ABSTRACT
Sterols are minor constituents present in the fat of the human diet. They comprise the major portion of the unsaponifiable fraction of most edible fats and oils. Sterols can be classified according to their origin as animal sterols or as plant sterols. The latter can be subdivided into phytosterols (higher plant sterols) and mycosterols (lower plant sterols present in the lipid fraction of yeast and fungi). Cholesterol is the main animal sterol, while sitosterol, campesterol, and stigmasterol are the major plant sterols. These phytosterols and cholesterol are all 4-desmethylsterols that share identical ring structures. The various sterols differ only in their side chains. Surprisingly, these minor differences result in major changes in their biological functions. They are widely distributed in nature, and occur both in the free form or combined, most frequently as esters of higher aliphatic acids and glycosides. Sterols, sterol esters, and sterol glycosides are, to different degrees, soluble in fats but completely insoluble in water.
