Background & aims: The effects of bariatric surgery in patients with nonalcoholic fatty liver disease (NASH) are not well established. We performed a prospective study to determine the biological and clinical effects of bariatric surgery in patients with NASH.

Methods: From May 1994 through May 2013, one hundred and nine morbidly obese patients with biopsy-proven NASH underwent bariatric surgery at the University Hospital of Lille, France (the Lille Bariatric Cohort). Clinical, biological, and histologic data were collected before and 1 year after surgery.

Results: One year after surgery, NASH had disappeared from 85% of the patients (95% confidence interval [CI]: 75.8%-92.2%). Compared with before surgery, patients had significant reductions in mean ± SD body mass index (BMI, from 49.3 ± 8.2 to 37.4 ± 7) and level of alanine aminotransferase (from 52.1 ± 25.7 IU/L to 25.1 ± 20 IU/L); mean levels of γ-glutamyltransferases were reduced from 51 IU/L before surgery (interquartile range [IQR], 34-87 IU/L) to 23 IU/L afterward (IQR, 14-33 IU/L) and mean insulin resistance index values were reduced from 3.6 ± 0.5 to 2.9 ± 0.5 (P < .01 for each comparison). NASH disappeared from a higher proportion of patients with mild NASH before surgery (94%) than severe NASH (70%) (P < .05) according to Brunt score. In histologic analysis, steatosis was detected in 60% of the tissue before surgery (IQR, 40%-80%) but only 10% 1 year after surgery (IQR, 2.5%-21.3%); the mean nonalcoholic fatty liver disease score was reduced from 5 (IQR, 4-5) to 1 (IQR, 1-2) (each P < .001). Hepatocellular ballooning was reduced in 84.2% of samples (n = 69; 95% CI: 74.4-91.3) and lobular inflammation in 67.1% (n = 55; 95% CI: 55.8-77.1). According to Metavir scores, fibrosis was reduced in 33.8% of patients (95% CI: 23.6%-45.2%). Patients whose NASH persisted 1 year after surgery (n = 12) had lost significantly less weight (change in BMI, 9.1 ± 1.5) than those without NASH (change in BMI, 12.3 ± 0.6) (P = .005). Patients who underwent laparoscopic gastric banding lost less weight (change in BMI, 6.4 ± 0.7) than those who underwent gastric bypass (change in BMI, 14.0 ± 0.5) (P < .0001), and a higher proportion had persistent NASH (30.4% vs 7.6% of those with gastric bypass; P = .015).

Conclusions: Bariatric surgery induced the disappearance of NASH from nearly 85% of patients and reduced the pathologic features of the disease after 1 year of follow-up. It could be a therapeutic option for appropriate morbidly obese patients with NASH who do not respond to lifestyle modifications. More studies are needed to determine the long-term effects of bariatric surgery in morbidly obese patients with NASH.