Association of Weight Loss Composition Following Metabolic-Bariatric Surgery With Incident Major Adverse Cardiovascular Events and All-Cause Mortality.

Severe obesity is associated with an increased cardiovascular risk. Metabolic-bariatric surgery (MBS) can reduce the risk of cardiovascular events and mortality, potentially depending on weight loss composition. This study assessed the association between post-MBS weight loss composition and major adverse cardiovascular events (MACE) and all-cause mortality. This retrospective, single-center study included patients who underwent MBS between 2012 and 2020. Twelve-month total weight loss (TWL), fat mass loss (FML), fat-free mass loss (FFML), and proportion of FFML within weight loss (FFML/WL) were assessed. The primary endpoint was a composite of MACE and all-cause mortality. The event rate was compared across weight composition tertiles, while adjusting for cardiometabolic medication, age, sex, preoperative weight and surgery type. In total, 5889 patients (21% men; 44.3 ± 11.1 years) were included. During a follow-up of 4.9 ± 2.2 years, a total of 106 patients (1.8%) reached the primary endpoint. TWL, FFML, FML and FFML/WL were not associated with the composite endpoint after adjustment for confounders. Nevertheless, stratified analysis revealed that older patients (≥ 45 years) with a high TWL (HR = 1.68 [95% CI, 1.03-2.75]) and high FFML/WL (HR = 1.78 [95% CI, 1.12-2.85]) had a higher risk of MACE and all-cause mortality. Weight loss composition was not related to MACE and mortality in the total population, but higher TWL and FFML/WL ≥ 30% at 12 months post-MBS were associated with a worse prognosis among patients aged ≥ 45 years. The harm associated with excessive TWL and FFML post-MBS, along with potential countermeasures, should be further investigated to optimise clinical outcomes.