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Human lipid intake contains various amounts of trans fatty acids. Refined vegetable and frying oils, rich in linoleic acid and/or alpha-linolenic acid, are the main dietary sources of trans-18:2 and trans-18:3 fatty acids. The aim of the present study was to compare the oxidation of linoleic acid, alpha-linolenic acid, and their major trans isomers in human volunteers. For that purpose, TG, each containing two molecules of [1-(13)C]linoleic acid, alpha-[1-(13)C]linolenic acid, [1-(13)C]-9cis,12trans-18:2, or [1-(13)C]-9cis,12cis,15trans-18:3, were synthesized. Eight healthy young men ingested labeled TG mixed with 30 g of olive oil. Total CO(2) production and (13)CO(2) excretion were determined over 48 h. The pattern of oxidation was similar for the four fatty acids, with a peak at 8 h and a return to baseline at 24 h. Cumulative oxidation over 8 h of linoleic acid, 9cis,12trans-18:2, alpha-linolenic acid, and 9cis,12cis,15trans-18:3 were, respectively, 14.0 +/- 4.1%, 24.7 +/- 6.7%, 23.6 +/- 3.3%, and 23.4 +/- 3.7% of the oral load, showing that isomerization increases the postprandial oxidation of linoleic acid but not alpha-linolenic acid in men.

TRANS: isomers of alpha-linolenic acid, which are formed by deodorization of refined vegetable oils, can be found in significant amounts in edible oils. Effects of trans alpha-linolenic acid on plasma lipoproteins are unknown. We therefore investigated the effects of trans alpha-linolenic acid on plasma lipids and lipoproteins in healthy European men. Eighty-eight healthy men from three European countries (France, Scotland, UK and the Netherlands) first consumed for 6 weeks a diet with experimental oils 'free' of trans fatty acids (run-in period). For the next 6 weeks, they were randomly allocated to a diet with experimental oils 'high' or 'low' in trans alpha-linolenic acid. Daily total trans alpha-linolenic acid intake in the high trans group was 1410 (range 583-2642) mg. Experimental oils were provided as such, or incorporated into margarines, cheeses, muffins and biscuits. The high trans alpha-linolenic acid diet significantly increased the plasma LDL-:HDL-cholesterol ratio by 8.1 % (95 % CI 1.4, 15.3; and the total cholesterol:HDL-cholesterol ratio by 5.1 % (95 % CI 0.4, 9.9; compared with the low-trans diet. This was largely explained by an increase in LDL-cholesterol on the high-trans diet, while no change was observed in the low-trans group (mean treatment effect of 4.7 % (95 % CI -0.8, 10.5; No effects were found on total cholesterol and HDL-cholesterol, triacylglycerols, apolipoprotein B and A-1, and lipoprotein(a) concentrations. In conclusion, trans alpha-linolenic acid may increase plasma LDL-:HDL-cholesterol and total cholesterol:HDL-cholesterol ratios. Whether diet-induced changes in these ratios truly affects the risk for CHD remains to be established.

The aim of this study was to investigate the effect of trans alpha-linolenic acid on platelet aggregation and blood haemostasis. A randomized, double blind dietary intervention trial was carried out with healthy male volunteers (n=88) in three European centers. After a 6-week washout period where subjects avoided foods containing all trans fats, subjects either continued for 6 weeks with a low trans diet or a diet where trans alpha-linolenic acid provided 0.6% of energy (supplied as oil, margarine, cheese, muffins, and biscuits). At the end of the washout period the intake of trans polyunsaturated fats was 58+/-115 mg/day; this increased in patients on the high trans diet by +1344+/-328 mg/day, compared with +10+/-67 mg/day in patients on the low trans diet (p<0.01). The change in trans alpha-linolenic acid in plasma cholesteryl esters was 0.26+/-0. 20 on the high trans and 0.00+/-0.07% of fatty acids on the low trans diet (p<0.001). No effect of the high trans diet was observed on platelet aggregation: collagen EC(50) high trans 157+/-100, low trans 152+/-90 ng/mL (NS); U44619 EC(50) high trans 81+/-61, low trans 59+/-27 nM (NS). The high trans diet did not affect platelet thromboxane production, fibrinogen levels, factor VII, activated factor VIIa, or plasminogen activator inhibitor activity. There were no center-specific differences in response to the high trans diet. A relatively high amount of trans alpha-linolenic acid for 6 weeks does not increase the risk of coronary heart disease by promoting platelet aggregation and blood coagulation.

To study the influence on lipid metabolism and platelet aggregation of the fatty acid isomerization that occurs during heat treatment, weanling rats were fed for 8 wk a diet enriched with 5% isomerized (experimental group) or normal (control group) canola oil. Geometrical isomers of alpha-linolenic acid representing 0.2 g/100 g of the experimental diet were incorporated into liver, platelets, aorta and heart, at the expense of their cis homologue and of 18:2(n-6). The major isomer, 9c,12c,15t-18:3, was also metabolized to 5c,8c,11c,14c,17t-20:5 and to an unknown compound, found in liver, platelets and aorta, which has been identified tentatively as 7c, 10c,13c,16c,19t-22:5. The greater 20:4(n-6)/18:2(n-6) ratio in the liver, platelets and heart of the experimental group than the control group indicated an enhancement of desaturation activities. This induced a higher content of long-chain (n-6) fatty acids in the experimental group. Platelet aggregation tended to be slightly higher (P: = 0.065) in the experimental group. We conclude that 0.2 g of trans isomers of alpha-linolenic acid per 100 g of diet was sufficient to be incorporated and metabolized, thus altering the fatty acid profile of rat tissues.

