Lipids are important both for caloric content but also to provide essential
fatty acids. The two essential fatty acids are alpha-linolenic acid (ALA, omega 3
fatty acid) and linoleic acid (LA, omega 6 fatty acid). The appropriate balance of
these two essential fatty acids is important for proper function of the multiple
dependent physiologic processes including inflammation, cell signaling and cell
wall structure. Omega 6 fatty acids (LA) are considered pro-inflammatory
(prostaglandin and arachidonic acid precursor), while Omega 3 (ALA) are
considered anti-inflammatory (docosahexaenoic acid precursor). The ratio of the
fatty acids is important because of competition by these two fatty acids for the
same enzymes in various physiologic processes. The omega 6 to omega 3
ratios found in the diet are usually very high with ratios of 10:1 or higher which is
markedly different from the 1:1 ratio assumed to occur in the diet of our
evolutionary ancestors. This presumed metabolic imbalance has been
implicated as promoting inflammation, thrombosis and vascular constriction
leading to a variety of chronic medical conditions. Intravenous lipid is frequently
from soybean oil with a ratio of 7:1. An inverse ratio of 1:4, emphasizing omega
3 fatty acids, has been suggested as an optimal ratio. Cold-water oily fish
including salmon, herring, mackerel and sardines have a ratio of 1:7. For this
reason, fish oil is under investigation as an alternative to soybean oil.
The most commonly utilized intravenous solution for lipid administration in
the USA is Intralipid®, which is made from soybean oil. Both the 10% and the