Why does breast fat transfer have so little retention compared to a BBL?

In general, 200 cc per breast is typically the upper limit of fat injection recommended by most plastic surgeons.  It is not that more cannot be injected; but on average, this has been determined to be the most that can be expected to live during one transfer.  Multiple transfers would be required for additional cc's.  In general, the abdomen and thighs are preferred donor sites.
Some of the retention rate will depend upon the amount of fat transferred, as smaller volumes will likely have a higher survival.  Occasionally, a patient can resorb a great deal of the fat despite optimal transfer procedures. I typically transfer from 250 cc to 400 cc or so per breast.  Thinner patients are outstanding candidates in my opinion, because the fat transferred is extremely resistant.  
Results are largely dependent upon the skill of the surgeon, his/her ability to remove fat without creating contour deformities, and your expectations. You would need a consultation to determine the available fat stores.
Kenneth Hughes, MD, ABPS Board Certified Plastic Surgeon
Los Angeles, CA

Dear T00313,
in most cases 30-50% of transferred fat is lost. Fat viability depends a lot of surgeon technique. The fat has to be placed back into the breasts as soon as possible so that it has a greater chance of survival. It has to be placed carefully so that not too much fat is placed in only one area. If you are considering a surgery, I would suggest you to consult a board-certified plastic surgeon. Only after a thorough examination you will get more information and recommendations.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

A breast augmentation with implants (teardrop shape or round) may result to rounder, “fake” look, but with the right guidance and after choosing the right shape and size of implants for you this would be only temporary and when they settle the result can look very natural. With regards to fat transfer the retention rate is about 50-70% and it is more related to individual factors (related to the person) rather than the area the fat is transferred to. There are limitations though that can be discussed on a consultation.

The reason why more fat can be injected into the buttocks is that the fat is injected into a bigger structure at many different depths. In the breast most advise that the fat be injected deeper ( under the breast ) and more superficial ( on top of the breast ), but not into the breast itself. Reason - the breast is a gland that later in life has a risk of cancer change. Injecting into the breast itself causes microcalcifications that can confuse the radiologist with mammography. This leaves fewer areas where fat injections are considered safe in the breast area and thus less fat volume injection is possible. If you want anything more than 1 cup size prepare for more than 1 op.

The amount of fat that survives is dependent upon several things, but especially how the fat is transferred and the amount. Some surgeons have good long term success, and some don't. In some areas, like the hands, fat just doesn't stay long because of the location (normally there is not much fat in hands) and movement. If you have little fat or want to be fairly large, breast implants are much more dependable.