Fats

Fats, oils, waxes, and sterols are collectively known as lipids. The broad class of substances known as fats don't have a common structure, but can be generally classified as esters of fatty acids and glycerol. There can be one to three ester linkages of fatty acid chains to the glycerol, leading to the classification as monoglycerides, diglycerides and triglycerides. Sometimes the use of the word "fat" is limited to the triglycerides. The term fatty acid is a substructure of the lipids, and should not be used as a synonym for "fat".

Naturally occurring fatty acids nearly always have an even number of carbon atoms.

Saturated Fats

A fully saturated fat has no double bonds between the carbons in its fatty acid chains. Generally speaking, animal fats are more highly saturated than vegetable fats. Highly saturated fats are usually solid at room temperature.

Unsaturated Fats

A fully saturated fat has no double bonds between the carbons in its fatty acid chains. If there are many double bonds in the fatty acids, then usually the fat will be liquid and will be called an oil. Most oils are of vegetable origin. The term "polyunsaturated fat" will also be used to describe such fats.

Trans fat is the common name for a type of unsaturated fat with trans-isomer fatty acids. Most trans fats consumed today are created industrially in partial hydrogenation of plant oils - a process developed in the early 1900s and first commercialized as Crisco in 1911. The goal of partial hydrogenation is to add hydrogen atoms to cis-unsaturated fats, making them more saturated. These saturated fats have a higher melting point, which makes them attractive for baking and extends their shelf-life. Trans fats are not essential in the diet and have been linked with rises in levels of "bad" LDL cholesterol and lowering levels of "good" HDL cholesterol.