Lipids have physical, chemical, and physiological properties that make them important factors in human nutrition. They form a group of compounds of varied chemical nature that have the common property of being soluble in organic solvents but insoluble in water. This basic property affects their digestion, absorption, and transport in the blood and metabolism at cellular level. Firstly, fatty-acid chain length and number of double bonds influence fat absorption. Thus, medium-chain fatty acids (MCFA) are better absorbed than long-chain fatty acids. Secondly, the positional distribution of fatty acids (FA) in dietary triglycerides (TG) determine whether FA are absorbed as 2-monoglycerides (2-MG) or free fatty acids (FFA), and hence, influences, the composition of chylomicroms (CM) because triglycerides (TG) are resyntethysed in the intestinal mucosa using 2-MG from dietary lipids. Generally, the absorption of FA in the sn-2 position of TG is favored, whereas no specificity has been found for the fatty acids in the sn-1 and sn-3 positions. Finally, some FA of nutritional interest, namely, long-chain polyunsaturated fatty acids (LCP), are present in dietary lipid sources as both TG or phospholipids (PL). Fatty acids esterified as PL or TG may show different availability. In fact, some authors have suggested a better absorption of LCP-PL. Moreover, dietary LCP in form of TG or PL differently affects the composition of HDL and LDL PL. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.