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Safety evaluation of hydrogenated oils
Fd Chem. Toxic. Vol. 28, No. 1I, pp. 755-757, 1990
0278-6915/90 $3.00 + 0.00 Pergamon Press plc
Printed in Great Britain
SAFETY EVALUATION OF HYDROGENATED OILS P. M. VERSCHUREN and J. L. ZEVENBERGEY Unilever Research Laboratorium, Olivier van Noortlaan 120, 3133 AT, Vlaardingen, The Netherlands
Introduction
Processed foods have become an important part of the diet in industrialized countries. Advances in technology have brought about significant changes in the production methods in the food industry and have led to an improvement in texture, colour, shelflife and taste of conventional food products and to the development of novel foods. The safety evaluation of food components has advanced at a rapid pace and is no longer limited to the toxicology of additives and contaminants. The evaluation of the safety of macronutrients is becoming an area of increasing scrutiny, in order to ensure that food processing does not lead to unacceptable changes in the nutritional properties and safety of food products. The evaluation of the biological effects of processed foods distinguishes itself from the safety evaluation of food additives in several aspects. A major problem with respect to toxicological testing of foods in general is that toxicological evaluation of every chemical compound isolated is not tenable. The sensitivity of modern analytical techniques is such that suspect chemicals will be found in any food tested, whether it is as natural as a mother's milk, as simple as water, or as abused as a burned dinner! A more pragmatic approach is therefore required. This comprises the testing of processed foods as prepared or handled under normal factory conditions. In order to illustrate the specific problems that may arise with respect to macronutrient research this paper will focus on fats.
Problems in the safety assessment of macronutrients
Fat is a high energy component of the diet. By simply adding different levels of fat to a ready-made commercial diet, the caloric density will increase. Consequently, the energy balance will be distorted leading to a nutritional imbalance. This implies that in studying the safety aspects of processed fats in animal trials it is imperative to investigate the test material as a part of a well balanced diet. The use of purified diets carefully checked for palatability and nutritional adequacy is a necessity. In food additive toxicology procedures the socalled acceptable daily intake is obtained by dividing the no-observed-effect level by a safety factor (in general 100). However, this classical approach cannot be applied to macronutrients. When investigating a macronutrient such as fat, it is practically impossible to overdose animals with this energy-rich nutrient without inducing experimental artefacts due to diet-
ary imbalance. So a large safety factor between the level that should not induce any adverse effect in a laboratory animal and its ADI cannot be applied. In the edible-fat industry the hardening of vegetable oils by hydrogenation is a widely applied process. The main aim of this process is to shift the melting range of edible oils to higher temperatures to obtain solid fats for the production of margarines and shortenings. During the hydrogenation process cisunsaturated fatty acids are converted into saturated fatty acids and trans-unsaturated fatty acids. These are mainly monoenes, isomers of oleic acid. In addition, small amounts of geometric and/or positional isomers of dienoic acids are formed, primarily cis, trans- and some trans,trans-linoleic acid isomers (Dutton, 1979). In order to establish the specific effects of transfatty acids, proper comparisons must be made; comparison of a hydrogenated oil with the corresponding non-hydrogenated oil, or of fat mixtures differing in their saturated and polyunsaturated fattyacid content will not yield meaningful results. Another form of improper comparison involves the use of extreme fat mixtures, for instance those containing insufficient essential fatty acids or large quantities of fatty acids, for example trans,trans-linoleic acid, which are not present in appreciable amounts in conventional products. The above-mentioned points highlight the pitfalls, shortcomings and impracticabilities of the classical toxicological approaches to safety assessment of macronutrients such as hydrogenated fats. The traditional methods have to be replaced by proper experiments designed by a multidisciplinary research group (comprising analytical chemists, nutritionists, physiologists, biochemists, toxicologists and pathologists) using balanced diets and criteria selected for their high sensitivity to act as indicators of possible long-term consequences. Toxicity of trans-fatty acids
