ORIGINAL CONTRIBUTIONS The Effects of Sleeve Gastrectomy and Gastric Bypass on Branched-Chain Amino Acid Metabolism 1 Year After Bariatric Surgery Hong Chang Tan 1 & Chin Meng Khoo 2,3 & Matthew Zhen-Wei Tan 1 & Jean-Paul Kovalik 3 & Alvin Choong Meng Ng 4 & Alvin Kim Hock Eng 5 & Oi Fah Lai 6 & Jian Hong Ching 3 & Kwang Wei Tham 1 & Shanker Pasupathy 7 # Springer Science+Business Media New York 2015 Abstract Background Weight loss, early after Roux-en-Y gastric by- pass (GB) surgery, is associated with reduced concentrations of plasma branched-chain amino acids (BCAAs) and im- proved insulin sensitivity. Herein, we evaluated whether changes in BCAAs and insulin sensitivity persist with weight stabilization (1 year) after GB or sleeve gastrectomy (SG). Methods We prospectively examined 22 severely obese pa- tients (mean age 40.6± 2.1 years, BMI 38.8± 1.3 kg/m 2 , and 59.1 % female) who underwent SG (n = 12) or GB (n = 10) for morbid obesity. Body fat composition was measured with dual X-Ray absorptiometry and abdominal fat volume with com- puted tomography. BCAAs and acylcarnitines were profiled using liquid chromatography with tandem mass spectrometry. Insulin resistance was calculated using the homeostasis model assessment for insulin resistance (HOMA-IR) formula. Results At 1-year follow-up, the decrease in BMI, body weight, total fat mass (TFM), fat free mass, and visceral adi- pose tissue (VAT) was similar between SG and GB. HOMA- IR was associated with BCAA concentrations, and both were decreased equally in both surgical groups. In multivariate analysis with BCAAs, TFM, and VAT as independent factors, only VAT remained significantly associated with insulin resistance. Conclusions The metabolic benefits from bariatric surgery, including the changes in BCAA profile, are comparable be- tween SG and GB. The reduction in BCAAs and improve- ment in the AC profiles after bariatric surgery persists up to 12 months after surgery and may not be surgical related but is influenced primarily by the amount of weight loss, in partic- ular the reduction in visceral adiposity. Keywords Sleeve gastrectomy . Gastric bypass . Branched-chain amino acids . Visceral adipose tissue . Insulin resistance Introduction Branched-chain amino acids (BCAAs) have been shown to directly modulate insulin resistance [1, 2], and multiple stud- ies have demonstrated a significant reduction in the blood concentration of BCAAs that accompanies the dramatic im- provement in body weight and metabolic parameters after bariatric surgery [3–6]. In this regard, the reduction in BCAAs after bariatric surgery has been proposed as one of the possible mechanisms that contribute toward post-surgical * Hong Chang Tan tan.hong.chang@sgh.com.sg 1 Department of Endocrinology, Singapore General Hospital, The Academia Level 3, 20 College Road, Singapore 169856, Singapore 2 Department of Medicine, National University of Singapore, Singapore, Singapore 3 Cardiovascular Metabolic Program, DUKE-NUS Graduate Medical School, Singapore, Singapore 4 The Endocrine Clinic, Mount Elizabeth Novena Specialist Centre, Singapore, Singapore 5 Department of Upper GI and Bariatric Surgery, Singapore General Hospital, Singapore, Singapore 6 Department of Clinical Research, Singapore General Hospital, Singapore, Singapore 7 Advanced Laparoscopic Surgery, Gleneagles Hospital, Singapore, Singapore OBES SURG DOI 10.1007/s11695-015-2023-x