Routine use of parenteral lipid emulsions (LE) in clinical practice began in 1961, with the development of soybean oil (SO) - based LE. Although clinically safe, experimental reports indicated that SO-based LE could exert a negative influence on immunological functions. Those findings were related to its absolute and relative excess of omega-6 polyunsaturated fatty acids (PUFA) and the low amount of omega-3 PUFA and also to its high PUFA content with an increased peroxidation risk. This motivated the development of new LE basically designed along the reduction of omega-6 PUFA and the omega-3 PUFA addition in order to obtain balanced levels of the omega-6/omega-3 ratio. The new LE for clinical use (available in Europe and South America) are differentiated by their content in polyunsaturated (omega-6 and omega-3), monounsaturated, and saturated fatty acids (FA), as well as FA source of their origin, including soy, coconut, olive, and fish oil. This article presents the new LE nutrition and energy functions but also its biochemical, metabolic, and immunomodulating aspects, according to their FA content. LE at 20% when infused from 1.0 to 2.0 g/kg body weight/day rates, either alone or in association with amino acids and glucose, are safe and well tolerated in routine clinical practice. LE combining SO with medium-chain triglycerides and/or olive oil have less omega-6 PUFA and are better metabolized, with less inflammatory and immunosuppressive effects than in relation to pure SO-based LE. The omega-3 PUFA used alone or as component of a new and complex LE (soy, MCT, olive and fish oil) has demonstrated anti-inflammatory and immunomodulatory effects.