The comprehensive literature on trans-fatty acids indicates that these compounds do not give rise to direct toxic effects. Nevertheless, concern has been expressed about the safety of the hydrogenation process. It has been suggested that trans-fatty acids may interfere with the metabolism of essential fatty acids (e.g. by decreasing the synthesis of certain prostaglandins) thereby possibly increasing the requirement for essential fatty acids. Like ordinary fatty acids, trans-fatty acids are incorporated into tissue lipids, which could have consequences for the functioning of cells and cell organelles. Moreover, it 755
756
P.M. VERSCHURENand J. L. ZEVENBERGEN
has been pointed out that by inducing peroxisome formation trans-fatty acids could play a role in carcinogenesis. Extensive long-term studies meeting the previously mentioned criteria, with mice, rats and rabbits fed partially hydrogenated fats, did not show adverse effects of trans-fatty acids on growth, longevity, reproductive performance or histopathology of many organs (Alfin-Slater et al., 1957 and 1976; Nolen et al.+ 1967; Vles and Gottenbos, 1972a,b). Recent studies with mice and rats have shown no difference in tumour promotion between trans-fatty acids and cis-monounsaturated or saturated fatty acids (Brown, 1981; Erickson et al., 1984; Selenkas et al., 1984). Trans-fatty acids appeared to be no more atherogenic than saturated fatty acids (Royce et al., 1984; Vles et al., 1977). As with saturated fatty acids, the atherogenic effect of trans-fatty acids was reduced by increasing the amount of linoleic acid in the diet (Vies et al., 1977). Like other fatty acids trans-fatty acids are incorporated into the biomembranes of animal and human tissues, but the mere presence of trans-fatty acids in the biomembrane does not necessarily imply that the function of that membrane will be disturbed or even changed. If, for example, the fatty acid composition of the mitochondrial membrane is altered by feeding trans-fatty acids (Blomstrand and Svensson, 1983; Hoy and Holmer, 1979), the oxidative phosphorylation of m i t o c h o n d r i a - - w h i c h is strongly dependent on a high structural integrity of the inner mitochondrial membrane is not affected (Blomstrand and Svensson, 1983; Royce and Holmes, 1984). Recently, we performed additional rat studies in order to define the minimum amount of linoleic acid required to prevent undesirable effects of trans-fatty acids and to compare trans-fatty acids with cismonounsaturated and saturated fatty acids. Feeding rats high amounts of trans-fatty acids with increasing amounts of linoleic acid (1 17%) revealed that no specific effects were to be expected with 5% (or more) linoleic acid in the fat fraction of the diet (J. L. Zevenbergen and P. M. Verschuren, unpublished data, 1988). The subsequent comparison study of trans-fatty acids, saturated fatty acids and cismonounsaturated fatty acids showed no significant differences between trans-fatty acid groups and the other groups with respect to the eicosanoid synthesis of blood platelets and pieces of aorta (Zevenbergen and Haddeman, 1989). Despite significant changes in the fatty acid composition of the mitochondria, we also found that their function (oxidative phosphorylation) was not changed by feeding trans-fatty acids (Zevenbergen et al., 1988). It is now generally accepted that trans-fatty acids do not induce adverse effects provided sufficient linoleic acid is present in the diet (Beare-Rogers, 1983; Emken, 1984: Gottenbos, 1983). In view of the level of linoleic acid in the Western diet (on average more than 5% of the fat) and the trans-fatty acid content in the diet (less than 10%), it is evident that trans-fatty acids do not present a health problem, The recent review of the ad hoc panel of the Federation of American Societies for Experimental Biology (1985) confirms this conclusion in its statement that, +'The available scientific information suggests little
reason for concern with the safety of trans-fatty acids both at their present and expected levels of consumption and at the present and expected levels of consumption of linoleic acid". Most of the indications of adverse effects of trans-fatty acids came from experiments aimed at establishing the potential effect of trans-fatty acids, in which extreme dietary compositions were used that never occur in practice. In macronutrient research in general, and in fat research in particular. it must be realized that extreme dietary compositions restrict the choice of fatty acids available to the organism and limit the possibilities to carry out normal metabolic processes. To evaluate the nutritional, physiological and biochemical effects of trans-fatty acids, physiologically similar components, namely saturated or cis-monounsaturated fatty acids, should be used for comparison. Moreover, the experimental diets should be nutritionally adequate.
