How Do I Gain Weigh in my Hips and Butt?

At that height and weight, don't let anyone talk you into fat grafting BUT there is definite hope...

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/Hip Implants (semi-solid silicone rubber implants that cannot rupture &/or leak). Both are very good 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 gain weight for the procedure, the fat that you lose first when you go back down to your baseline weight after surgery is in fact that fat that you originally gained and transferred into your buttocks...so don't fall victim to this recommendation.  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 can also 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 subsequent 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 single 2 ½ inch long incision over the tailbone (concealed within the crevice between the buttock cheeks) and the hip implants through a ~ 1 inch incision just below the beltline above the hip region. 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… 

     If you really want to gain weight, you can gain 20 lbs or so and see how the fat distributes.  If you are happy with the distribution, great.  If you want some areas liposuctioned and other areas built up with fat, this can be done as well.  Find a plastic surgeon with ELITE credentials 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, MD Los Angeles, CA

What you are asking about is how to change your shape.  The answer is by undergoing body contouring surgery.  You can't "force" your body into a shape that is not within its genetic makeup.  If weight gain results in a larger abdomen and waist with continued flat buttocks and narrow hips, the ONLY way to alter your shape is by having liposuction of the abdomen and waist and fat grafting of the hips and buttocks.  Good luck!