Feb 6, 2009

Science - Fat cells help weight reduction

WASHINGTON: Georgia State University researchers have discovered that fat cells in the body work in the same fashion as a thermostat regulates
temperature inside a house—giving feedback to the brain to regulate the process of fat burning. C. Kay Song and Tim Bartness, who conducted this study in collaboration with Gary J. Schwartz of the Albert Einstein College of Medicine, say that their work may help advance the scientific understanding of how weight is shed. The researchers found that during the process of burning fat, known as lipolysis, fat cells use sensory nerves to feed information to the brain. The team revealed that they used viruses to trace communications in the nerves of Siberian hamsters, and found that the brain uses part of the nervous system used to regulate body functions, called the sympathetic nervous system, to in turn communicate back to the cells to initiate, continue or stop the fat burning depending upon the information the brain receives from the fat. "The brain can trigger lipid burning by fat cells and through these sensory nerves, the fat cell can give the brain feedback. This is a really important concept in biology, as it can regulate the process of lipolysis much like how a thermostat regulates temperature in your house, using input from the air and output to a furnace or heating unit," Bartness said. "The presence and function of the sensory nerves has been completely ignored and the areas in the brain that receive this sensory information were unknown until we did these studies," he added. When the body has a low amount of a carbohydrate called glycogen, which acts as fuel for lipolysis, the body starts this process to release energy stored in fats. Finally, nerves that are part of the sympathetic nervous system, a chemical called nor epinephrine are released to trigger the breakdown of fat. Bartness says that sensory nerves later inform the brain about the status of the lipolysis, communicating whether too much or too little energy has been released – and the activity of the sympathetic nerves can be adjusted accordingly. "If you're doing a moderate amount of exercise or even if it has been a fairly long interval since you last ate, you will use up all or most of the available glycogen, necessitating the break down fat to yield sufficient energy. But you don't want to break down more than you need. So, this would be a way to stop the sympathetic nervous system from triggering the release of too much lipid energy from fat," he said. According to the researchers, though this communication process is known to play a role in the short-term burning of fat, it has yet to be determined whether this process is involved with the long-term issues of burning fat – important in understanding obesity and why some people burn fat more readily than others. "It could be that sensory nerves have a dual function. In addition to the moment-to-moment lipolysis process, they might also have a longer term function. It's complicated, and it might be a different subset of the sensory nerves performing the long-term monitoring of fat reserves," he said.