Beyond Sarcopenia: A Systematic Review and Meta-Analysis on Muscle Outcomes After Bariatric Surgery.

BACKGROUND

Metabolic and bariatric surgery (MBS) produces substantial and sustained weight loss, but concerns remain about skeletal muscle loss and sarcopenia.

METHODS

We conducted a systematic review of longitudinal and cross-sectional studies evaluating changes in muscle quantity, strength, and physical performance following MBS without interventions to preserve muscle. Searches were performed in PubMed, EMBASE, CINAHL, Web of Science, and Cochrane Central, and the review was registered with PROSPERO (CRD42022354153). Study quality was assessed using the Evidence Project Risk of Bias Tool. Meta-analyses were performed using standardized mean differences (SMDs) with random-effects models.

RESULTS

Sixty-six reports from 64 studies were included, covering diverse surgical procedures and populations. Absolute muscle quantity declined at all timepoints, increasing over time (1-year SMD -0.80 [95% CI -0.97 to -0.63]), while relative muscle mass generally increased. Greater total weight loss predicted larger absolute muscle losses. Cross-sectional comparisons with non-surgical controls showed no consistent differences, although heterogeneity was high. Lower-body functional strength (e.g., chair stand) typically improved, while absolute arm and leg strength modestly declined or remained stable. Physical performance outcomes generally improved, suggesting preserved or enhanced functional capacity.

CONCLUSION

Muscle loss after MBS appears largely adaptive, proportional to weight loss, and does not consistently impair functional capacity. Absolute and relative changes should be interpreted in the context of overall weight reduction. Adoption of standardized outcome measures and obesity-specific normative data for muscle quantity and function is needed to improve the early detection of sarcopenia and to distinguish adaptive muscle loss from clinically meaningful impairments after MBS.