Should I lose or gain weight for BBL if I want curvy hips & bubble butt? (Photo)

A good candidate has enough fat available for transfer in the procedure. The amount of fat that can be transferred in a BBL depends on how much fat the patient has to harvest and the amount of space there is to move the fat into. It is recommended for the patient to have a BMI of 30 or less. If you are too thin, a Brazilian Butt Lift may not be possible.

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.
The question is ultimately a function of your goals. Enough? is a relative question. This is best determined via in-person consultation. Optimally, you should be at a healthy stable weight (preferably with a BMI < 30) with adequate donor sites for harvest. I do not recommend weight gain unless you intend to maintain post op.
With regards to your specific question, I would discourage weight gain for the purposes of harvest alone unless you plan to maintain at a heavier weight. It is important to remember that anatomy plays a role in defining your waistline. Some may be naturally "curvier" (smaller waist to hip ratio) than others. If you have (at some point) had a much narrower waist, this may be reached via liposuction and the hips and buttocks can be subsequently accentuated via fat transfer.The key is reach a healthy stable weight prior to surgery (preferably with a BMI < 30).
As always, discuss your concerns with a board certified plastic surgeon (ABPS).

Dear bay_area_beauty,
you should know that for this type of surgery, it is very important to have a stable weight in order to be a good candidate. If you loose or gain weight prior to surgery, it can have a negative effect on your surgery results. 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