Novel Triglycerides for Special Medical Purposes

The clinical use of intravenous lipid emulsions have been routine for over 25 years. For most of that time period the use of the vegetable oils, soybean and safflower, were the exclusive lipid source for these emulsions. Recently intravenous medium‐chain triglycerides have been commercially available. This review will discuss several important new research developments coming from the laboratory which should prove to enhance the nutritional effectiveness as well as minimize the adverse effects of lipid emulsions. The use of medium‐chain triglycerides either enterally or parenterally has shown them to be superior energy sources when compared to long‐chain triglycerides. Under experimental conditions of burn injury, their support of certain aspects of protein metabolism is superior to that of the current emulsions. This may be due to their rapid and preferential oxidation and poor storage into adipose tissue, and increased thermogenesis which has been observed from either enteral or parenteral administration in humans. This increased metabolic rate is not accompanied by an increase in temperature. Lipid emulsions have been described as having many different effects on variable aspects of the immunologic system. Some of these could be considered to be beneficial or without harm, and others are considered potentially deleterious. We have focused on the effects of parenteral lipid emulsions, in animals as well as in humans, on the function of the reticuloendothelial system. Compared to long‐chain triglyceride emulsions, those made from medium‐chain triglycerides, either as physical mixes with a small amount of long‐chain triglyceride or as chemically structured triglycerides, have been shown not to impact adversely on reticuloendothelial system function. In a series of clinical studies, we have shown impairment of the reticuloendothelial system after 3 days of an intravenous soybean oil emulsion when it is given for 10 hr whereas no impairment was seen if the emulsion is given either for one day, 3 days continuously (24 hr/day), or when the emulsion predominantly consisted of medium‐chain triglycerides. Besides being a superior energy substrate which does not interfere with the reticuloendothelial system, new types of triglycerides have been shown to actually change the metabolic response to injury or infection. Besides the above mentioned increase in metabolic rate when one feeds medium‐chain triglycerides, we have shown a blunting of a recombinant interleukin‐1‐induced fever in animals previously fed fish oil. Additionally, improved survival following endotoxin administration in guinea pigs fed either orally or parenterally diets containing fish oil, has been shown. A possible mechanism for this is a less severe metabolic acidosis produced after endotoxin administration in those animals fed fish oil. The continual exploration of these different lipid sources to be given as potential parenteral emulsions to hospitalized patients will provide significant improvements in our current nutritional delivery and clinical care. (Journal of Parenteral and Enteral Nutrition12:127S‐132S, 1988)