ABSTRACT

I. Introduction .......................................................................................................................... 562 II. The Nature and Function of Dietary Lipid .......................................................................... 562 III. Digestion and Absorption of Lipid ...................................................................................... 562 A. Digestion in the Intestine ............................................................................................... 562 B. Absorption of the Products of Digestion ....................................................................... 563 C. Metabolism of Absorbed Lipid in the Enterocyte ......................................................... 563 D. Assembly of Triacylglycerol-Rich Lipoproteins ........................................................... 564 E. Absorption of Short-Chain Fatty Acids ......................................................................... 565 IV. Transport of Lipid on Lipoproteins ..................................................................................... 565 A. Structure of Lipoproteins ............................................................................................... 565 B. Synthesis of Lipoproteins .............................................................................................. 567 C. Synthesis of VLDL ........................................................................................................ 567 D. Synthesis of HDL .......................................................................................................... 567 E. Lipoprotein Metabolism ................................................................................................ 568 F. Chylomicron Metabolism .............................................................................................. 568 G. VLDL Metabolism ........................................................................................................ 570 H. Receptor-Mediated Uptake of Lipoproteins .................................................................. 571 a. Chylomicron Remnant Receptors (E) ....................................................................... 571 b. LDL Receptors, B100/E ............................................................................................. 571 I. Receptor-Independent Uptake of LDL .......................................................................... 572 a. β-VLDL Receptor ..................................................................................................... 572 b. “Scavenger” or Acetyl LDL Receptor ...................................................................... 572 J. HDL Metabolism ........................................................................................................... 573 K. Reverse Cholesterol Transport ...................................................................................... 573 L. Lipid Transfer Protein ................................................................................................... 574 M. Utilization of Cholesterol .............................................................................................. 575 N. Desaturation Reactions .................................................................................................. 575 O. Dietary Control .............................................................................................................. 576 P. Hormonal Control ......................................................................................................... 577 V. Effect of Dietary Lipid on Lipoprotein Cholesterol ............................................................ 577 A. Dietary Cholesterol ........................................................................................................ 577 B. Human Studies .............................................................................................................. 577 C. Animal Studies .............................................................................................................. 578 D. Dietary Fatty Acid Composition .................................................................................... 578 E. Triacylglycerol Structure ............................................................................................... 579 F. Level of Dietary Lipid ................................................................................................... 579 VI. Possible Mechanisms of the Hypocholesterolemic Effects of Dietary

Polyunsaturated Fatty Acid .................................................................................................. 579 A. Effects on Cholesterol Metabolism ............................................................................... 579 a. Reduced Absorption of Cholesterol .......................................................................... 579 b. Redistribution of Cholesterol to Tissues ................................................................... 579

In recent years, there has been considerable interest in determining both the amount and type of fat in the diet that commensurate with good health. This has led both to of@ cial reports such as the Committee on Medical Aspects (COMA) of food policy reports (Department of Health and Social Security, 1984; Department of Health, 1991) and to books offering nutritional advice to the general public (e.g., Anderson, 1986; Le Fanu, 1987). This chapter considers the absorption, transport, and desaturation of dietary lipid and some of the possible effects on human health.