AMP-activated protein kinase (AMPK) is a master regulator of multiple cellular metabolic pathways, including lipid metabolism. Some of the well-known substrates of AMPK are acetyl-CoA carboxylase (ACC) and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, regulatory enzymes of fatty acid and cholesterol synthesis, respectively. The discovery that both of them are inactivated by AMPK suggested the therapeutic potential of AMPK activation in the treatment of metabolic diseases associated with lipid disorders, such as nonalcoholic fatty liver disease (NAFLD). Here we describe a method to measure lipid synthesis flux in intact cells from the saponifiable (including fatty acids) and non-saponifiable (including sterols) fractions of lipid extracts.