Vegetable oils have been used both enterally and parenterally for many years. This experience has helped identify the various benefits and risks associated with their use. Newer lipids have been developed to substitute for the presently available ones. Among the newer generations of lipids are medium-chain triglycerides, structured triglycerides, and ω3 polyunsaturated fatty acids. These lipids are a good source of calories and play a role in modifying patients' metabolic responses to disease in a favorable manner. Medium-chain triglycerides are oxidized better than long-chain triglycerides, with very little stored as fat. Unlike long-chain triglyceride emulsions, they minimally interfere with immune function as measured by reticulo-endothelial system uptake. The ω3 polyunsaturated fatty acids, which are found in large quantities in fish oil, have shown benefit in many clinical situations. Hypotriglyceridemia, increased high-density lipoprotein levels, decreased platelet aggregability, and blood pressure control seem to be beneficial in cerebral and cardiovascular disease. Because of their ability to incorporate into cell membranes and alter eicosanoid metabolism, they seem to play a role in immunomodulation and attenuating the body's response to overwhelming sepsis.