Nonalcoholic fatty liver disease is currently the most common cause of chronic liver disease. In general terms, its overall prevalence varies between 20% and 50% in Western countries and it is the leading cause of hepatocellular carcinoma and will be the most important etiology for liver transplantation referral by 2020. It can be divided into the histological categories of nonalcoholic fatty liver, which includes patients with isolated hepatic steatosis and patients with steatosis and mild nonspecific inflammation, as well as nonalcoholic steatohepatitis, which is distinguished from the former by the additional presence of features of hepatocellular injury with or without fibrosis. Nonalcoholic steatohepatitis is considered to be the progressive subtype of NAFLD; however, data suggest that hepatic steatosis with inflammation has a distinct and more progressive natural history than isolated hepatic steatosis. Fatty liver is a condition very frequently linked to obesity since it is found in 10%-15% of normal weight individuals and in 70% of obese subjects. Therefore NAFLD has been recognized as a hepatic manifestation of metabolic syndrome linked to insulin resistance.
Because it shares several pathophysiological pathways and epiphenomena with obesity itself and the rest of “classical” related comorbidities, bariatric surgery has been recognized as an useful tool for the treatment of fatty liver disease, specially if obesity is present. Bariatric surgery modifies some of the pathophysiological phenomena observed in NASH and could be considered a safe treatment and the most effective treatment for NAFLD/NASH to date that offers excellent results with benefits beyond weight loss. However, there are several concerns about the possibility of treating patients with a severe liver condition using bariatric surgery due to the side-effects of malabsorptive techniques and because liver-failure has also been typically considered a risk factor for postoperative complications.
The vast majority of the positive effects of bariatric surgery in terms of physiological changes could be beneficial also in NAFLD/NASH patients since these procedures improve two key factors in the fatty liver disease pathophysiological pathways: inflammation and insulin-resistance. After bariatric surgery, several effects that can alter NAFLD/NASH pathogenesis occur including better insulin secretion and sensitivity, diminished insulin resistance and glucose output, an overall improvement in the obesity-related proinflammatory status, enhanced lipid exportation and beta-oxidation, diminished or even arrested fibrosis and changes in the gut microbiome.
To date, the beneficial effects of bariatric surgery on fatty liver disease have been assessed mainly by observational studies in which clear laboratory data improvement has been observed as well as a 75% decrease in the steatosis rate, a downstaging of the NAFLD score from 1.9 to 1 and a decreased fibrosis rate by about 65-70% with a 65% NASH resolution rate. Also, it is thought that BS can stop the development of NASH in up to 50% of patients if it is performed during the first 5 years.
Many Scientific Societies are aware of the beneficial effects of BD on fatty liver disease and are publishing some recommendations in order to consider it a valid option for treating NAFLD or NASH. However, many of them afirm that nowadays maybe it is premature to consider foregut surgery as an option to specifically treat fatty liver disease. Nevertheless, Surgical Societies, such as IFSO consider that end-stage liver failure and/or cirrhosis remain a major contraindication for bariatric surgery but indicate that weight-loss surgery is able to induce not only an improvement but also resolution of NAFLD.
In conclusion it can be said that bariatric surgery can improve both the clinical and histological parameters of NASH via other mechanisms other than weight. However, all the available information is based only on observational studies and, therefore, there is a clear need for large scale clinical studies in order to evaluate the role of bariatric surgery as a viable option for the treatment of NAFLD in the obese population and, maybe, consider it as an indication as happened with type 2 diabetes and metabolic surgery.
Nonalcoholic fatty liver disease is currently the most common cause of chronic liver disease. In general terms, its overall prevalence varies between 20% and 50% in Western countries and it has been recognized as a hepatic manifestation of metabolic syndrome linked to insulin resistance. In this lecture, Dr. Balibrea discusses several aspects of the effects of bariatric surgery on nonalcoholic fatty liver disease