Several grams of labelled trans linoleic and linolenic acids with high chemical and isomeric purities (>97%) have been prepared for human metabolism studies. A total of 12.5 g of (9Z, 12E)-[1-(13)C]-octadeca-9,12-dienoic acid and 6.3 g of (9Z,12Z, 15E)-[1-(13)C]-octadeca-9,12,15-trienoic acid were obtained in, respectively, seven steps (7.8% overall yield) and 11 steps (7% overall yield) from 7-bromo-heptan-1-ol. The trans bromo precursors used for the labelling were synthesised by using copper-catalysed couplings. The trans fatty acids were then obtained via the nitrile derivatives. A total of 23.5 g of (9Z,12Z)-[1-(13)C]-octadeca-9, 12-dienoic acid and 10.4 g of (9Z,12Z,15Z)-[1-(13)C]-octadeca-9,12, 15-trienoic acid were prepared in five steps in, respectively, 32 and 18% overall yield. Large quantities of bromo and chloro precursors were synthesised from the commercially available acid according to Barton's procedure. In all cases, the main impurities (>0.5%) of each labelled fatty acid have been characterised.

Objective: To collect (i) baseline data and (ii) execute a large multicentre study examining the effect of trans alpha-linolenic acid on its incorporation into plasma lipids and on risk factors for coronary heart disease., Design: Male volunteers were recruited and the habitual diet assessed by a 4-d weighed record. Fatty acid composition of plasma and platelet lipids were determined by gas chromatography at baseline. After a 6 week run-in period on a trans 'free' diet, male volunteers were randomised to consume 0.6 % of energy trans alpha-linolenic acid or to continue with a diet 'low' in trans alpha-linolenic acid for 6 weeks., Setting: Three European university research departments supported by the research and development departments of the food industry., Subjects: Male volunteers (88) recruited by local advertisement., Methods: Replacement of 30 % of the fat of the habitual diet by margarine, oil and foods. Rapeseed oil was deodorised especially to produce the trans 'free' and 'high' trans foods for this study. The incorporation and conversion of trans alpha-linolenic acid into plasma lipids and platelets was assessed by gas chromatography and dietary compliance was verified by 4-d weighed record., Results: Less trans alpha-linolenic acid isomers are incorporated into human plasma lipids in French volunteers than in Dutch or Scottish volunteers consuming their habitual diets. Trans 'free' alpha-linolenic acid-rich oil can be produced by careful deodorization during refining. The 'high' trans diet provided 1410+/-42 mg/d trans isomers of alpha-linolenic acid, whilst the 'low' trans group consumed 60+/-75 mg/d. The change in plasma lipid and platelet fatty acid composition documented that trans linolenic isomers are incorporated and converted to a trans isomer of eicosapentaenoic acid. Only the 15-trans alpha-linolenic acid is incorporated into plasma cholesteryl esters. The group consuming low trans diet had a slightly higher intake of fat, especially saturated and monounsaturated fat., Conclusions: Trans 'free' rapeseed oil, rich in alpha-linolenic acid, can be produced by careful deodorization. Dietary records show good compliance. Dietary trans isomers of alpha-linolenic acid are incorporated in plasma lipids and converted to long-chain polyunsaturated fatty acids. Their effects on risk factors for coronary heart disease and their metabolism will be reported elsewhere., Sponsorship: European Commission (FAIR 95-0594 grant). European Journal of Clinical Nutrition (2000) 54, 104-113

Trans polyunsaturated fatty acids are formed during processing of vegetable oils such as deodorization and frying. The oxidative metabolism of linoleic and alpha-linolenic acids and of their mono-trans isomers (9cis,12trans-18:2, 9trans,12cis-18:2 and 9cis, 12cis,15trans-18:3, 9trans,12cis,15cis-18:3, respectively) was studied in fasting rats. A single dose of 18.5 MBq of each [1-14C] labelled fatty acid (260 microg) was orally given to the animals. The 14CO2 expired was monitored during 24 h. Radioactive countings of the CO2-trapping agent were performed at regular intervals up to 24 h after oral administration of the radiolabelled fatty acid. Radioactive countings were also performed on several tissues (liver, heart, brain, kidneys, sus-epidydimal fat, gastrocnemian muscle, gastrointestinal tract and carcass). The 14CO2 production 24 h after oral administration of the fatty acid ranged from 55.5% to 68.7% of the radioactivity administered for the C18:2 isomers and from 69.7% to 73.5% for the C18:3 fatty acids. From 6 to 24 h, 14CO2 recovery was significantly higher after oral administration of 9cis, 12trans-18:2 than after giving both other octadecadienoic isomers. 14C retention per gram of tissue in the liver and in the heart was significantly lower after feeding 9cis,12trans-18:2 than after administration of both other C18:2 isomers. 14C retention per gram of tissue in the muscle was significantly lower after administration of both trans C18:2 isomers compared to linoleic acid. Neither 14CO2 recoveries nor 14C retentions were significantly different after administration of the three octadecatrienoic acids. The difference observed in 14CO2 recovery within the dienes was probably not due to a higher specificity of the enzymes involved in the beta-oxidation sequence for the Delta12trans double bond, as previously reported. Indeed, due to the labelling of the fatty acids on the carboxyl end, 14C values recorded in the CO2-trapping agent were only due to the first cycle of beta-oxidation., (Copyright 1998 Elsevier Science B.V.)