|Food and Nutrition Bulletin Volume 14, Number 2, 1992 (UNU, 1992, 84 pages)|
|News and notes|
David M. Klurfeld
The article by Dupont et al.  addresses the effects of saturated and hydrogenated fats on health and reflects the prevailing opinion that a decrease in saturated fat intake, indicated primarily for lowering serum cholesterol levels. is warranted. In reviewing the multiple facets of this issue, Dupont et al. touch on the tropical oils controversy, which has become a significant consumer nutrition issue of the last few years. Major corporations scrambled to reformulate products so that specific fats were removed from the ingredients statement, while denying there was any scientific justification for this.
To understand the tropical oils question, one must first remember what is behind this name. There are no legal or scientific definitions of tropical oils. This was a term created by the American Soybean Association (ASA) as part of a public relations campaign in a trade war with the producers of palm oil. However. in common use the term refers to palm, palm kernel, and coconut oils. Cocoa butter, another oil exclusively of tropical origin, is never included in this definition, and many other oils, including soybean oil, are produced in tropical regions of the world. The term was coined after a proposal in a US congressional bill had been scuttled which would have identified fats on food labels with the descriptor 'saturated fat" if they contained more than 50% saturated fatty acid (SFA); the plan was scrapped when it was realized that this included butter and would hurt US farmers. The public and, unfortunately, many nutritionists do not make any distinctions among the three so-called tropical oils.
Palm oil is about 49% saturated (and, therefore, 51% unsaturated) and composed of 44% palmitic. 37% oleic. 9% linoleic, and 4% stearic acids. Palm kernel oil is about 81"/o saturated and contains 47% lauric, 16% myristic acid, 8% palmitic, and 11% oleic acids. Coconut oil is 87% saturated and contains 45% lauric, 17% myristic, 8% palmitic, and 6% oleic acids . The differentiation by degree of unsaturation and fatty acid (FA) chain length makes palm oil unique from the other two fats from both the perspectives of health and functionality in food processing. In fact, the original Hegsted formula for predicting serum cholesterol in response to dietary fat attributed the highest risk specifically to myristic acid; this equation suggested that myristic acid possessed more than two-thirds of diet's effect on serum cholesterol . The assumption in the review by Dupont et al. - "As palmitic acid is much more abundant than lauric and myristic acids in the usual western diets this SFA may be the primary contributor to the effect of dietary fat on the serum cholesterol in man" - is not supported by the Hegsted equation or by a number of recent studies. Hayes et al. [4, 5] have found that palmitic acid is neutral with respect to serum cholesterol levels in three species of non-human primates, that myristic and to a lesser extent lauric acid are hypercholesterolaemic, and that palmitic acid increases high-density-lipoprotein cholesterol and hepatic mRNA for apoA-I. Rudel et al.  recently reported that monkeys fed palm oil in a very high cholesterol diet became hypercholesterolaemic, but when cholesterol was omitted from the diets, the animals rapidly became normocholesterolaemic. Human populations that consume the most palm oil in the world are in Nigeria and Costa Rica. Both countries have a low total fat intake, serum cholesterol and apoB levels are low by Western standards, and heart disease is much less prevalent .
Perhaps the most relevant point in this entire debate is how little of any of these tropical oils is actually consumed by the US consumer. A recent estimate of average consumption indicates that all three oils combined provide <2% of total energy . Complete replacement of these oils with any highly unsaturated oil would probably have no measurable effect on serum cholesterol. Palm oil is used in commercial baking because of its high palmitic acid content, which leads to ß crystal formation, subsequent flaky pie crusts, and other desirable characteristics in foods. In their section on cooking oils, Dupont et al. describe desirable characteristics of frying oils, among which is oxidative stability - an attribute of palm oil due both to the FA composition and the minor components, the tocotrienols, which are potent antioxidants. The issue of oxidation is especially important in situations where oil is reused for frying, as in commercial operations and in poor areas of the world. Food uses of palm kernel and coconut oils are primarily in the confectionery business because of their low melting points and proper mouth feel. An important question touched on in the review is what might replace more highly saturated fats in the diet. Although soybean and canola oils are two of the more common replacements, 60% to 70% of the total production of these fats is hydrogenated for use in processed foods. This is done. in part, to give functional characteristics similar to palm and the other oils. When marketed as the pure oils. canola is unhydrogenated and soybean is usually partially hydrogenated. Analyses in the author's laboratory established that products fried in hydrogenated oils have a combined saturated and bans FA content equivalent to the saturated fat content of foods fried in palm oil. Dupont et al. conclude that "substitution of fats hydrogenated to contain bans FA for fats high in SFA may not be beneficial to health."
