Trans fatty acids are produced when oils and fats containing unsaturated fatty acids are hydrogenated in the presence of a catalyst.



Trans fatty acids are produced when oils and fats containing unsaturated fatty acids are hydrogenated in the presence of a catalyst. Hydrogenation primarily increases the melting range of the unsaturated fats and thereby enables their incorporation into many solid fat formulations. When an unsaturated fat or oil is fully hydrogenated, all the unsaturated fatty acids are converted into their saturated analogues. Since the unsaturation in most vegetable oils is largely in the 18-carbon fatty acids, namely, oleic (18:1 n-9), linoleic (18:2 n-6) and linoleic (18:3 n-3), full hydrogenation of such oils would result in a stearic acid (18:0), high melting block of fat. Partial hydrogenation, usually in the presence of nickel catalysts, results in the formation of trans fatty acids that are the geometrical isomers of the unsaturated fatty acids, containing at least one double bond in the trans configuration.

This trans double bond configuration impacts the physical properties of the fatty acid with a potential for reducing the fluidity of the fatty acid thereby increasing its melting point. Thus, partial hydrogenation of liquid oils has been the tool of choice to enable their use in solid fats, especially margarine, formulations. Partial hydrogenation actually results in both cis and trans fatty acids anywhere between carbon 4 and carbon 16 of the fatty acid molecule with elaidic acid (9trans 18:1) being a major isomer and smaller amounts of numerous other trans isomers occurring concurrently. Upwards of 20 different cis and trans geometrical isomers have been recorded following partial hydrogenation of vegetable oils. Small amounts of trans fatty acids occur naturally in dairy fat (butter) and meat as a result of bio-hydrogenation in the fore stomach of ruminants.


*Malaysian Palm Oil Board, P .O. Box 10620, 50720 Kuala Lumpur, Malaysia.


Trans fatty acids are present in foods containing traditional stick margarine, bakery and frying fats, vegetable shortenings and vanaspati that have been subjected to hydrogenation. They have now become a universal food culture and are readily reflected in bakery products, fried foods, and breakfast margarine and, to a smaller extent, in dairy and meat products. Estimates of trans consumption are very varied and this has been hampered by a lack of an accurate database to reflect their contents in common foods. Indeed, even in the United States and Europe, this is a problem since trans fatty acid intake is still not featured in the national surveys of the United Sates and European community. Current trans consumption in the United States is estimated at about 2.6-3.0 energy percent whereas in some Middle Eastern and South Asian populations it may be as high as 7 energy percent.


Since their introduction into the human diet and until the early 1990s, partially hydrogenated fats containing trans fatty acids were advocated as the preferred fatty acid base for solid fats, especially margarines. They were initially designed to replace butterfat and with advancements in our knowledge about the adverse impacts of saturated fatty acids on cardiovascular disease (CVD) risk, trans fatty acids were made prominent as a safe alternative. Similar to other common fatty acids, trans fatty acids are efficiently absorbed in humans and completely catabolized to carbon dioxide and water. Variations in their geometrical configurations (relative to their cis fatty acids), melting behaviour and position of double bonds have no measurable effect on absorption efficiency. They are also incorporated into human adipose tissue and other organs just like cis fatty acids.

Current reflections on the string of events, largely advocated by powerful lobbies of the liquid vegetable oils producers, magnify the masking of important regulatory tools that were overlooked in favour of the use of partially hydrogenated fats by the food industry. Indeed had trans fatty acids being subjected to the same level of safety scrutiny as other food components, their adverse effects would have been spotted many decades ago. Yet after almost 50 years of a prescribed safe-use standard, trans fatty acids have been trust to the forefront by a series of studies that deliberately and surgically dissected their effects on blood cholesterol, lipoprotein metabolism and enhanced risk for cardiovascular disease.


