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Nutritional Aspects of Cardiovascular Disease

Report of the Cardiovascular Review Group of the Committee of Medical Aspects of Food Policy number 46. Department of Health 1994, HMSO.

As of 2004, this report is still the most recent official report in the UK that gives advice and recommendations on trans fats. It is also frequently quoted by the food industry, often in misleading ways. Hence we present these extracts from the report.

Summary

S.2.4. Trans fatty acids (mainly from hydrogenated fat in margarines and shortenings and products made from them, eg biscuits, pastries; also from meat and dairy products). A number of recent studues, both experimental and epidemiological, indicate that trans fatty acids, particularly those from margarines and cooking fats, may have undesirable effects not only on plasma LDL and HDL cholesterol, but also on Lp(a) and CHD mortality (see 6.2.5). The average intake of of trans fatty acids, at present, is about 2 per cent of food energy, or about 5g per day. We recommend that, on average, trans fatty acids should provide no more than the current average of about 2% of dietary energy and that consideration should be given to ways of decreasing the amount present in the diet.

S.2.5. Total fat ... The present average proportion of food energy derived from total fat is about 40 per cent. We recommend a reduction in the average contribution of total fat to dietary energy in the population to about 35 per cent. We recommend more research is done into the diverse biological effects of dietary lipids.

Chapter 6. Diet and risk:

Summary. [...] Trans fatty acids, principally those from the artificial hydrogenation (hardening) of vegetable and animal fats, raise LDL cholesterol and plasma triglycerides, and lower HDL cholesterol. A positive relationship between trans fatty acid intake, particularly from hydrogenated fats, and risk of CHD has been reported. [...]

6.2.6. Trans fatty acids Hydrogenated fats are a major dietary source of trans and positional isomers of fatty acids (see 4.1.6). More recent 'polyunsaturated' margarines have lower contents of trans fatty acids than older hard margarines. A number of recent expert committees have reviewed the evidence on the biological effects of both kinds of isomeric fatty acid. [60, 234]

6.2.6.1. The metabolism of trans fatty acids has been recently reviewed by COMA [2], who concluded that trans fatty acids should not be regarded as equivalent either to their cis counterparts or to saturated fatty acids. More recent data on the effects of trans fatty acids on blood cholesterol have since been reported.

6.2.6.2. Investigations of the influence of trans fatty acids on blood cholesterol have shown both elevating and neutral effects, but there are problems in interpreting much of the data. In 1990 Mensink and Katan [235] published the results of a carefully conducted experiment on 34 women and 24 men in the Netherlands, comparing solid diets with differering contents of oleic (cis C18:1), elaidic (trans C18:1), and saturated (C12-C16) fatty acis. In comparison with oleic acid, C18:1 trans fatty acids were found to raise LDL cholesterol, although not by as much as saturated fatty acids, and to decrease HDL cholesterol. The LDL/HDL cholesterol ratio was higher on the trans fatty acid diet than on the saturated fatty acid diet. The content of trans fatty acids in the experimental diet was relatively high (about 11% of dietary energy, compared to average intakes in the UK of about 2% of energy, although substantially higher intakes might occur in some individuals [60]). A second study using 7% of trans fatty acids found a similar but smaller effect suggesting a linear dose-response relationship [236]. A similar study in Australia, using 7% of energy as elaidic acid, found that elaidic acid raised plasma LDL levels to a similar extent as saturated fatty acids, with no change in HDL levels [237]. A study, conducted by the US Department of Agriculture, substituting either 3% or 6% of energy from oleic acid with trans fatty acids found a dose response rise in plasma LDL cholesterol levels, and a decrease in plasma HDL cholesterol levels at the higher dose of trans fatty acids [238].

6.2.6.3. Findings consistent with those of Mensink and Katan have recently been reported in three epidemiological studies. Troisi et al [239] in a cross sectional study of 748 men found a direct relationship between intake of trans fatty acids and blood total and LDL cholesterol, and an inverse relationship with HDL cholesterol. Willet et al [240] reported findings from the Nurses Health Study, a prospective study involving more than 85,000 women, showing that intake of trans fatty acids was significantly and independently associated with incidence of CHD. The association was only seen for for trans fatty isomers from hydrogenated vegetable oils. The mainly different trans isomers from ruminant fats did not show such an association. A case-control study in 239 people suffering an acute myocardial infarction found that after adjustment for age, sex and energy intake, intake of trans fatty acids was directly related to risk of myocardial infarction [241]. Those with the highest intake of trans fatty acids had twice the risk of myocardial infarction as those with the lowest intakes after adjusting for other cardiovascular risk factors. As with the Nurses Health Study, the association was only seen for trans isomers from partially hydrogenated vegetable oils.