A major impact of the tropical oils issue is that it has engendered a classic example of the 'good food-bad food" dichotomy. Individuals with elevated serum cholesterol, who should make changes in their diet and a variety of other risk factors, are given false security by eliminating a few processed foods containing tropical oils. People are likewise given the impression that, once another oil is substituted for the offending tropical oil, the food in question becomes healthful even if it is still high in fat and calories. One illuminating example is how ice cream has been treated by those involved in this brouhaha. One serving of ice cream has several times the saturated fat content of any processed food made with palm oil (including doughnuts, cookies, crackers, layer cakes, etc.), yet none of the principals in this debate mention this all American dessert as a significant source of saturated fat that should be reduced. It was primarily the ASA and the Center for Science in the Public Interest that took up this issue, but with little impact until a wealthy man, who started his own foundation called the National Heart Savers Foundation, ran full-page newspaper advertisements singling out companies that were "poisoning America." This individual had neither credentials nor nutrition expertise to make this judgement, but the publicity caused sales of specific food products to drop, and processors removed oils termed tropical from foods.
Americans overindulge in total energy. fat, and saturated fat, but the impact of tropical oils on our diet is minimal. It is unlikely that complete substitution of unhydrogenated seed oils for these oils could have a measurable effect on serum cholesterol levels. However, the impact on nutrition in the developing countries is not to be taken lightly. Palm oil exports to the United States constitute only 3% of the world market for palm oil, and a substantial portion of that goes to non-food uses such as oleochemicals. But adverse publicity from the United States has caused many countries to question the safety of palm oil, which is the number-one oil of international trade and is second in production in the world.
Nutritionists around the world are questioning the safety of palm oil due to the adverse publicity in this country. Even in countries with heart disease prevalence half that in the United States and where serum cholesterol concentrations are low by Western standards such as Costa Rica, pressure is being exerted to reduce consumption of palm oil. These events can only lead to increased costs, a decreased quality of the food supply, and subsequent hunger in areas of the developing world where there is a serious shortage of calories and fat.
1. Dupont J, White PJ, Feldman EB. Saturated and hydrogenated fats in food in relation to health. J Am Coll Nutr 1991; 10:57792.
2. USDA Science and Education Administration. Composition of foods, fats and oils. Agriculture Handbook no. 8-4. Washington, DC: US Government Printing Oftice,1979.
3. Hegsted DM, McGandy RB, Myers ML, Stare FJ. Quantitative effects of dietary fat on serum cholesterol in man. Am J Clin Nutr 1965;17:281-95.
4. Hayes KC, Pronczuk A, Lindsay S, Diersen-Schade D. Dietary saturated fatty acids (12:0,14:0,16:0) differ in their effects on plasma cholesterol and lipoproteins in nonhuman primates. Am J Clin Nutr 1991 ;53:491 -99.
5. Lindsey S, Benattar J, Pronczuc A. Hayes KC. Dietary palmitic acid (16:0) enhances high density lipoprotein cholesterol and low density lipoprotein receptor mRNA abundance in hamsters. Proc Soc Exp Biol Med 1990: 195:261 -69.
6. Rudel LL, Haines JL, Sawyer JK. Effects on plasma lipoproteins of monounsaturated, saturated, and polyunsaturated fatty acids in the diet of African green monkeys. J Lipid Res 1990;31:1873-82.
7. Kesteloot H, Oviasu VO, Obasohan AO, Olamu A, Cobbaert C, Lissens W. Serum lipid and apolipoprotein levels in a Nigerian population sample. Atherosclerosis 1989;78:33-38.
8. Park YK, Yetley EA. Trend changes in use and current intake of tropical oils in the United States. Am J Clin Nutr 1990;51:738-48.