Introduction: the history of lipids in human nutrition
The term “lipid” was introduced by Bloor in 1943, by which time the existence of cholesterol had been known for nearly 200 years and individual fats for 130 years. Cholesterol was named “cholesterine” (Greek for bile-solid) by Chevreul in 1816, although he did not discover it. Cholesterol’s association with aortic plaques dates at least to Vogel’s work in 1843. Chevreul isolated a mixture of 16- to 18-carbon saturated fatty acids in 1813 that was called margarine because he thought it was a single 17-carbon fatty acid, marga-rate. The mixed triacylglycerol (TAG) of palmitate (16:0) and stearate (18:0) was also called margarine, whereas the triglyceride of oleate, stearate, and palmi-tate became known as oleomargarine. Phospholipids were discovered by Thudicum, who isolated and named sphingosine in 1884 and also lecithin (phos-phatidylcholine) and kephalin (phosphatidylethanol-amine). The difference in polarity across phospholip-ids is a key attribute of these molecules and was termed “amphipathic” by Hartley in 1936 and renamed “amphiphilic” by Winsor in 1948.
The first understanding of how fat was absorbed emerged in 1879 when Munk studied fat emulsions and showed that lymph contained TAG after a fatty meal, and even after a meal not containing TAG. In 1905, Knoop deduced that fatty acid β-oxidation probably occurred by stepwise removal of two carbons from the fatty acid. The probable role of two carbon units as building blocks in the synthesis of fatty acids was recognized by Raper in 1907, but it took until the 1940s for Schoenheimer, Rittenberg, Bloch, and others to confirm this, using tracers such as deuterated water and carbon-13. The late 1940s was a seminal period in our understanding of how fatty acid oxidation occurs. Green and colleagues discovered that ketones were fatty acid oxidation products, and Lehninger demonstrated the role of mitochondria as the cellular site of fatty acid oxidation. Microsomal desaturases were shown to introduce an unsaturated bond into long-chain fatty acids by Bloomfield and Bloch in 1960.
In 1929, Mildred and George Burr discovered that the absence of fat in a diet otherwise believed to contain all essential nutrients impaired growth and caused hair loss and scaling of the skin of rats. This led to the isolation of the two primary “essential” polyunsaturated fatty acids, linoleate (18:2n-6) and α-linolenate (18:3n-3). The prostaglandins are a sub-class of eicosanoids that were discovered in the early 1930s by Von Euler, who mistakenly believed that they originated from the prostate gland. The link between the eicosanoids and polyunsaturates, principally arachidonate, was established in the 1960s.
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