ABSTRACT
Quantitatively, the most important lipid component of the human diet is the triglyceride (TG) fraction, which may amount to 100 g per day. In addition, the diet contains phospholipids, about 5 g per day, and minor contents of cholesterol, cholesteryl esters (CEs), and fat-soluble vitamins. However, the phospholipid and cholesterol present in the digestive tract are not only derived from the diet but also from the bile. The digestion and absorption of TGs are very efcient under normal health circumstances. The composition of the dietary-derived lipids, specically carbon chain length, distribution of fatty acids (FAs) in TG, and degree of saturation of fat affect lipid metabolism. Mediumchain fatty acids (MCFAs) are saturated 6-12 carbon FAs, which occur naturally as medium-chain triglycerides (MCTGs) in milk fat and some vegetable fat sources such as coconut and palm oils. MCFAs represent immediately available sources of energy that can be supplemented to diets to improve energy supply of premature babies, neonates, or patients to treat diseases such as lipid absorption disorders. Structured lipids are lipids that have been modied from their native form either enzymatically or chemically, and these modications may result in changes in FA composition and/or FA position in the TG molecule, which may inuence the fate of the lipid in the body. These diverse structured TGs may be designed according to special requirements such as enhancing lipid absorption or producing low-calorie fats or fat substitutes. Different types of phospholipids have been shown to be of interest in relation to the potential of inhibiting i ntestinal cholesterol absorption, because an increased concentration of cholesterol in the blood (i.e., hypercholesterolemia) is
I. Introduction .......................................................................................................................... 591 II. Digestion and Absorption of Dietary Fat ............................................................................. 592
A. Digestion....................................................................................................................... 593 B. Absorption .................................................................................................................... 594
1. Importance of Micellar Solubilization ................................................................... 594 2. Permeation into Enterocytes and Transport ........................................................... 594
III. Metabolism ........................................................................................................................... 595 A. Resynthesis of TG ........................................................................................................ 595 B. Intestinal Lipoproteins ................................................................................................. 595 C. Assembly of Intestinal Lipoproteins ............................................................................ 596 D. Metabolism of Lipoproteins Secreted from the Intestine ............................................ 596 E. Metabolism of Fatty Acids after Absorption ............................................................... 597 F. Lipogenesis ................................................................................................................... 597
IV. Dietary Fat Modication and Effect on Utilization.............................................................. 599 A. Methods for Investigating Fat Digestibility and Absorption ........................................ 599 B. Importance of Structure of Fatty Acids and TG .......................................................... 599
Summary ........................................................................................................................................ 601 References ...................................................................................................................................... 601
widely recognized as a risk factor for coronary artery disease. The purpose of this chapter is to provide the reader with an insight into digestion, absorption, and metabolism of various lipid components and to explain how dietary fat and modications can inuence lipid digestion, absorption, and metabolism.
