BBL for skinny petite Asian girl: Can I get a BBL without gaining weight? (Photos)

Patients interested in BBL often ask questions of the necessary volume for transfer. Ultimately, the answer is two pronged and based upon both patient expectations and the nature of fat graft themselves.
BBL and fat transfer is ultimately dependent upon the long term viability of the fat grafted. That being said the resorption rates of fat transferred can be significant. Clinically this translates to a progressive loss of grafted volume in the months following the procedure.
I tell patients that they can expect resorption or graft loss on the order of 50% (at most; prepare for the worst and hope for significantly better). Additionally some harvest volume is lost in processing the fat graft prior to transfer. Thus I generally recommend that patients seeking even the most minimal volume increase have adequate reserves for grafting of 500 cc per cheek (at minimum).  This means that harvest will usually exceed 1 liter (assuming for processing loss).
However, it important to remember that these are recommendations and can be amended based upon a patient's particular expectations. Some patients only want a subtle change and may be willing to accept a less significant result. But the rule still applies you have to have the fat to transfer the fat.
With regards to your specific question, you appear to have moderate reserves available for transfer. The best candidates are healthy and have reached a healthy stable weight (preferably with a BMI < 30). I don't typically encourage weight gain (unless you plan to maintain that weight post op) as the transferred volume can be lost.
Ultimately, "enough" is relative to expectations. Those seeking dramatic changes need to have the available donor fat. However, your donor fat do not determine your candidacy for surgery. Your candidacy is defined by your expectations. As long as your goals are in line with what can be realistically achieved, then you can proceed.
As always, discuss your concerns with a board certified plastic surgeon (ABPS).

You have very little excess fat for a BBL. If you gained weight before surgery, as was recommended to you, the fat would accumulate in areas that can then be suctioned out during your BBL. The advantage of this is the fat from those areas would be transferred to your butt and hips and if you did gain weight after surgery instead of accumulating all the fat in those same areas your buttocks tends to get bigger. A number of patients would find this as a positive ie they gain weight and most of the fat is deposited into their buttocks. Please note that some patients may find this as a negative. At the recent aesthetics society meeting that was held in New York this year, the society strongly recommended that if you are going to perform a BBL, you should inject fat only in the fatty tissue above the muscle. Many surgeons inject fat into the muscle and the society feels that it is much safer to inject fat above the muscle. Over a year ago I started using a new high tech device, called the Vibrastat. It allows for performing BBLs in the soft tissue layer above the muscle. I hope you find this information useful. Please watch the enclosed video.