Non-alcoholic fatty liver disease (NAFLD) is caused by the accumulation of lipids inside hepatocytes; it can be simple or it can be inflammatory. Its prevalence has been increasing in recent years and is predicted to become the most common indication for liver transplantation by 2030. NAFLD is a multifactorial disease, although patients with metabolic disorders are at higher risk of developing it, and in more severe forms. Liver fat originates from the increase of free fatty acids (FFA), from de novo lipogenesis and from diet. This review compile evidence of the involvement of unregulated enzymes in the synthesis of fatty acids (FA), the alteration of FA transport proteins, and the presence of diverse polymorphisms, which may be associated with an increased risk of NAFLD. © Acta Gastro-Enterologica Belgica.