A prospective study investigated the effects of weight loss induced by lifestyle change on histological features of NASH. Liver biopsy samples were taken from participants with NASH at the start and the end of the study, 52 weeks later. All patients who had lost ≥5% of their initial weight showed substantial improvements at week 52. Extent of weight loss positively correlated with histological improvements. The largest reduction in NAFLD activity score, NASH resolution (90%) and fibrosis regression (45%) occurred in patients who lost ≥10% of their initial weight.