Trans fatty acids in the Nordic countries

Abstract

Trans fatty acids (TFA) comprise a variety of positional isomers, mainly with 18 carbon atoms and one double bond (C18:1). They are found in foods of ruminant animal origin and in partially hydrogenated vegetable oils. The isomeric composition of TFA in animal and vegetable foods differs, but no definite differences have been documented between the metabolic and health effects of the different isomers. In the Nordic countries the intake of TFA has declined during the past 10–15 years, mainly through reduced use of partially hydrogenated vegetable oils. TFA are mainly found in foods that contain far higher amounts of saturated fatty acids (SFA). The proportion of SFA plus TFA should be kept to one-third of total dietary fatty acids. The problem of excessive consumption of these unfavourable fatty acids should be managed with food-based dietary guidelines in agreement with the Nordic Nutrition Recommendations.

• food-based dietary guidelines
• nutrition recommendations
• ruminant fat
• trans isomers
• vegetable fat

Introduction

Isomeric trans fatty acids (TFA) are found in foods that contain ruminant animal fats or vegetable oils that have been partially hydrogenated for technological purposes. In both sources the quantitatively most important class of TFA is the cluster of isomers containing 18 carbon atoms and one double bond (C18:1). The position of the trans double bond varies between the Δ4 [CE1]and Δ16 carbon atoms of the fatty acid molecule, and the Δ9–11 isomers are the most common ones 1. Trans-vaccenic acid (t-Δ11–18:1) comprises about 30–50% of the trans C18:1 isomers of ruminant animal fats, whereas in industrially hydrogenated fats elaidic acid (t-Δ9–C18:1) typically comprises 20–30% and t-Δ10–C18:1 and t-Δ11–C18:1 each contribute 10–20% of the C18:1 isomers 2.

Effects of different trans fatty acids

In Dutch and Finnish studies that showed the low-density lipoprotein (LDL)-cholesterol-increasing and high-density lipoprotein (HDL)-cholesterol-decreasing effects of high doses of TFA, the TFA were produced by partial hydrogenation of high-oleic acid sunflower oil 3–5345. The product that contained high proportions of the Δ6–9 isomers has not been used in commercially available fats. Partially hydrogenated fish oils that contain high amounts of Δ9 elaidic acid and in addition long-chain C20–22 trans isomers showed particularly strong effects on serum lipoproteins in a Norwegian study 6, whereas partially hydrogenated soybean oil with preponderance of the Δ10 isomer showed weak and non-significant effects on HDL-cholesterol in some studies 67. The Δ11 trans-vaccenic acid is to some extent desaturated in the human organism to conjugated linoleic acid (CLA) by Δ9 desaturase 8, but the health effects of this remain unknown. The effects on serum lipoproteins of trans-vaccenic acid have not been studied separately. Therefore, there may be some differences between the effects of different trans isomers, and additional studies on trans-vaccenic acid are needed 9. There was no significant difference in the effects of TFA of ruminant and vegetable origin on the risk of coronary heart disease (CHD) in the epidemiological studies when the intake levels were taken into account 10. Thus, on the basis of available evidence, all trans monoene fatty acids should be considered similar in their metabolic and health effects.

During partial hydrogenation TFA with more than one double bond are formed in small quantities. Such fatty acids may also be formed in non-hydrogenated vegetable oils due to heating of the oil during deodorization if special precautions are not taken 11. Even small amounts of these isomers have measurable unfavourable effects on blood lipids and lipoproteins with an increase in total cholesterol and the LDL-cholesterol:HDL-cholesterol ratio 12. Recently an observational study showed that high levels of trans-18:2 in red blood cell membranes, but not trans-18:1, were associated with increased risk of sudden cardiac death 13. It may therefore be prudent to pay more attention to this class of trans isomers.

Trans fatty acids in foods and dietary intake

Since the undesirable effects on lipoproteins of TFA were confirmed in 1990 3, attempts were started in Europe to reduce TFA in processed foods. Improved technology allowed the production of soft margarines containing only small amounts of TFA or without TFA. In the European TRANSFAIR study conducted in 1995–1996 it was found that low-trans margarines had been produced generally without increasing the proportions of saturated fatty acids (SFA) in the products 14. The new margarines that were available in all 14 participating countries soon became market leaders. The tendency appears to be that since removal of TFA, palmitic acid has become a dominating SFA in margarines 15. Considering the potent hypercholesterolaemic effect of palmitic acid a better alternative would be to replace at least part of the TFA with stearic acid.

