Fat transfer is a very common procedure to enhance any part of the body. As a matter of fact, fat transfer is becoming an essential component of any plastic surgery, including the face and body, among other areas. But how does fat transfer work? You have noticed that many times when we talk about fat transfer to the buttocks, surgeons recommend you not to sit for about two weeks, but what is it? The fat transfer is a technique used to harvest the fat from different areas of the body using liposuction. This includes the abdomen, the flanks, the sides or any area that you have excess fat. This fat is collected in a sterile canister. When the fat is removed with liposuction, essentially the fat cells are harvested in such a way that they do not have their own blood supply. When they are part of the body, the blood supply will easily nourish the fat. That is why when we gain weight fat stays there forever. It becomes part of the body. When we harvest the fat, it essentially destroys the blood supply to the fat. When fat is transferred to any specific area, it behaves as a graft, and a graft is any given tissue that is transferred to a different anatomical place without its own blood supply. This is important, because when you transfer any tissue to any given area, first the recipient bed needs to have a significant blood supply. Number two it takes a while for the fat or any graft to be taken by the body. The fat essentially survives by the surrounding blood fluid that is bathing the graft at that point. This is the reason that any stress to the fat early after it is grafted can cause significant damage to the fat. This includes infection, smoking, and pressure. Because the fat does not have its own blood supply, when you apply pressure, it essentially diminishes the surrounding tissues perfusion to that fat in the recipient bed. This means that the fat is not going to take successfully if any given stress is provided. In about two weeks, the fat transfer becomes islands of fat cells which then are taken by the body. This is the reason that after fat transfer, if you gain weight, the area that you transfer the fat is going to get bigger. If you lose weight, the area that was transferred is going to get smaller. So first the fat graft survives by essentially diffusion. The process where nutrients just enter the cells by its surrounding recipient bed, subsequently blood supply, will start growing into the fat which allows the fat cells to have a direct bridge of nutrients to be delivered. Fat grafting is still an area of constant change and we keep coming up with better equipment and better technique to make the fat transfer successful. Understanding how fat transfer work goes along with your recovery, and why it is important not to sit for the first two weeks.