Fats = Solid Fats + Liquid Oils

Fats and oils are composed of triacylglycerols or triglycerides in which three fatty acids—either an unsaturated or saturated fatty acid, or both—are attached to an alcohol molecule called glycerol. Solid fats have a higher proportion of saturated fatty acids, which makes them behave like solids at room temperature; oils are richer in unsaturated fatty acids, which makes them behave like liquids at room temperature. Of the unsaturated fatty acids, the monounsaturated fatty acids (MUFAs) are relatively stable to oxidation, take a longer time to turn rancid, and are considered healthier (for example, olive oil is rich in MUFAs). The second type of unsaturated fatty acids is the polyunsaturated fatty acids (PUFAs), which are unstable; these include the omega-6 and omega-3 fatty acids (see Lipids).