Abstract: The present invention is based on the idea of determining certain molecular lipids from a subject's blood sample, for example from serum or plasma sample, and based on the amounts of the determined lipids determining the amount of liver fat and/or diagnosing NAFLD in the subject. More specifically the subjects with elevated liver fat amount and NAFLD are characterized by elevated triglycerides with low carbon number and double bond content in the blood sample. Lysophosphatidylcholines, ether phospholipids, sphingomyelins and PUFA-containing phospholipids are diminished in the blood samples of subjects with an elevated liver fat amount and NAFLD. The method of the present invention can be further used for monitoring the subject's response to the treatment of NAFLD or to the treatment of lowering of the liver fat amount in the subject.