**2.1 Plasma non-esterified FAs**

There are several sources of FAs, including uptake from the blood and DNL, of which uptake from the blood is the major source of FAs for esterification into triacylglycerol (TG) in most conditions (**Figure 1**). The intracellular hydrolysis of TG in the adipose tissue is the largest contribution of FAs uptake from the blood [13], which is under the control of insulin. Insulin inhibits the activity of the two major lipolytic enzymes, including adipose triglyceride lipase (ATGL) and hormone-sensitive lipase. This dynamic process of FA uptake is upregulated during fasting conditions or insulin resistance, while downregulated during post-prandial period [14]. Although plasma concentration of FAs is often elevated in obesity and NAFLD, indicated the effect of insulin resistance, the relationship between insulin resistance and lipolysis is complex. It is identified that FAs release per kilogram fat mass is reduced in obesity, which might be associated with the downregulation of ATGL and hormone-sensitive lipase in adipose tissue [15]. In addition, the elevated postprandial FAs concentration could also be explained that insulin resistance reduces the insulin-mediated inhibition of adipose tissue TG hydrolysis in obesity [16]. Except for the condition of the body itself, the type and amount of dietary fat are also associated with subcutaneous adipose tissue lipolysis. Study found that high-fat diet could reduce the post-prandial suppression of adipose tissue lipolysis compared with moderate-fat diet [17]. Similarly, another study demonstrated that compared with unsaturated fat or free