In the TRANSFAIR study high amounts of TFA were found in certain industrial fats and processed foods such as potato chips, fatty pastries, biscuits, wafers and soup powders. The average contribution to total fat intake by TFA ranged from 0.5% of the energy intake (E%) in some Mediterranean countries to 2.1 E% in Iceland 16, which corresponds to about 1.5 and 7 g per day, respectively, at an energy intake of around 12 MJ/d. During the past 10 years the amounts of TFA derived from partially hydrogenated vegetable oils have been reduced in processed foods in the Nordic countries, but systematic studies of representative food samples have not been repeated since the TRANSFAIR study. In Norway the average intake of TFA was about 4 E% in 1958 17 but it had declined to 1.5 E% already in 1996. During the past 10 years the average intakes of TFA have been reduced further to 0.6 E% in Norway 18 and from 0.8 to 0.5 E% in Finland 19, apparently by reduced consumption of partially hydrogenated vegetable fats. In Sweden recent data show an average TFA intake of 0.9 E% among children, of which about half originates from ruminant fat and half presumably from partially hydrogenated vegetable fats 20.

The desired texture in Danish pastries, croissants and wafers, and the stability of fats used for biscuits or for repeated deep-frying are not achieved with unsaturated vegetable oils. Therefore, when partially hydrogenated vegetable fats are replaced in processed foods, fats such as coconut oil and other palm kernel oils containing high amounts of SFA and low in polyunsaturated fatty acids (PUFA) are commonly used. The present tendency to reduce TFA in industrial fats may lead to products that are higher in SFA and contain less unsaturated fatty acids than the previously available products. In Finland sweet biscuits that had been marketed after the year 2000 were found to contain no TFA, but most brands were high in SFA and low in cis-unsaturates, indicating the use of coconut oil. Similar trends have been observed for foods such as sweet bakery products on the Swedish market 21.

In a recent study a genetically modified (GM) plant oil that contained relatively small proportions of both SFA and PUFA had favourable effects on serum lipoproteins compared with partially hydrogenated vegetable oil 22. Novel GM oils may offer advantages for food production in the future, if their use becomes accepted in Europe.

Dietary guidelines

In the food-based dietary guidelines people will be advised to limit their consumption of high-fat processed foods, because their fatty acid composition is generally unfavourable irrespective of their TFA content. The fatty acid composition of dairy products and beef remain unchanged, but the TFA intake from processed foods is declining. In the Nordic countries, possibly with the exception of Iceland, the present average intake of TFA is between 0.5 and 1.0 E%, corresponding to about 1.5–3 g per day, and today the major part is derived from ruminant animal fats.

TFA are mainly found in foods that are also the main sources of SFA. TFA are a minor dietary component, but the foods that contain these fatty acids affect the balance between the favourable (cis-MUFA plus cis-PUFA) and unfavourable (SFA plus TFA) fats in the diet. According to the Nordic Nutrition Recommendations for 2004, the intake of MUFA plus PUFA should account for two-thirds and that of SFA plus TFA for a maximum of one-third (∼10 E%) of the total dietary fat intake 23. Based on epidemiological cohort studies, Oomen et al. 24 estimated that a reduction in TFA intake by 2 E% would reduce the risk of CHD by 25%. The effect that could be achieved in the Nordic countries would be about one-tenth of this. The recommended goal of 10 E% provided by dietary SFA plus TFA would require a reduction by one-third in the intakes of these fatty acids 23. Reduction in the consumption of SFA by 5 E% could reduce the risk of CHD by about 30%, assuming that SFA are replaced partly by MUFA and PUFA, and partly by carbohydrates 25. A corresponding decrease by 0.2–0.3 E% in TFA intake would have a small additional effect (∼3%) on the risk of CHD.

In the Nordic countries self-regulation by industry has resulted in markedly reduced intakes of TFA from partially hydrogenated vegetable oils. The problem of excessive consumption of the unfavourable fatty acids (SFA and TFA) should be managed by food-based dietary guidelines in agreement with the Nordic Nutrition Recommendations.