Linoleic acid deficiency is associ
ated with growth deficiencies
and skin problems.
Linoleic acid is widespread in plants and seed oils; arachidonic
acid is found mainly in meats, egg yolk, and some fish. Alpha-Linolenic Acid
The only known function of alpha-linolenic acid is to serve as a
precursor for the synthesis of the long-chain omega-3 fatty acids, eicosapentaenoic acid and docosahexaenoic acid.
For detailed information, see
Omega-3 Fatty Acids
on page
81
.
Docosahexaenoic Acid
Docosahexaenoic acid is a conditionally essential nutrient. Its
production from alpha-linolenic aci
d may be inadequate to meet
needs for brain growth in early human development and it confers functional benefit even when alpha-linolenic acid is in the diet.
Both docosahexaenoic acid and arachidonic acid are available in
breast milk and in many infant formulas.
For detailed information, see
Omega-3 Fatty Acids
on page
81
.
Long-Chain Polyunsaturated Fatty Acids
Long-chain polyunsaturated acids have several roles:
-^
Oxidation to provide energy
-^
Triglyceride synthesis and limited tissue storage
-^
Phospholipids in membranes, particularly neural tissue
-^
Eicosanoid synthesis: prostaglandins, thromboxanes, leukotrienes
Membranes
As structural components of membranes, arachidonic acid and
docosahexaenoic acid influence the functional characteristics of tissues, particularly neural tissues.
Docosahexaenoic acid is concentrat
ed in the outer segment of
the rods in the retina of the ey
e. The presence of docosahexaenoic
acid is related to light activation and visual processing.
For detailed information, see
Omega-3 Fatty Acids
on page
81
.
Eicosanoids
Arachidonic acid is the major precursor for the synthesis of
eicosanoids, cellular regulatory substances and mediators of inflammation that include prostaglandins, thromboxanes, and leukotrienes.
Eicosanoids are involved in platelet aggregation, T-cell
proliferation, lymphocyte migrati
on, vasoconstriction and dilation,
and the production of several immune and inflammatory substances.
In the presence of eicosapentaenoic acid, eicosanoids derived
from the omega-3 family are also produced. These attenuate or inhibit the action of the arachidonic acid -derived eicosanoids. Those derived from eicosapentaenoic acid have weaker biological activity than those from arachidonic acid.
Competition from omega-3 fatty acids for the same eicosanoid
synthesizing enzymes may reduce the production of omega-6 eicosanoids.
Eicosapentaenoic acid can moderate the production and activity
of arachidonic acid–derived eicosanoids.
The predominance of eicosanoids derived from omega-6 fatty
acids may contribute to chronic diseases, including heart disease.
For detailed information, see
Omega-3 Fatty Acids
on page
81
.
Toxicity Cardiovascular Diseases
See
Heart-Healthy Fat
on page
87
.
Nutrition for Sports, Essentials of 80