The Fats of Life: Essential Fatty Acids in Health and Disease

3. Some Dietary Fats are Essential

The idea that certain foods contain substances that relieve the symptoms of what we recognize today as vitamin deficiencies dates back to ancient times. An Egyptian papyrus (Eber’s Papyrus) containing a medical treatise dating to about 1500 B.C.E. recommends eating liver to cure the condition of night blindness . We know today that night blindness is caused by a deficiency of vitamin A and that liver is a good source of this vitamin. The famous Greek philosopher Hippocrates, who lived around 400 B.C.E., prescribed ox liver to cure night blindness (Liu and Roels 1980). Eber’s Papyrus also describes the disease that we now know as scurvy, although little was known about its cure at that time. Scurvy was a serious problem for naval crews during the period of great global explorations, because the sailors would be at sea, often for months, without fresh fruits or vegetables. The Chinese were well aware of scurvy, and their ships plying the seas in the late fourteenth and early fifteenth centuries grew soybeans in tubs, which provided sprouts that had ample amounts of vitamins, including vitamin C (Menzies 2003). The French explorer Jacques Cartier lost many of his crew along the St. Lawrence River in what is now Quebec in the winter of 1535–1536 when they fell ill with scurvy. The local natives brewed an extract from an evergreen (white cedar) tree that cured the survivors (Pauling 1970). The tree became known as arborvitae (Latin for tree of life) and is now a popular landscaping tree in suburban North America. Sir Richard Hawkins, a sixteenth-century British admiral, described the use of oranges and lemons in treating British sailors who had scurvy. A later treatise by the Scottish naval surgeon James Lind, in 1753, is probably responsible for bringing this latter cure to the attention of a much wider audience, including the medical profession. British sailors became known as limeys during the nineteenth century because they were required to drink lime juice to ward off scurvy. The active component in citrus fruits was referred to as ascorbutic 3 Some Dietary Fats Are Essential 33 NUTRITIONAL, CHEMICAL, AND PHYSIOLOGICAL PROPERTIES 34 factor (scorbutic meaning related to scurvy and the a- prefix meaning without), and when it was finally isolated and its chemical structure determined by Albert Szent-Gyorgi in 1935, it was named ascorbic acid (Pauling 1970). Many different organic (or plant-derived) substances were identified as being essential, although the chemical compositions of the essential components were not identified until the twentieth century. Most were chemically classified as amines because they contained the element nitrogen and were vital for human health, ergo the term vitamine. Later, when it was discovered that not all contained nitrogen, and consequently were not amines, it was perhaps deemed simpler to drop the final “e” rather than coin a new term. In 1929 George and Mildred Burr reported that they could induce a deficiency syndrome in laboratory rats by the rigorous exclusion of fat from their diets (Burr and Burr 1929). The deficient rats showed abnormal growth and developed skin disorders, such as lesions on their tails, dandruff, loss of hair, and abnormal appearance. There were disturbances in ovulation in females and prolapsed penises in males. It was also believed, because of bloody urine, that the deficiency resulted in kidney degeneration. Adding small amounts of lard to the diet cured the deficiency syndrome, as did a small amount of liver. The researchers later tested specific fatty acids and found that adding linoleic acid or arachidonic acid (two omega-6 polyunsaturated fatty acids) to the diets would relieve the deficiency symptoms (Burr and Burr 1930). It was also found that linolenic acid, an omega-3 polyunsaturated fatty acid, could restore normal growth but did not alleviate the skin disorders. It was concluded that these three polyunsaturated fatty acids were essential in the diet and the body could not make them. In the 1950s James Mead and coworkers at University of California, Los Angeles, worked out a metabolic pathway for the conversion of linoleic acid to arachidonic acid in humans (see figure 2.4, previous chapter). It was recognized that arachidonic acid was not essential in the diet if linoleic acid was provided (Steinberg et al. 1956). Consequently, some nutritionists chose to eliminate arachidonic acid as an essential fatty acid, leaving linoleic and linolenic acids as the only two essential fatty acids. The...