Is there breast sensitivity loss after a fat transfer?

Although there are risks of changes in nipple sensitivity with all breast surgeries generally speaking the incidence of this is much less common than with traditional breast augmentation with implant.  Patients with smaller volume of breast tissue are relatively higher risk in such procedures.  Talk to you board certified plastic surgeon about this concern to get a better idea of your individual risk factors.  

Many thanks of your question.
As you state, breast sensitivity can be altered after breast implants, however this usually resolves with time.
In my experience of fat grafting breasts, I have never seen a case where breast sensitivity is altered from the pre-injection state, but that does not mean that it cannot occur.
Whilst the fat grafting may initially result in some swelling and/or bruising to the breast, it does not cut into or under the breast and therefore carries minimal risk of damage to the sensory nerves of the breast.
I hope this goes some way to answering your question. If you are having fat transfer to your breasts then I would always advise seeking the expert advice and skills of a Board certified Plastic Surgeon with experience in this procedure in order to maximise the fat survival and thus, ultimate outcome of your surgery.
Good luck and best wishes.
Marcus