REFERENCES
Alfin-Slater R+ B., Aflergood L. and Whitten T. (1976) Nutritional value of trans fatty acids. J. Am. Oil Chem. Soc. 53, 458A. Alfin-Slater R. B., Wells A. F.+ Aflergood L. and Deuel H. J. (1957) Nutritive value and safety of hydrogenated vegetable fats as evaluated by longterm feeding experiments with rats. J. Nutr. 63, 241-261. Beare-Rogers J. L. (1983) Trans- and positional isomers of common fatty acids. In Adrances in Nutritional Research. Edited by H. Draper. Vol. 5. pp. 171 200. Plenum, New York. Blomstrand R. and Svensson L. (1983) The effects of partially hydrogenated marine oils on the mitochondrial function and membrane phospholipid fatty acids in rat heart. Lipids 18, 151 170. Brown R. R. (1981) Effects of dietary fats on incidence of spontaneous and induced cancer in mice. Cancer Res. 41, 3741 3742. Dutton H. J. (1979) Hydrogenation of fats and its significance. In Geometric and Positional Fatty Acid Isomers. Edited by E. A. Emken and H. J. Dutton. pp. 1+16. American Oil Chemists Society, Champaign. IL. Emken E. A. (1984) Nutrition and biochemistry of trans and positional fatty acid isomers in hydrogenated oils. Ann. Rev. Nutr. 4, 339 376. Erickson K. L., Schanger D. S., Adams D. A.. Fregeau D. R. and Stern J. S. (1984) Influence of dietary fatty acid concentration and geometric configuration on murine mammary tumorigenesis and experimental metastasis. J. Nutr. 114, 1834 1842. FASEB (1985) Report of the Ad-hoc Committee of the Federation of American Societies for Experimental Biology. Health Aspects of Dietary Trans Fatty Acids. Edited by F. R. Senti, FASEB, Washington, DC. Gottenbos J. J. (1983) Biological effects of trans fatty acids. In Dicta O, Fats and Health. Edited by E. G. Perkins and W. J. Visek. pp. 375 390. American Oil Chemists" Society, Champaign, IL. Hoy C. E. and Holmer G. (1979) Incorporation of cis- and trans-octadecenoic acids into the membranes of rat liver mitochondria. Lipids 4, 717 733. Nolen G. A., Alexander J. G+ and Artman N. R. (1967) Long-term rat feeding study with used frying fats. J. Nutr. 93, 337-348.
Safety evaluation of hydrogenated oils Royce S. M. and Holmes R. P. (1984) The saturation and isomeration of dietary fatty acids and the respiratory properties of rat heart mitochondria. Biochem. biophys. Acta 792, 371-375. Royce S. M., Holmes R. P., Takagi T. and Kummerov F. A. (1984) The influence of dietary isomeric and saturated fatty acids on atherosclerosis and eicosanoid synthesis in swine. Am. J. clin. Nutr. 39, 215 222. Selenkas S. L., lp M. M. and Ip C. (1984) Similarity between trans fat and saturated fat in the modification of rat mammary carcinogenesis. Cancer Res. 44, 1321-1326. Vies R. O. and Gottenbos J. J. (1972a) Long term effects of feeding butter fat, coconut oil and hydrogenated and non-hydrogenated soyabean oils 1. Eighteen-month experiment in mice. Voeding 33, 428-433.
757
Vies R. O. and Gottenbos J. J. (1972b) Long-term effects of feeding butter fat, coconut oil and hydrogenated and non-hydrogenated soyabean oils 2. Life span experiments in rats. Voeding 33, 455-465. Vles R. O., Gottenbos J. J. and van Pijpen P. L. (1977) Aspects nutritionels des huiles de soya hydrogenees et leur acides gras insaturs isomeriques. Biblthca 'nutr. Dieta' 25, 186-196. Zevenbergen J. L. and Haddeman E. (1989) Lack of effects of trans fatty acids on eicosanoid biosynthesis with adequate intakes of linoleic acid. Lipids, 24. 555-563. Zevenbergen J. L., Houtsmuller U. M. T. and Gottenbos J. J. (1988) Linoleic acid requirements of rats fed trans fatty acids. Lipids 23, 178 186. Zevenbergen J. L. and Verschuren P. M. (1988) Linoleic acid requirement of rats fed trans fatty acids. A Nutritional study. J. Nutr. In press.
