Background and Aims The increasing prevalence of obesity resulted in more adolescents undergoing metabolic and bariatric surgery (MBS). There are few studies of pre-operative predictors of MBS outcomes in adolescents. The aims of this study were to quantify changes in weight loss and biochemical parameters in adolescents undergoing bariatric surgery and identify preoperative predictors of postoperative weight loss.

Methods This was a prospective, observational cohort study of 73 adolescents (12–19 years) living with obesity who underwent MBS between March 2020 and November 2022 at the SKMC. Absolute and relative changes in anthropometric measures of weight and lipid, HbA1c, and liver function (ALT, AST) parameters were evaluated up to 30 months postoperatively. Differences in anthropometric measures over time were assessed using a mixed residual maximal likelihood model with Tukey’s multiple comparison test, and univariable and multivariable logistic regression were used to identify predictors of a >35.0% reduction in BMI z-score from baseline to 12 months. Predictive accuracy was assessed by ROC-AUC analysis and the optimal cut-point established with Youden’s index.

Results Seventy-three adolescents (65.8% female, mean age (SD) 17.6 (1.83) years) were included in the study. Most patients (87.7%) underwent laparoscopic sleeve gastrectomy. All anthropometric measures of weight (weight, weight z-score, BMI, BMI z-score) significantly decreased over 30 months of follow-up (all p<0.001), with a -4.2%, -14.6%, -23.7%, -35.1%, -39.6%, -40.9%, and -53.8% relative change in BMI z-score at 2 weeks and 3, 6, 12, 18, 24, and 30 months, respectively. The mean (SD) BMI z-score at 30 months was 1.17 (0.8), and all patients had persistent reductions in BMI z-scores compared with baseline. There was a significant increase (p=0.02) in HDL cholesterol and a significant decrease in triglycerides (p=0.0001) and ALT (p=0.0004) after surgery. A higher preoperative BMI was associated with a reduced odds (OR 0.89, 95%CI 0.79-0.97, p=0.03) of a >35% reduction in BMI z-score at 12 months by multivariable logistic regression analysis. A baseline BMI of >52.6 kg/m² had a sensitivity of 100% and specificity of 40.6% for detecting a >35.0% postoperative change in BMI z-score.

Conclusions MBS results in sustained weight loss in adolescents. A high preoperative BMI predicts resistance to optimal weight loss after surgery and argues against delaying surgery once eligibility thresholds are met. These data pave the way for identifying subpopulations of adolescents undergoing MBS who require additional interventions to optimize outcomes.