Food Lipids: Chemistry, Nutrition, and Biotechnology

18
Unsaturated Fatty Acids
STEVEN M. WATKINS
Lipomics Technologies, Inc., West Sacramento, California
J. BRUCE GERMAN
University of California, Davis, California
I. INTRODUCTION
Fatty acids serve a wide variety of metabolic functions critical to all forms of life.
They are a rich source of energy and carbon and well designed as a convenient unit
for energy storage. However, the importance of fatty acids in human nutrition and
physiology goes well beyond their role as a source of calories. Fatty acids provide
the structure and hydrophobicity crucial to the maintenance of a semipermeable
membrane barrier. Their structures can be modified by desaturation and elongation
to produce a substantial variety of species with individual chemical and physical
properties. Ester linkages to glycerides allow fatty acids to be easily exchanged for
one another and allow cells to manipulate the physical properties of their membranes.
Fatty acids also serve as precursors to active signal molecules such as eicosanoids,
which are capable of producing potent biological effects. Evolution has produced a
distinction between plants and animals in their capabilities for the metabolism of
fatty acids. Higher animals are unable to synthesize all of the fatty acids required
for certain tissue functions and are obligated to ingest fatty acids that are synthesized
by plants. Animals have evolved a separate and distinct series of metabolic modifications
of fatty acids, but are still unable to alter the original modifications inserted
by plants. As a result, the membrane, signal, and storage lipids of animals vary
widely according to their dietary intakes. In addition, the ability of an animal to
produce a specific fatty acid relies either on an inherent mechanism for desaturation
of saturated fatty acids or on the ingestion of a convertible precursor. The ingestion
and/or metabolism of particular unsaturated fatty acids is necessary for a great variety
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.