Omega 3 and 6 Fatty Acids
The essential fatty acids (
, omega 3 and omega 6) are
required for the production of eicosanoids.
Essential fatty acids are not made in the human body,
but can be converted to others in the same family (omega 3 and omega 6 are these families).
Eicosanoids are oxidized fatty acids with at least 20 carbons.
The pathways for their production
divide into prostaglandins (PG), thromboxanes (TXA) and leukotrienes (LT). PGs and TXA are
generated by a pathway called the cyclooxygenase pathway (inhibited by aspirin), while the LTs
are made by lipoxygenase.
There are involved in modulating cardiovascular, pulmonary, immune,
reproductive and secretory systems.
The physiological action of the eicosanoids depends on the family produced.
Fatty acids of 20
carbons with only 3 double bonds (C20:3, omega 6), result in PG1s and LT3, while those of 4
double bonds (C20:4, omega 6) go to PG2s, TX2 and LT4, and those of 5 double bonds (C20:5
omega 3) to PG3s, TX3 and LT5.
The basic starting material for the omega 6 family is
(18:2 omega 6). This can be
gamma linolenic acid
(C18:3, omega 6,
GLA can be elongated to the C20:3
Dihomo-gamma-linolenic acid (DHGLA). Linoleic acid and GLA are considered to be
essential fatty acids.
They are not made directly into eicosanoids, but do have physiological action
because it can be converted to dihomo-gamma-linolenic acid.
This reaction depends on the
amount of other PUFAs.
) the most common precursor to eicosanoids,
(C20:4 omega 6), is made from dihomo-gamma-linolenic.
It is found in the highest concentration in
animal and milk products and is present in very low amounts in most plants.
The omega 3 fatty acids have one 20 carbon fatty acid (eicosapentaenoic acid,
, C20:5) and
one common 22 carbon with six double bonds (C22:6, Docosahexanoic acid,
The omega 3
fatty acids can be derived from
alpha linolenic acid
, 18:3, omega 3).
All of the fatty acids affect the metabolism of the others, so an imbalance of either 18:3 can
reduce the amount of the other family (i.e., high intakes of fish oil with omega 3 will reduce the
amount of omega 6 eicosanoids).