For years, researchers assumed that fat was an inert, unresponsive tissue that didn't do much other than to serve as a source of energy for cells. But it turns out that fat is actually quite active, releasing all kinds of chemicals and agents and signaling molecules that affect the way the body utilizes and stores calories. Understanding how such fat cells change the body's metabolism could lead to more targeted treatments not just for obesity but for some of the health problems such as diabetes and heart disease that occur as a result of it.
Fat cells are, for example, replete with macrophages, the immune cells that engulf foreign invaders and put the body's other defensive cells into attack mode. For some reason, macrophages become hyperactive inside the fat cells of obese people, sending out signals to recruit other inflammatory factors. The result of all the commotion is an inflammatory response that is known to raise the risk of heart disease and diabetes associated with obesity.
That's what researchers found when they infused healthy individuals with an emulsion of fatty acids — which are normally released into the bloodstream when fat cells are broken down for energy. (Obese people have more fatty acids, since they have more fat.) After five hours of receiving the fat solution in their blood — up to levels of an obese person with diabetes — the healthy volunteers became less sensitive to insulin, which is exactly what happens to overweight individuals on their way to developing diabetes.
It seems that free fatty acids may be the reason stored fat cells send out inflammatory signals. "What is exciting for us is we can understand the exact processes behind what these fat cells are doing, we can use more targeted medications to treat the consequences of obesity," says Dr. Preeti Kishore, the lead researcher on the study at Albert Einstein College of Medicine.