Anatomy-Aware Effects of Biliopancreatic-Limb Length in Roux-en-Y Gastric Bypass: A Systematic Review and Meta-analysis.

Trials labelled "long" biliopancreatic limb (BPL) test different Roux-en-Y gastric bypass configurations. We separated fixed-alimentary-limb BPL extension, reciprocal limb reallocation, distalization, and compound changes. The registered primary outcome was 12-month HbA1c in baseline type 2 diabetes. Eighty reports represented 39 studies (14 randomized trials, 25 cohorts). Primary HbA1c differences were - 0.18% points (95% CI - 0.59 to + 0.23) for fixed-limb extension and - 0.33 (- 0.60 to - 0.06) for reallocation; these classes were not pooled. Two fixed-limb trials (146 participants) yielded a secondary 12-month percentage total weight-loss difference of + 0.36 points (- 0.60 to + 1.32). Glycemic evidence remains sparse and configuration-specific. Fixed-limb evidence is inconsistent with a 5-point weight-loss gain but does not exclude smaller effects or identify the isolated BPL effect. KEY POINTS: • Only three of 14 RCTs tested fixed-AL BPL extension; one measured the CC. • Primary 12-month HbA1c could not be pooled within an anatomical class. • Fixed-total reallocation suggested a modest HbA1c package effect. • Allocation shifts and distalization cannot identify an isolated BPL effect.