Evolving indications for metabolic and bariatric surgery

This chapter addresses patient selection for metabolic and bariatric surgery (MBS) in the modern obesity care landscape, where anti-obesity medications (AOMs) such as semaglutide and tirzepatide have changed the clinical decision-making framework. We organize the evidence around four questions a clinician actually asks: who qualifies under current guidelines, who benefits most and from which procedure, who is poorly served by surgery, and when pharmacotherapy is the better answer. We review the evolution of indications from the 1991 NIH Consensus Conference through the 2022 ASMBS/IFSO joint guidelines, with attention to the randomized evidence supporting expanded indications at BMI 30-34.9 kg/m² with type 2 diabetes. We then examine outcomes by patient phenotype, including type 2 diabetes, dyslipidemia, hypertension, metabolic dysfunction-associated steatohepatitis, obstructive sleep apnea, heart failure, transplant candidacy, polycystic ovary syndrome, pregnancy planning, and elevated cancer risk. We identify populations for whom surgery carries an unfavorable risk-benefit profile, including patients with advanced perioperative risk, decompensated cirrhosis, untreated psychiatric illness, active substance use, or inability to maintain long-term nutritional follow-up. Finally, we provide a comparative analysis of MBS and modern AOMs across cardiometabolic outcomes, with attention to the methodological limitations of current cohort comparisons and the role of combination and sequential strategies. The chapter concludes that the two modalities are converging on a complementary framework in which patient phenotype, not BMI alone, determines the right intervention.