6.2.6.4. Two studies have recently been published showing that trans fatty acids at similar levels to those tested above raise Lp(a) levels. [237, 242]. Mensink et al measured the changes in Lp(a) in three previous experiments comparing 11% and 8% trans fatty acids with saturated fatty acids, monounsaturated fatty acids and linoleic acid. They found that Lp(a) levels were significantly higher on the trans fatty acid diets in comparison with the other diets. They suggested that their previous report that the replacement of the habitual fat by palm oil lowered Lp(a) in normolipidaemic men [243] might have been the result of the displacement of 50% of the trans fatty acids by palm oil. Nestel et al found a significant increase in Lp(a) n a 7% elaidic acid diet compared to a saturated fatty acid diet in mildly hypercholesterolaemic men. A third study, using hydrogenated corn oil, found no effect on Lp(a) levels.

6.2.6.5. There are suggestions that trans fatty acids can compete with essential fatty acids, especially at low intakes of the latter, for delta-6 and delta-5 desaturases, the enzymes responsible for converting linoleic acid (C18:2 n-6) and alpha-linolenic acid (C18:3 n-3) to their longer chain derivatives, respectively arachidonic acid (C20:4 n-6) and eicosapentaenoic acid (C20:5 n-3) [245]. Recent research suggests that this might occur even when essential fatty acid intake is not marginal, although this needs to be confirmed [245].

6.2.10. Recommendations We recommend that the average contribution of saturated fatty acids to dietary energy be reduced to no more than about 10 per cent. Monounsaturates (oleic acid) may partly offset this reduction so long as total fat intake does not exceed about 35 per cent of energy ... Trans fatty acid intake in the population should not increase beyond the current estimated average of 5 g/day or 2 of cent of dietary energy and consideration should be given to ways of decreasing the amount present in the diet. [...]

References

2 to be supplied.
60 British Nutrition Foundation. Task Force on Trans Fatty Acids. Trans fatty acids: report of the British Nutrition Foundation's Task Force. London: British Nutrition Foundation, 1987.
234 Federation of American Societies for Experimental Biology. LIfe Sciences Research Office. Health aspects of dietary 'trans' fatty acids. Bethseda MD: Federation of American Societies for Experimental Biology, 1985. Report No: FDA/CFSAN-86/1.
235 Mensink RP, Katan MB. Effect of dietary trans fatty acids on high-denisty and low-density lipoprotein cholesterol levels in healthy subjects. New England Journal of Medicine 1990; 323: 439-45.
237 Nestel P, Noakes M, Belling B, et al. Plasma lipoprotein lipid and Lp(a) changes with subsitution of elaidic acid for oleic acid in the diet. Journal of Lipid Research 1992; 33: 1029-36.
238 Judd JT, Clevidence BA, Muesing RA, Wittes J, Sunkin ME, Podczasy JJ. Dietary trans fatty acids: effects on plasma lipids and lipoproteins of healthy men and women. American Journal of Clinical Nutrition; 59: 861-868.
239 Troisi R, Willett WC, Weiss ST. Trans-fatty acid intake in relation to serum lipid concentratins in adult men. American Journal of Clinical Nutrition; 56: 1018-1024.
240 Willett WC, Stampfer MJ, Manson JE, et al. Intake of trans fatty acids and risk of coronoary heart disease among women. Lancet 1993; 341: 581-5.
241 Ascherio A, Hennekens CH, Buring JE, Master C, Stampfer MJ, Willett WC. Trans fatty acids intake and risk of myocardial infarction. Circulation 1994; 89: 94-101.
242 Mensink RP, Zock PL, Katan MB, Hornstra G. Effect of dietary cis and trans fatty acids on serum lipoprotein (a) levels in humans. Journal of Lipid Research 1992; 33: 1493-501.
243 Hornstra G, van Houwelingen AC, Kester AD, Sundram K. A palm-oil enriched diet lowers serum lipoprotein(a) in normocholesterolemic volunteers. Artheroscelerosis 1991: 90: 91-3.
245 Wahle KWJ, James WPT. Isomeric fatty acids and human health. European Journal of Clinical Nutrition 1993; 47: 828-39.
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