Non-Alcoholic Fatty Liver Disease (NAFLD) is one of the most prevalent chronic liver diseases in Brazil. It has a significantly increasing incidence today and is considered an important global health problem. It affects approximately 20 to 30% of the adult population and increases according to the severity of the risk factors. The diagnosis of this disease usually occurs in 10 to 20% of the non-obese individuals, 50% in the overweight and 80 to 90% in the obese, being twice as present in individuals with Metabolic Syndrome. Pharmacological treatment options for NAFLD are still limited and Silybum marianum, one of the most sought-after herbal remedies in patients with liver disease, is commonly used by patients because of the claim of the hepatoprotective effect of silymarin. Studies have demonstrated the therapeutic potential of silymarin in patients with NAFLD, but clinical trials with more judicious methodological designs is still needed to prove these effects. Thus, this project aims to evaluate the efficacy of silymarin in adult patients with NAFLD seen at the Clinic of Nutrition and Hepatology of Edgard Santos Hospital. A randomized, double-blind, controlled clinical trial lasting 12 weeks will be performed.