Effects on Lipoprotein Cholesterol Concentration

After almost 50 years of little concern about the increased consumption trends of hydrogenated fats at the expense of saturated fatty acids, the study of Mensink and Katan (1990) suggested that trans increased total and low-density lipoprotein cholesterol (LDL-C) and decreased the beneficial high-density lipoprotein cholesterol (HDL-C) resulting in a less desirable total/HDL-C ratio. Nearly a dozen other studies quickly fortified this finding, almost all reflecting increases in the atherogenic LDL component and decreases in the beneficial HDL-component following the consumption of a trans enriched diet (Institute of Medicine, 2002). Invariably it was clearly established that trans fatty acids are worse than the saturated fatty acids they were designed to replace in the first instance. In this context, two palm oil studies (Sundram et al., 1997; Wood et al.,1993) stand out in this important groundbreaking cluster of studies and continue to be quoted by most expert panels as the standards of comparison that lead to the conclusion that trans constitute an increased and greater risk for cardiovascular risk than saturated fatty acids.

Effects on Lipoprotein Lp(a) Concentration

The lipoprotein (a) or Lp(a) concentration in human plasma when increased is considered an independent risk factor for CVD. The Lp(a) is mostly under genetic control and normally the diet has little influence on this risk predictor. However, the Lp(a) concentration has been reported to be increased after the consumption of diets enriched in hydrogenated fats containing trans fatty acids. The magnitude of the increase in Lp(a) associated with trans fatty acids is of concern especially in populations consuming high levels of trans fatty acids and in individuals with initially high concentrations of Lp(a). Of interest are several observations that have recorded decreases in Lp(a) following a saturated fat diet. Indeed, one of the earliest observations that detailed dietary modulation of Lp(a) was the Dutch palm oil study of Sundram et al. (1992). This demonstrated that maximal replacement of the regular fat content in the Dutch diet with palm oil resulted in significantly reduced Lp(a) concentrations accompanied by increases in the beneficial HDL-C. Sundram et al. (1997) subsequently demonstrated that when palm oil replaced a trans enriched diet, Lp(a) was significantly reduced by the palm oil diet, even in a low fat environment.

Epidemiological Evidence

The Harvard researchers led by Willett (1993) spearheaded studies elucidating the effects of trans fatty acids using epidemiological data from the Nurses Health Study consisting of 85 095 women. They examined the association between trans fatty acids and incidence of non-fatal myocardial infarction or death from coronary heart disease (CHD) in these women followed for eight years. A positive and significant association between trans and CHD was apparent. Foods that were major sources of trans including margarine and cookies also revealed a positive correlation. A follow-up study in 239 patients (Ascherio et al.,1994) also established a positive association between trans containing margarines and myocardial infarction. Trans intake was associated with increased total and LDL-cholesterol and negatively related to HDL-cholesterol in men suffering a myocardial infarction. Relative risk for CVD was increased by 27% as a result of trans consumption. These studies clearly established an association of trans fatty acid consumption with increased incidence and death from CVD and it was estimated that almost 80 000 deaths in the United States alone are associated with continued consumption of foods rich in trans fatty acids.


Recent studies have implicated trans fatty acids not only with coronary heart disease but also with increased risk and incidence of diabetes. Dietary fat intake was evaluated for CHD risk (Hu et al., 1997) and type II diabetes in women. A 2% increase in trans fatty acid consumption relative to carbohydrate intake resulted in a relative risk score of 1.93 for CHD and 1.39 for type II diabetes. In comparison, the score for saturated fatty acids was significantly lower: 1.17 for CHD and 0.97 for type II diabetes. These findings served to highlight additional concerns about the safety of trans fatty acids in humans.

Based on these findings and a complete review of all available published literature relating to trans fatty acids, the Institute of Medicine (IOM) of the National Academies (of Sciences, Engineering, Medicine and Research Council), USA declared that there are no data available to indicate a health benefit from consuming trans fatty acids. Therefore an Adequate Intake, Estimated Average Requirement, and Recommended Dietary Allowance are not established for trans fatty acids. There is a positive linear trend between trans fatty acid intake and total and LDL-C concentration and therefore increased risk of