Could I Take Fat from a Family Member and Use It?

Many patients with a good physique and little to no body fat inquire if they can use a family member's body fat to inject, and unfortunately the answer is no. The body will reject the fat because it recognizes it as a foreign body and the immune system will attack it. There is also a risk of developing an infection as well. Most doctors are able to locate some fat on the patient, and if not then they can simply gain some weight for the procedure. Be sure to consult with a board certified plastic surgeon when discussing your procedure.

Unfortunately, you cannot use fat from a friend or family member, unless he/she is your identical twin (not fraternal). 

Unless you borrowed fat from a genetically identical twin, the fat would be rejected and would completely disappear in short order.