0278-6915/90 $3.00 + 0.00 Pergamon Press plc
Printed in Great Britain
SAFETY EVALUATION OF HYDROGENATED OILS P. M. VERSCHUREN and J. L. ZEVENBERGEY Unilever Research Laboratorium, Olivier van Noortlaan 120, 3133 AT, Vlaardingen, The Netherlands
Introduction
Processed foods have become an important part of the diet in industrialized countries. Advances in technology have brought about significant changes in the production methods in the food industry and have led to an improvement in texture, colour, shelflife and taste of conventional food products and to the development of novel foods. The safety evaluation of food components has advanced at a rapid pace and is no longer limited to the toxicology of additives and contaminants. The evaluation of the safety of macronutrients is becoming an area of increasing scrutiny, in order to ensure that food processing does not lead to unacceptable changes in the nutritional properties and safety of food products. The evaluation of the biological effects of processed foods distinguishes itself from the safety evaluation of food additives in several aspects. A major problem with respect to toxicological testing of foods in general is that toxicological evaluation of every chemical compound isolated is not tenable. The sensitivity of modern analytical techniques is such that suspect chemicals will be found in any food tested, whether it is as natural as a mother's milk, as simple as water, or as abused as a burned dinner! A more pragmatic approach is therefore required. This comprises the testing of processed foods as prepared or handled under normal factory conditions. In order to illustrate the specific problems that may arise with respect to macronutrient research this paper will focus on fats.
Problems in the safety assessment of macronutrients
Fat is a high energy component of the diet. By simply adding different levels of fat to a ready-made commercial diet, the caloric density will increase. Consequently, the energy balance will be distorted leading to a nutritional imbalance. This implies that in studying the safety aspects of processed fats in animal trials it is imperative to investigate the test material as a part of a well balanced diet. The use of purified diets carefully checked for palatability and nutritional adequacy is a necessity. In food additive toxicology procedures the socalled acceptable daily intake is obtained by dividing the no-observed-effect level by a safety factor (in general 100). However, this classical approach cannot be applied to macronutrients. When investigating a macronutrient such as fat, it is practically impossible to overdose animals with this energy-rich nutrient without inducing experimental artefacts due to diet-
ary imbalance. So a large safety factor between the level that should not induce any adverse effect in a laboratory animal and its ADI cannot be applied. In the edible-fat industry the hardening of vegetable oils by hydrogenation is a widely applied process. The main aim of this process is to shift the melting range of edible oils to higher temperatures to obtain solid fats for the production of margarines and shortenings. During the hydrogenation process cisunsaturated fatty acids are converted into saturated fatty acids and trans-unsaturated fatty acids. These are mainly monoenes, isomers of oleic acid. In addition, small amounts of geometric and/or positional isomers of dienoic acids are formed, primarily cis, trans- and some trans,trans-linoleic acid isomers (Dutton, 1979). In order to establish the specific effects of transfatty acids, proper comparisons must be made; comparison of a hydrogenated oil with the corresponding non-hydrogenated oil, or of fat mixtures differing in their saturated and polyunsaturated fattyacid content will not yield meaningful results. Another form of improper comparison involves the use of extreme fat mixtures, for instance those containing insufficient essential fatty acids or large quantities of fatty acids, for example trans,trans-linoleic acid, which are not present in appreciable amounts in conventional products. The above-mentioned points highlight the pitfalls, shortcomings and impracticabilities of the classical toxicological approaches to safety assessment of macronutrients such as hydrogenated fats. The traditional methods have to be replaced by proper experiments designed by a multidisciplinary research group (comprising analytical chemists, nutritionists, physiologists, biochemists, toxicologists and pathologists) using balanced diets and criteria selected for their high sensitivity to act as indicators of possible long-term consequences. Toxicity of trans-fatty acids
