Background & aims: Weight loss in overweight or obese individuals results in marked improvement or resolution of hypertension, diabetes mellitus, and hyperlipidemia. However, the overall effect of weight loss on nonalcoholic fatty liver disease (NAFLD) remains unclear. This systematic review and meta-analysis is an effort to explore the effect of weight loss after bariatric surgical procedures on NAFLD.

Methods: We performed an electronic literature search of published articles on bariatric surgery and liver histology since inception to September of 2007. Primary outcome measures were improvement and/or resolution in the 3 components of NAFLD (steatosis, steatohepatitis, and fibrosis) after bariatric surgery-induced weight loss. A pooled proportion of patients with improvement or resolution was calculated for steatosis, steatohepatitis, and fibrosis using a random effects model. Heterogeneity among the studies was assessed using the I(2) (inconsistency) statistic and subgroup analyses.

Results: A total of 15 studies (766 paired liver biopsies) were selected for final data extraction. The percentage reduction in mean body mass index after bariatric surgeries ranged from 19.11 to 41.76. The pooled proportion of patients with improvement or resolution in steatosis was 91.6% (95% confidence interval [CI], 82.4%-97.6%), in steatohepatitis was 81.3% (95% CI, 61.9%-94.9%), in fibrosis was 65.5% (95% CI, 38.2%-88.1%), and for complete resolution of nonalcoholic steatohepatitis was 69.5 (95% CI, 42.4%-90.8%).

Conclusions: Steatosis, steatohepatitis, and fibrosis appear to improve or completely resolve in the majority of patients after bariatric surgery-induced weight loss.