New research shows how adipocytes, or fat cells, regulate the flow of fat in and out of the cells. Although excess fat is the bane of bodybuilders, fat does serve a few vital physiological functions in the body. For example, when the body is at rest, about 80 to 90 percent of the
energy required by cardiac and skeletal muscle comes from fat. The body has only limited storage space for carbohydrates in the form of liver and muscle glycogen.
In addition, glycogen is stored with 2.7 grams of water per gram of glycogen, whereas Tat is essentially water-free, so the body has a far greater capacity for fat storage.
Fat cells apparently monitor and adjust their own fat content through what's caned the adipsin-ASP pathway. Among other functions ASP promotes glucose entry into the lit cell in a manner similar to that of insulin. It also increases the activity of a fat cell enzyme that regulates
the attachment of fatty acids to a glycerol molecule to form triglycerides, the stored form of fat.
The most potent food stimulus to ASP production in fat cells is dietary fat. The more fat you eat, the greater the production of ASP. This explains why dietary fat is far more fattening than either carbohydrates or protein, neither of which appreciably affects ASP.
While this appears to be a negative aspect of metabolism, ASP takes over the uptake of fat from the blood when the fat cell enzyme, lipoprotein lipase, is overloaded. This function is important for health because fat cells act as sinks for excess fat and glucose circulating in the
blood. If these excess nutrients aren't soaked up by the sponge like fat cells, they continue to circulate and eventually convert into substances that promote cardiovascular disease.
When you diet and lose weight, ASP activity decreases and your body is able to release stored fat and use it for energy instead of protein. Thus, ASP produces a catabolic function in the body by favoring the use of protein, or muscle, over fat as an energy source. As your fat cells
shrink from dieting, however, ASP activity downgrades and protein is spared.