The comprehensive literature on trans-fatty acids indicates that these compounds do not give rise to direct toxic effects. Nevertheless, concern has been expressed about the safety of the hydrogenation process. It has been suggested that trans-fatty acids may interfere with the metabolism of essential fatty acids (e.g. by decreasing the synthesis of certain prostaglandins) thereby possibly increasing the requirement for essential fatty acids. Like ordinary fatty acids, trans-fatty acids are incorporated into tissue lipids, which could have consequences for the functioning of cells and cell organelles. Moreover, it 755
756
P.M. VERSCHURENand J. L. ZEVENBERGEN
has been pointed out that by inducing peroxisome formation trans-fatty acids could play a role in carcinogenesis. Extensive long-term studies meeting the previously mentioned criteria, with mice, rats and rabbits fed partially hydrogenated fats, did not show adverse effects of trans-fatty acids on growth, longevity, reproductive performance or histopathology of many organs (Alfin-Slater et al., 1957 and 1976; Nolen et al.+ 1967; Vles and Gottenbos, 1972a,b). Recent studies with mice and rats have shown no difference in tumour promotion between trans-fatty acids and cis-monounsaturated or saturated fatty acids (Brown, 1981; Erickson et al., 1984; Selenkas et al., 1984). Trans-fatty acids appeared to be no more atherogenic than saturated fatty acids (Royce et al., 1984; Vles et al., 1977). As with saturated fatty acids, the atherogenic effect of trans-fatty acids was reduced by increasing the amount of linoleic acid in the diet (Vies et al., 1977). Like other fatty acids trans-fatty acids are incorporated into the biomembranes of animal and human tissues, but the mere presence of trans-fatty acids in the biomembrane does not necessarily imply that the function of that membrane will be disturbed or even changed. If, for example, the fatty acid composition of the mitochondrial membrane is altered by feeding trans-fatty acids (Blomstrand and Svensson, 1983; Hoy and Holmer, 1979), the oxidative phosphorylation of m i t o c h o n d r i a - - w h i c h is strongly dependent on a high structural integrity of the inner mitochondrial membrane is not affected (Blomstrand and Svensson, 1983; Royce and Holmes, 1984). Recently, we performed additional rat studies in order to define the minimum amount of linoleic acid required to prevent undesirable effects of trans-fatty acids and to compare trans-fatty acids with cismonounsaturated and saturated fatty acids. Feeding rats high amounts of trans-fatty acids with increasing amounts of linoleic acid (1 17%) revealed that no specific effects were to be expected with 5% (or more) linoleic acid in the fat fraction of the diet (J. L. Zevenbergen and P. M. Verschuren, unpublished data, 1988). The subsequent comparison study of trans-fatty acids, saturated fatty acids and cismonounsaturated fatty acids showed no significant differences between trans-fatty acid groups and the other groups with respect to the eicosanoid synthesis of blood platelets and pieces of aorta (Zevenbergen and Haddeman, 1989). Despite significant changes in the fatty acid composition of the mitochondria, we also found that their function (oxidative phosphorylation) was not changed by feeding trans-fatty acids (Zevenbergen et al., 1988). It is now generally accepted that trans-fatty acids do not induce adverse effects provided sufficient linoleic acid is present in the diet (Beare-Rogers, 1983; Emken, 1984: Gottenbos, 1983). In view of the level of linoleic acid in the Western diet (on average more than 5% of the fat) and the trans-fatty acid content in the diet (less than 10%), it is evident that trans-fatty acids do not present a health problem, The recent review of the ad hoc panel of the Federation of American Societies for Experimental Biology (1985) confirms this conclusion in its statement that, +'The available scientific information suggests little
reason for concern with the safety of trans-fatty acids both at their present and expected levels of consumption and at the present and expected levels of consumption of linoleic acid". Most of the indications of adverse effects of trans-fatty acids came from experiments aimed at establishing the potential effect of trans-fatty acids, in which extreme dietary compositions were used that never occur in practice. In macronutrient research in general, and in fat research in particular. it must be realized that extreme dietary compositions restrict the choice of fatty acids available to the organism and limit the possibilities to carry out normal metabolic processes. To evaluate the nutritional, physiological and biochemical effects of trans-fatty acids, physiologically similar components, namely saturated or cis-monounsaturated fatty acids, should be used for comparison. Moreover, the experimental diets should be nutritionally adequate.
