The history of the scientific documentation of the need for fat in the diet began with the early nineteenth-century work of Michel Eugene Chevreul (Mayer and Hanson 1960). He showed that lard contained a solid fat, which he termed stearine, and a liquid fat he called elaine (later shown to be the isomer of oleine), and in 1823, this work was published in a treatise, Chemical Investigations of Fats of Animal Origin. Chevreul also crystallized potassium stearate, naming it ‘mother-of-pearl’ and calling its acidified product “margarine” (from the Greek word for mother-of-pearl). In addition, Chevreul isolated various acids from fats and distinguished them on the basis of their melting points.

Meanwhile in 1822, Edmund Davy had reported that iodine would react with fats, and by the end of the century, work by L. H. Mills and Baron Hubl led to the procedure devised by J.J.A. Wijs in 1898 for determining a fat’s “iodine value” or “iodine number” – a measure of the extent to which a fat is unsaturated, based on its uptake of iodine. Highly saturated coconut oil, for example, has an iodine number of 8 to 10, whereas that of highly unsaturated linseed oil ranges from 170 to 202.

Phospholipids were described in 1846 by N. T. Gobley, who found that egg yolk had a substance that contained nitrogen and phosphorus in addition to glycerol and fatty acids. He named it lecithin. The nitrogenous base was shown to be choline by A. Strecker in 1868, and J.W. L. Thudichem described kephalin in 1884 (Mayer and Hanson 1960).