How long does Fat Injection typically last? Would I loose the shape in case I loose weight?

Fat transfer has a consistent survival rate of approximately 30-40% based on the harvest and separation technique.  There is always some level of swelling after any surgery so there is some overcompensation and techniques that is typically done to take that information into account to get the desired shape.  My recommendation is to find a surgeon who does over 3-4 surgeries like this per month and get his or her opinion on what they feel their technique is achieving.  Best Wishes!!

Allow me to share with you some information that you may not hear elsewhere. There are
only two proven safe and relatively effective methods for Buttock Augmentation
and Hip Augmentation: 1) Autologous Fat Transfer (using your own fat,
transferring from one area of the body to the other) and 2) Buttock Implants (semi-solid silicone rubber implants that cannot rupture &/or
leak). Both are acceptable options so what it comes down to, like any surgery,
is proper patient selection. Indeed because at least 50+ % of the fat
transferred will melt away within a year, most patients are not good candidates
because they lack an adequate amount of fat to harvest. Another tip is that if
you purposely gain weight (i.e. fat) for the procedure, the fat you lose first
as you get back to your baseline weight is that very same fat that was
transferred into your buttock...so don't fall victim to this
recommendation.  I unfortunately see at least about one patient per week who had this happen to them and now they are seeking implants.  Although using your own fat is relatively safe, the one
serious complication that can rarely (< 1%) happen is "fat
embolism" in which some of the fat gets into the blood stream and travels
up into the lungs, heart, and/or brain causing serious problems. This
complication is more likely to happen with the larger amount of fat being
transferred. This is
even more likely to happen when using fillers like PMMA and hyaluronic acids.
Also fillers, when injected in large quantities, have a relatively high
tendency to migrate away from the original area they were placed and tend to
stimulate a lot of inflammation and a subsequent disastrous amount of scar
tissue/hardening.

Thus
buttock/hip implants become a very good, safe, and long term reliable option
for most patients seeking buttock augmentation (at least in my practice). I
prefer to insert the buttock implants through a 2 inch long incision
over the tailbone (concealed within the crevice between the buttock cheeks). The buttock implant should always be placed under or within the
gluteus maximus muscle. In this position, the implant is less palpable, less
visible, and does not sag or shift/migrate over time unlike implants placed on
top of the muscle. Therefore it is extremely important to seek consultation
with a board certified plastic surgeon who specializes in this procedure. And
in this case too, at least in my surgical practice, the infection rate is
minimized to <5%. Glad to help.

The fat that is grafted will become part of you.  If you lose weight it will shrink, and if you gain weight it will get larger.Try to research this to find the surgeon who consistently produces the
results you would expect. Look at reviews on this site and see who gets the surgery right every time. Find
a board certified plastic surgeon who performs hundreds of Brazilian
buttlifts each year. Then look at the plastic surgeon's
website before and after photo galleries to get a sense of who can
deliver the results. Kenneth Hughes, MDLos Angeles, CA