Obesity is a frequent disease with an increased prevalence, estimated to 12.4% in France (OBEPI study 2006). Non alcoholic fatty liver disease (NAFLD) and non alcoholic steatohepatitis (NASH) both complicate morbid obesity and could be responsible for the development of liver fibrosis and consequently of liver cirrhosis. Bariatric surgery has been widely used in obese patients to reduce their weight but also to decrease morbidity conditions related to obesity. It could be involved in an improvement in liver lesions observed in obese patients. To evaluate the severity of liver lesions, the gold standard is pathological examination of the liver using percutaneous or surgical biopsies, with a scoring called Fibrosis score stage. Alternative less invasive techniques have been developed to evaluate liver lesions. These tests are commonly used in clinical hepatology and consisted of serum levels determination of fibrosis markers (Fibrotest, Transthyretin).

The aim of this study is to evaluate the evolution of fibrosis scores during weight loss in a population of patients operated on for morbid obesity ( BMI > 40kg/m2 or BMI> 35kg/m2 with comorbidity). The primary end point is to evaluate the concordance between Fibrotest and transthyretin serum levels. The number of patients has been calculated on the basis of a concordance ( Kendall test) superior to 70% in patients with grade F1 fibrosis that represents about 40% of morbid obese patients. A total of 255 patients has to be enrolled in this study. According to the number of patients operated on in the 3 centres (>150/year), the time for recruitment is 12 months. Secondary end points will evaluate in these patients the excess weight loss, the improvement in fibrosis liver tests and the correlation with improvement in other obesity- related conditions, according to surgical procedures.

Inclusion Criteria:

• patients operated on for morbid obesity (BMI >40kg/m2 or >35kg/m2 associated with comorbidity)

Exclusion Criteria:

• contraindications to morbid obesity surgery