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In the past, dietary fats got bad press. There was a deeply rooted belief that they were basically unhealthy, were useful at best as an energy store for hard times, and had one purpose only—to keep the body supplied with fuel for energy. This view is not completely wrong; about 80% of ingested fat, and the saturated and unsaturated fatty acids it contains, is stored in special cells and burnt up as required. However, there is more to fats than that. Some fats and fatty acids have specific physiologic roles to play.
The nutritional importance of specific lipid molecules in fat was first revealed through the pioneering work of George and Mildred Burr in the late 1920s (1). When weanling rats were fed a fat-free diet, the Burrs observed retarded growth, scaly skin, tail necrosis, impaired fertility, increased water consumption, and diminished urine production. They found that either linoleic or -linolenic acid—both polyunsaturated fatty acids (PUFAs)—was able to provide the missing factor. It was the era of the discovery of essential nutritional factors. Therefore, the active substance in fat was considered to be a new vitamin and, because the previous vitamin found was called vitamin E, was given the name vitamin F.
It is more than a mere coincidence that vitamins E and F were discovered almost simultaneously. In vegetable and animal oils and fats, the occurrences of vitamins F and E are invariably linked to one another; the higher the concentration of PUFAs, the higher the content of vitamin E. We now know the reason for this close association. Vitamin E functions specifically as an antioxidant for PUFAs. It protects the labile double bonds in PUFAs from oxidization.
Strangely enough, even though they were discovered almost simultaneously, the fate of the 2 vitamins took different courses. Whereas vitamin E soon became an accepted factor for human health and is a perpetual favorite of the news media, the term vitamin F disappeared into oblivion. The medical profession doubted that essential fatty acids had any relevance to humans, and the view that certain fatty acids could be essential components of the human diet never really captured the minds of the broader public.
It was difficult to produce clear deficiency symptoms in humans. The first experiments in humans consuming an extremely low-fat diet for 6 mo were unable to reproduce the abnormalities seen in several species of animals maintained on diets deficient in essential fatty acids; therefore, the essentiality of these fatty acids, at least in adults, was in question. In hindsight this was not surprising because the body of an adult human contains 1 kg linoleic acid, which takes much longer than 6 mo to be depleted.
It was 20 y later that Hansen et al (2) described severe skin symptoms in infants who had been fed a milk-based formula in which PUFAs were essentially absent. This work proved conclusively that linoleic acid was required for proper growth and health in infants. In 1982, Holman et al (3) described the first case involving specific symptoms due to -linolenic acid deficiency in a 6-y-old girl.
Although known to occur, at least in small amounts, in almost all biological lipids, PUFAs had no apparent biochemical function. It was not until the 1960s that it was discovered how closely the metabolisms of essential fatty acids and eicosanoids are related. We know today that some of the highly unsaturated fatty acids serve as the precursors of prostaglandins, thromboxanes, and leukotrienes—all highly potent, short-lived molecules with greatly diverse activities. This function of some long-chain fatty acids seemed to be of little relevance to human health until the work of Dyerberg, Bang, and Hjorne (4) in Eskimos sparked an entire field of research into the health effects of the n–3 long-chain PUFAs. In their epidemiologic studies of Eskimos living in Greenland, these 3 Danish scientists showed that this population group had one-eighth the risk of dying from cardiovascular disease that Eskimos who emigrated to Denmark had. The plausible explanation of the phenomenon was that the traditional diet of Greenland Eskimos is rich in two n–3 long-chain PUFAs, eicosapentaenoic (20:5n–3) and docosahexaenoic (22:6n–3) acids, which give rise to eicosanoids of antithrombotic potential. This pioneering work stimulated research worldwide, with the result that the potential role and mechanism of action of highly unsaturated fatty acids in prevention and therapy has become a major area of international research.
The combined results from epidemiologic, animal, and clinical studies in these lipids suggest that we may be dealing with a new class of micronutrients. The brain and nerve development of growing fetuses and newborns depend critically on the presence of arachidonic and docosahexaenoic acids, and highly unsaturated fatty acids may be a factor in the development and the severity of some degenerative disorders, ie, cardiovascular disease and conditions with an immunoinflammatory component, and of brain function disturbances and some forms of cancer.
Despite these intense research efforts, we are far from reaching a consensus on many issues. Many claims have yet to stand the test of rigid scientific proof. We are still struggling to make specific dietary recommendations with regard to highly unsaturated fatty acids, and it must be difficult for any individual to deal with the often contradictory information presented to him or her through the scientific media and the lay press.
To provide both factual information on the current state of research into highly unsaturated fatty acids and better guidance as to what constitutes a healthy diet, scientists, health professionals, and representatives from the industry and the media from all over the world gathered in Barcelona in 1996 to hold a conference titled Highly Unsaturated Fatty Acids in Nutrition and Disease Prevention under the motto "Fats of Life." I thank the many outstanding experts who lectured on the role of highly unsaturated fatty acids in infant nutrition, brain function, skin health, and inflammatory and cardiovascular disease. Also, thanks to the many contributions from the audience, more than 400 participants left with a better understanding of the dietary importance of this class of lipids.
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