Fatty acids, lipid emulsions and the immune and inflammatory systems

Fatty acids modulate the responses of cells of the immune system. Inflammatory and immune responses in patients receiving parenteral nutrition may be modulated by the type of lipid used, which may influence clinical outcomes. Lipid emulsions based solely upon soybean oil may not be optimal because of the role of n-6 fatty acids in promoting inflammation and suppressing immune responses. Lipid emulsions with soybean oil in various combinations with medium-chain triglycerides (MCTs), olive oil and fish oil are available. Some early studies have suggested better immune function with MCT-soybean oil than with soybean oil alone, but the differences were small, and more recent studies suggested little difference between soybean oil, MCT-soybean oil and soybean oil-olive oil regarding markers of inflammation and immunity. The inclusion of fish oil in combination with one or more other oils (i.e. soybean, MCT, olive) in the parenteral regimen administered to patients following major gastrointestinal surgery reduces the post-surgery rise in inflammatory markers and the fall in cell-mediated immune markers. These changes are associated with improvements in clinical outcomes. Whether similar effects of intravenous fish oil occur in critically ill patients is not clear at present because of the small number, small size and variable findings of existing studies. The lipid component of parenteral nutrition may modify inflammatory and immune processes in ways that influence patient outcome. The inclusion of fish oil in parenteral nutrition for post-surgical patients is associated with benefits. The situation regarding critically ill patients is not clear.