An update on parenteral lipids and immune function: only smoke, or is there any fire?

Purpose of review This paper synthesizes information from recent studies on the modulation of immune responses by lipid emulsions that are applied as part of parenteral nutrition. This issue is especially relevant in light of the high rate of infectious complications and disturbed inflammatory responses in patients receiving this form of nutritional support. Recent findings Studies reporting on novel emulsions based on olive and fish oils, structured lipids or mixed-type emulsions in which various lipid species replace conventional long-chain triglycerides indicate that these lipids are generally well tolerated. While long-chain triglycerides may promote inflammation due to conversion of n-6 polyunsaturated fatty acids into arachidonic acid-derived eicosanoids, structured lipids and olive oil emulsions appear more immune-neutral. Leukocyte-activating effects of medium-chain triglycerides in experimental studies await further characterization in vivo. A body of evidence shows that immune modulation by fish oil emulsions is essentially anti-inflammatory in nature. This is in line with the observation that n-3 polyunsaturated fatty acids in fish oil replace arachidonic acid in cell membranes as an eicosanoid substrate, resulting in a decreased production of proinflammatory mediators. Importantly, recent investigations indicate beneficial effects of parenteral fish oil on relevant clinical outcome measures. Summary The characteristics of, and mechanisms behind, the effects of various parenteral lipids on immune function are becoming increasingly well understood. The practical relevance of many of these findings is not immediately clear, however, and will have to be substantiated in adequately powered trials before we can translate these findings into a tailored approach for specific clinical situations.