The doctors ask the patients to lose weight for 2 reasons: 1st SAFETY: high BMI increases the risk of complications, like seromas and DVT (blood clots that can cause pulmonary embolism) 2nd RESULTS: You may not get the best results if you do plastic sugery with obesity. Plastic surgery will improve your shape but it is not a treatment to lose weight. If you do the surgery and lose 25 to 30lb after there will be loose skin on your belly or sagging of the breasts.