hello Lactnetters. I am new to Lact net and want to respond to this question though I suspect there are others with more thorough knowledge. To introduce myself, I have had a long standing interest in lactation having been a LLL Leader about 20 years ago and and done some lactation research. I am privileged to serve on the Advisory board for LLLI and as the Liaison with LLLI for the ADA Perinatal Nutrition Practice group and am on the NPA Board. I am an RD faculty member at Ball State University and the Dean for Continuing Education. I teach a graduate course in Maternal and Infant Nutrition. Lipids are such an important source of energy to the grapidly growing infant and are very well absorbed from human milk. It is my understanding that cow milk fat is not well absorbed so loss of calories could interfer with growth. In an effort to improve fat absorbtion vegetable fats are substituted because the longchain polyunsaturated fatty acids are quite well absorbed and provide significant energy. I believe aconsiderable part of this research was done by Dr. Filer who has worked with Dr. Fomon's group in Iowa. The vegetable lipids do not provide the very longchain polyunsaturated fats found in human milk and thought to be beneficial to central nervous system development, especially important in the preterm infant. Particular interest currently centers on lipids such as DHA -docosahexaenoic acid, which is thought to be critical to CNS development and is found in human milk.