Fasting state lipid metabolism

Details of plasma lipoproteins and their metabolism are given in Section 5.5. Most of the cholesterol in the blood is carried as part of low density lipoprotein (LDL) or high density lipoprotein (HDL), whereas most triglyceride, in the fasting state, is carried by very low density lipoprotein (VLDL). The relative concentrations of these lipoproteins constitute the lipid profile and determine CVD risk. Diabetics are more likely to show an unhealthy profile with elevated concentrations of LDL and triglyceride but reduced HDL concentration. This pattern can be partly explained by enhanced fatty acid liberation from adipocytes as a consequence of insulin resistance in that tissue and due to reduced removal from the circulation of triglycerides, which is also insulin dependent. 

The liver also plays a central role in the regulation of lipid metabolism. When fuels are abundant, fatty acids derived from the diet or synthesized by the liver are esterified and secreted into the blood in the form of very low density lipoprotein (see Figure 30.15). However, in the fasting state, the liver converts fatty acids into ketone bodies. How is the fate of liver fatty acids determined The selection is made according to whether the fatty acids enter the mitochondrial... 

In the fasted state, the fatty acid composition of lipoprotein lipids reflects their biosynthetic origins and metabolic transformations in circulation (Table 2) [6]. 

The purpose of this chapter is to summarize and integrate the major pathways for the utilization of carbohydrates and fats as fuels. We will concentrate on reviewing the regulatory mechanisms that determine the flux of metabolites in the fed and fasting states, integrating the pathways that were described separately under carbohydrate and lipid metabolism. The next section of the book covers the mechanisms by which the pathways of nitrogen metabolism are coordinated with fat and carbohydrate metabolism. 

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