ABSTRACT
Classically, lipids have been defined as substances that are generally insoluble in water but soluble in organic solvents such as ether, acetone, and chloroform. There are a variety of different kinds of lipids applicable to human structure and function including fatty acids, triglycerides (triacylglycerols), phospholipids, and sterols (i.e., cholesterol). All too often lipids are viewed only from an energy perspective. For instance, fatty acids are oxidized to form ATP in almost all human cells and are the principal source of energy during periods of fasting. Furthermore, the storage of triglycerides, can represent as much as 90,000 to 100,000 kcal of energy for an average adult male. Further still, triglycerides, or more com monly, fat, account for as much as a third or more of the total energy consumed in many countries and is the focus of many body weight reduction efforts. However, to view lipids only from an energy perspective would greatly understate their unique properties and physiological significance. Body fat has excellent insulating properties, thereby guarding against heat loss. Also, body fat deposits provide internal padding to protect visceral organs. Dietary essential fatty acids (EFA), linoleic acid and linolenic acid, are converted into local-acting eicosanoid factors. These factors are fundamentally involved in the regu lation of numerous cellular and tissue operations such as blood pressure, platelet aggrega tion, bronchial constriction, chemotaxis, and inflammation. Diglycerides are the basis of phospholipids, which are the foundational component of cellular membranes and lipopro teins. Glycolipids and cholesterol are also key components of cell membrane. Cholesterol also serves as the precursor molecule for a variety of steroid molecules such as testosterone, DHEA, estrogens, cortisol, and aldosterone.
