Notice that some of the fatty acids are called saturated fatty acids and others are called unsaturated fatty acids. If a carbon atom is attached to four other atoms by single bonds it is known as a saturated carbon atom. However, a carbon atom can be attached to fewer than four other atoms, but still have four bonds to it. The carbon could be part of a double bond, where it is attached to only three other atoms. In such cases the carbon is known as an unsaturated carbon atom.

Each of the carbon atoms in the hydrocarbon chains is attached to four other atoms by single bonds. Thus, they are all saturated chains.

Acids such as palmitic and stearic are known as saturated fatty acids, and the triglycerides made from them give rise to saturated fats. Note that, using this nomenclature, we examine only the chains. The unsaturated carbon atom in the functional group is not considered. Oleic acid has one double bond in its hydrocarbon chain. The carbon atoms of this double bond are attached to only three other atoms and are thus unsaturated. Oleic acid is therefore known as a monounsaturated fatty acid. Linoleic acid contains two double bonds in its hydrocarbon chain and is known as a polyunsaturated fatty acid or PUFA. Any fatty acid containing two or more double bonds in its hydrocarbon chain is a PUFA.

Because the continuing chains attached to the two carbon atoms of the double bond are on the same side of the double bond, this is a cis compound. In fact, in this case, it is easier to look at the disposition of the hydrogens on the double bond. In cis compounds they are on the same side, whereas in trans compounds they are on opposite sides.

Most fatty acids in nature involve cis rather than trans double bonds.

The figure here shows the range of fatty acids that lead to the triglyceride molecules that make up a particular fat or oil. The data are presented as a series of histograms, where the relative heights of bands reflect the percentage composition of the different fatty acids that are used to make the fat. The percentages are based on the relative numbers of molecules of each of the fatty acids. Fats are an essential part of the diet, but, as we saw earlier, there have been recommendations that we should eat less fat in general, but in particular we should eat less fat derived from saturated fatty acids.

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