REFERENCES
Alfin-Slater R+ B., Aflergood L. and Whitten T. (1976) Nutritional value of trans fatty acids. J. Am. Oil Chem. Soc. 53, 458A. Alfin-Slater R. B., Wells A. F.+ Aflergood L. and Deuel H. J. (1957) Nutritive value and safety of hydrogenated vegetable fats as evaluated by longterm feeding experiments with rats. J. Nutr. 63, 241-261. Beare-Rogers J. L. (1983) Trans- and positional isomers of common fatty acids. In Adrances in Nutritional Research. Edited by H. Draper. Vol. 5. pp. 171 200. Plenum, New York. Blomstrand R. and Svensson L. (1983) The effects of partially hydrogenated marine oils on the mitochondrial function and membrane phospholipid fatty acids in rat heart. Lipids 18, 151 170. Brown R. R. (1981) Effects of dietary fats on incidence of spontaneous and induced cancer in mice. Cancer Res. 41, 3741 3742. Dutton H. J. (1979) Hydrogenation of fats and its significance. In Geometric and Positional Fatty Acid Isomers. Edited by E. A. Emken and H. J. Dutton. pp. 1+16. American Oil Chemists Society, Champaign. IL. Emken E. A. (1984) Nutrition and biochemistry of trans and positional fatty acid isomers in hydrogenated oils. Ann. Rev. Nutr. 4, 339 376. Erickson K. L., Schanger D. S., Adams D. A.. Fregeau D. R. and Stern J. S. (1984) Influence of dietary fatty acid concentration and geometric configuration on murine mammary tumorigenesis and experimental metastasis. J. Nutr. 114, 1834 1842. FASEB (1985) Report of the Ad-hoc Committee of the Federation of American Societies for Experimental Biology. Health Aspects of Dietary Trans Fatty Acids. Edited by F. R. Senti, FASEB, Washington, DC. Gottenbos J. J. (1983) Biological effects of trans fatty acids. In Dicta O, Fats and Health. Edited by E. G. Perkins and W. J. Visek. pp. 375 390. American Oil Chemists" Society, Champaign, IL. Hoy C. E. and Holmer G. (1979) Incorporation of cis- and trans-octadecenoic acids into the membranes of rat liver mitochondria. Lipids 4, 717 733. Nolen G. A., Alexander J. G+ and Artman N. R. (1967) Long-term rat feeding study with used frying fats. J. Nutr. 93, 337-348.
Safety evaluation of hydrogenated oils Royce S. M. and Holmes R. P. (1984) The saturation and isomeration of dietary fatty acids and the respiratory properties of rat heart mitochondria. Biochem. biophys. Acta 792, 371-375. Royce S. M., Holmes R. P., Takagi T. and Kummerov F. A. (1984) The influence of dietary isomeric and saturated fatty acids on atherosclerosis and eicosanoid synthesis in swine. Am. J. clin. Nutr. 39, 215 222. Selenkas S. L., lp M. M. and Ip C. (1984) Similarity between trans fat and saturated fat in the modification of rat mammary carcinogenesis. Cancer Res. 44, 1321-1326. Vies R. O. and Gottenbos J. J. (1972a) Long term effects of feeding butter fat, coconut oil and hydrogenated and non-hydrogenated soyabean oils 1. Eighteen-month experiment in mice. Voeding 33, 428-433.
757
Vies R. O. and Gottenbos J. J. (1972b) Long-term effects of feeding butter fat, coconut oil and hydrogenated and non-hydrogenated soyabean oils 2. Life span experiments in rats. Voeding 33, 455-465. Vles R. O., Gottenbos J. J. and van Pijpen P. L. (1977) Aspects nutritionels des huiles de soya hydrogenees et leur acides gras insaturs isomeriques. Biblthca 'nutr. Dieta' 25, 186-196. Zevenbergen J. L. and Haddeman E. (1989) Lack of effects of trans fatty acids on eicosanoid biosynthesis with adequate intakes of linoleic acid. Lipids, 24. 555-563. Zevenbergen J. L., Houtsmuller U. M. T. and Gottenbos J. J. (1988) Linoleic acid requirements of rats fed trans fatty acids. Lipids 23, 178 186. Zevenbergen J. L. and Verschuren P. M. (1988) Linoleic acid requirement of rats fed trans fatty acids. A Nutritional study. J. Nutr. In press.