Should I drink a liquid diet before my BBL?

I do not recommend any specific foods.  I recommend a balanced diet, and I recommend that you maintain a stable weight. Working out four to five times a week is adequate; might spend more time on cardio than lifting weights to drop pounds.  Losing 40 pounds in a month and a half will be a real challenge.  Is this your goal or that of the plastic surgeon who will perform your BBL?  If it is the plastic surgeon's recommendation, I suggest that you meet with him/her again to possibly postpone the surgery. Weight loss plateaus come and go.  You might consult with your primary care doctor for input regarding a weight loss program.  Just remember, the more weight you lose the better your results.  Kenneth Hughes, MD, Board Certified Plastic SurgeonLos Angeles, CA

Two protein shakes and a meal a day is not sustainable long term. Crash diets leave you crashed and burned. Fad diets are fleeting and have temporary results. Those diets have those monikers for a reason!  Once you return to your regular eating habits, the weight will return, if not more. You need a balanced diet to heal, especially postoperatively. 

Dear Ms. Adrimaze,
Thank you for your questions and photos.    Unfortunately without more information ie,  photos, height/weight, past medical history and a examination I can only advise you in general terms, however I hope you will find them helpful.
Loosing or gaining weight will always change your body contour. Loosing 40 lbs in 6 weeks is very optimistic if not impossible. Should you loose weight after the BBL some of the weight may be lost in BBL areas, thus the volume of buttock may be reduced.I suggest you make another appt with your chosen Plastic Surgeon to discuss your long term goals and consider delaying your surgery. It is always best to first obtain your goal body weight.
The amount of fat injected depends on:1) the amount of fat harvested2) the amount of suitable fat that is abel to be purified3) the "stretchability" of your buttock skin
One can try to gain weight prior to the procedure in hope that the areas you gain weight can be liposuctioned.
Caveat: not all weight gain can not be harvested (some may be deposited on your internal organs or areas that can't be liposuctioned.I trust you have chosen a Plastic Surgeon who is  not only Certified by the American Board of Plastic Surgery but in addition ideally a member of the American Society for Aesthetic Plastic Surgery (denoting by membership as having met additional criteria and a focus on Cosmetic Plastic Surgery).
My best wishes, 
Dr. R. A. Hardesty, MD, FACSDiplomate and Certified by the Am. Bd. of Plastic Surgery                            Awardee RealSelf Top 100: 2015 & 2016wwwimagineplasticsurgery.com4646 Brockton AveRiverside, Ca 92506(951) 686-7600