Triglyceride

A triglyceride, also called a triacylglycerol, is the chemical form of most fats and oils. It consists of glycerol, a small three-carbon alcohol, with a fatty acid attached to each of its three carbons by an ester bond; each bond forms in a dehydration reaction that gives off a molecule of water. The three fatty acids may be alike or different, and whether they are saturated or unsaturated decides much about the fat. Straight saturated chains pack tightly into solids such as butter, while kinked unsaturated chains give liquid oils.

Triglycerides are a compact energy store, holding more than twice as much energy per gram as carbohydrate or protein. The body takes them in from food and also makes them in the liver from surplus carbohydrate, then stores them in fat cells called adipocytes. Since they do not dissolve in water, they travel in the blood inside lipoprotein particles: chylomicrons carry fat absorbed from the gut, and very-low-density lipoproteins (VLDL) carry fat made by the liver. When energy is needed, enzymes called lipases split them back into glycerol and fatty acids, which are then burned for fuel.

A routine lipid panel measures blood triglycerides alongside cholesterol. Raised levels are linked with heart disease and metabolic syndrome, and very high levels can inflame the pancreas.