Food Lipids: Chemistry, Nutrition, and Biotechnology

19
Dietary Fats, Eicosanoids, and the
Immune System
DAVID M. KLURFELD
Wayne State University, Detroit, Michigan
I. EICOSANOIDS
There is a complex relationship among dietary fats, eicosanoids, and the immune
system. Because long chain polyunsaturated fatty acids are the precursors for eicosanoids,
these dietary components have the potential to modify levels of the products
in the body. This is especially true if there is heavy reliance on a single fat in the
diet. While this is the standard approach in nutrition studies in animals, it is also
true that in a number of countries a single fat source provides as much as two-thirds
of the human population’s total fat intake. In controlled feeding trials in humans,
both the type and the amount of fat have been varied to permit an examination of
the effects on eicosanoid production or changes in immune status.
Eicosanoids are only one of many possible mediators through which diet can
influence the immune response. Eicosanoids are a large group of cyclized derivatives
of the essential fatty acids that have potent biological activities and always contain
20 carbon atoms. These compounds usually have very short half-lives (measured in
seconds) and are derived from the precursor fatty acids via a series of enzymatic
steps (Fig. 1). In addition to the prostaglandins and leukotrienes, a variety of derivatives
of 20-carbon fatty acids are produced. These include hydroxy and hydroperoxy
fatty acids as well as hydroxylated or epoxydized derivatives. Cyclooxygenases add
two oxygen molecules, lipoxygenase adds a single oxygen molecule, and cytochrome
P450s add one atom of oxygen to the fatty acid.
The principal characteristic of the essential fatty acids (EFAs) is the presence
of two or more cis double bonds in the families of �3 or�6 fatty acids, which must
be derived from the diet. Fatty acids containing trans double bonds do not have EFA
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.