temperatures by forming brown fat cells within their white fat depots. These cells are called "brite" fat cells (brown-in-white) and are less common at warmer versus colder temperatures.

However, the origin of these special brown adipocytes has remained a matter of debate. The prevalent hypothesis was that brite cells are formed from special precursor cells and are removed when no longer needed.
The alternate idea of a direct interconversion between white and brown fat cells gained less attention. By demonstrating that this interconversion does occur and is one of the main contributors to brite fat cell formation, the current belief has been challenged.
To demonstrate how brite fat cells are formed the researchers in the laboratory of Christian Wolfrum, a professor at the Institute of Food, Nutrition and Health, generated mice that allowed them to genetically label specific fat cells.

These animals were kept in a changing environment: starting at 8 Degree C for a week and for several weeks afterwards at normal room temperature.
During the cold exposure, the mice formed brown adipocytes in their white fat depots - a process called "britening".
After warm adaptation the fat tissue turned white again. Using the genetic markers the scientists concluded from these experiments that white fat cells can convert into brown fat cells and vice versa.
As humans have the same type of cells as mice it is likely that the same process occurs in humans upon cold stimulation.
"To develop new treatment strategies we need to find ways to convert white into brown adipocytes," said Wolfrum.