ABSTRACT
There is no single, universally recognized definition of the term lipid, but it encompasses a range of molecules, including fatty acids and steroids, which are generally insoluble in water.
Lipids constitute approximately 20% of body weight in humans, mostly as an energy store (as triglyceride) in adipose tissue and as structural lipids (phospholipids) in cell membranes. The high energy yield from oxidation of fatty acidstwice that of carbohydrate-allows them to serve as the major respiratory substrate for most tissues apart from brain, nervous tissue, erythrocytes, and the kidney, and the movement of diet-derived triglyceride from the gut to adipose tissue, and of fatty acids from adipose tissue to other tissues, including liver, is essential for metabolic homeostasis. Increases in the concentration of blood lipids-measured in the clinical laboratory as cholesterol and triglycerides-may be features of pathological conditions, such as liver disease, hypothyroidism, and diabetes mellitus, and high concentrations of blood lipids are risk factors for the development of atherosclerosis.
