Dietary trans α-linolenic acid does not inhibit Δ5- and Δ6-desaturation of linoleic acid in man

Abstract

Dietary trans monoenes have been associated with an increased risk of heart disease in some studies and this has caused much concern. Trans polyenes are also present in the diet, for example, trans α‐linolenic acid is formed during the deodorisation of α‐linolenic acid‐rich oils such as rapeseed oil. One would expect the intake of trans α‐linolenic acid to be on the increase since the consumption of rapeseed oil in the western diet is increasing. There are no data on trans α‐linolenic acid consumption and its effects. We therefore carried out a comprehensive study to examine whether trans isomers of this polyunsaturated fatty acid increased the risk of coronary heart disease. Since inhibition of Δ6‐desaturase had also been linked to heart disease, the effect of trans α‐linolenic acid on the conversion of [U‐13C]‐labelled linoleic acid to dihomo‐γ‐linolenic and arachidonic acid was studied in 7 healthy men recruited from the staff and students of the University of Edinburgh. Thirty percent of the habitual fat was replaced using a trans ‘free’‐ or ‘high’ trans α‐linolenic acid fat. After at least 6 weeks on the experimental diets, the men received 3‐oleyl, 1,2‐[U‐13C]‐linoleyl glycerol (15 mg twice daily for ten days). The fatty acid composition of plasma phospholipids and the incorporation of 13C‐label into n‐6 fatty acids were determined at day 8, 9 and 10 and after a 6‐week washout period by gas chromatography‐combustion‐isotope ratio mass spectrometry. Trans α‐linolenic acid of plasma phospholipids increased from 0.04 ? 0.01 to 0.17 ? 0.02 and cis ? ‐linolenic acid decreased from 0.42 ? 0.07 to 0.29 ? 0.08 g/100 g of fatty acids on the high trans diet. The composition of the other plasma phospholipid fatty acids did not change. The enrichment of phosphatidyl 13C‐linoleic acid reached a plateau at day 10 and the average of the last 3 days did not differ between the low and high trans period. Both dihomo‐γ‐linolenic and arachidonic acid in phospholipids were enriched in 13C, both in absolute and relative terms (with respect to 13C‐linoleic acid). The enrichment was slightly and significantly higher during the high trans period (P<0.05). Our data suggest that a diet rich in trans α‐linolenic acid (0.6% of energy) does not inhibit the conversion of linoleic acid to dihomo‐γ‐linolenic and arachidonic acid in healthy middle‐aged men consuming a diet rich in linoleic acid.

New insights in health effects oftrans α-linolenic acid isomers in humans

“…This allowed each subject to serve as his own control. Contrary to the animal studies, this study failed to show consistent a inhibitory ef-fect of the trans α-linolenic acid isomers on the desaturation of linoleic acid [16].…”

Metabolism of trans fatty acid isomers

“…Furthermore feeding to humans 18:3 isomers at 0.6% energy did not seem to affect the conversion of n-6 and n-3 fatty acids as no variation of 20:4n-6 and 22:6n-3 were observed under these conditions. The effects of these 18:3 isomers on the Δ6 desaturation of linoleic acid was further studied by Scrimgeour et al, (2001) using 3-oleyl, 1,2-(U-13 C)-labelled linoleic acid (15 mg twice daily for 10 days) in 7 healthy men from the TransLine study (Sebedio et al, 2000). The data indicated that a diet rich in trans α-linolenic acid at 0.6% energy does not inhibit the conversion of linoleic acid to dihomo-γ-linolenic and arachidonic acid in healthy middle-aged men consuming a diet rich in linoleic acid.…”

Modulação e composição de ácidos graxos do leite humano

“…O AGT C18:3n-3 também é capaz de inibir a ∆5-dessaturase e consequentemente impedir a formação de ácido araquidônico 40 . Portanto, os isômeros trans podem inibir a biossíntese de compostos importantes para o organismo humano.…”