Discovery of essential fatty acids

Abstract

Dietary fat was recognized as a good source of energy and fat-soluble vitamins by the first part of the 20th century, but fatty acids were not considered to be essential nutrients because they could be synthesized from dietary carbohydrate. This well-established view was challenged in 1929 by George and Mildred Burr who reported that dietary fatty acid was required to prevent a deficiency disease that occurred in rats fed a fat-free diet. They concluded that fatty acids were essential nutrients and showed that linoleic acid prevented the disease and is an essential fatty acid. The Burrs surmised that other unsaturated fatty acids were essential and subsequently demonstrated that linolenic acid, the omega-3 fatty acid analog of linoleic acid, is also an essential fatty acid. The discovery of essential fatty acids was a paradigm-changing finding, and it is now considered to be one of the landmark discoveries in lipid research.

Keywords: arachidonic acid; docosahexaenoic acid; eicosapentaenoic acid; fat-soluble vitamins; linoleic acid; prostaglandins; α-linolenic acid.

Fig. 1.

George Oswald Burr. Reprinted from Smithsonian Institution Archives (SIA2008-0081) (http://siarchives.si.edu) with permission.

Fig. 2.

Data from Burr’s 1929 paper demonstrating the essentiality of fatty acid. The saponifiable (fatty acid) fraction of lard stimulated growth of rats when added to a fat-free diet (left set of data), but the nonsaponifiable lipids (middle set), and glycerol (right set) did not. Each line represents data from a single rat, and the time interval between data points is 4 weeks. Reprinted with permission from (1).

Fig. 3.

Data from Burr’s 1930 paper demonstrating that linoleic acid is an essential fatty acid. Lipids that contain linoleic acid, especially linseed oil, corn oil and poppy seed oil which have a high percentage of linoleic acid, and methyl linoleate, stimulated the growth of rats when added to the fat-free diet, whereas coconut oil which is highly saturated and methyl stearate did not. While methyl oleate also stimulated growth in this study, subsequent work did not substantiate this finding (see Fig. 4). Each line represents data from a single rat, and the time interval in days is indicated by the size of the double-headed arrow at the bottom of each figure. Reprinted with permission from (2).

Fig. 4.

Data from Burr’s 1932 paper demonstrating that α-linolenic acid is an essential fatty acid. Methyl linolenate stimulated the growth of rats on a fat-free diet (right side), while methyl oleate did not (left side). Each line represents data taken from a single rat, and the time interval of each horizontal segment of the grid is 10 days. Reprinted with permission from (31).