The effect of conjugated linoleic acid on plasma lipoproteins and tissue fatty acid composition in humans

Abstract

Conjugated linoleic acid (CLA) has been suggested by some animal studies to possess antiatherogenic properties. To determine, in humans, the effect of dietary CLA on blood lipids, lipoproteins, and tissue fatty acid composition, we conducted a 93-d study with 17 healthy female volunteers at the Metabolic Research Unit of the Western Human Nutrition Research Center. Throughout the study, subjects were fed a low-fat diet [30 energy percent (en%) fat, 19 en% protein, and 51 en% carbohydrate] that consisted of natural foods with the recommended dietary allowances for all known nutrients. After a 30-d stabilization period, subjects were randomly assigned to either an intervention group (n = 10) supplemented daily with capsules containing 3.9 g of CLA or a control group (n = 7) that received an equivalent amount of sunflower oil. The CLA capsules (CLA 65%) contained four major cis/trans geometric isomers (11.4% 9 cis-,11 trans-18:2; 10.8% 8 trans-,10 cis-18:2; 15.3% 11 cis-,13 trans-18:2; and 14.7% 10 trans-,12 cis-18:2) and their corresponding cis/cis (6.74% total) and trans/trans (5.99% total) varieties in smaller amounts. Fasting blood was drawn on study days 30 (end of the stabilization period), 60 (midpoint of the intervention period), and 93 (end of the intervention period). Adipose tissue samples were taken on days 30 and 93. CLA supplementation for 63 d did not change the levels of plasma cholesterol, low density lipoprotein cholesterol, high density lipoprotein cholesterol, and triglycerides. The weight percentage of CLA in plasma increased from 0.28 +/- 0.06 to 1.09 +/- 0.31 (n = 10, P < 0.05) after the supplementation. The 9 cis-,11 trans-isomer was the most prominent variety followed by the 11 cis-,13 trans- and 10 trans-,12 cis-isomers in lesser amounts. CLA in adipose tissue was not influenced by the supplementation (0.79 +/- 0.18 to 0.83 +/- 0.19 wt%) (n = 10) and the 9 cis-,11 trans-variety was the only isomer present. Thus, contrary to findings from some animal studies, CLA does not seem to offer health benefits, in the short term, regarding the prevention of atherosclerosis in humans. CLA supplementation for 2 mon did not alter the blood cholesterol or lipoprotein levels of healthy, normolipidemic subjects. The supplementation did increase CLA in the plasma but only 4.23% of the ingested CLA was present in the plasma at any given time. No adverse effect of CLA supplementation was detected in this study.

Association of foods enriched in conjugated linoleic acid (CLA) and CLA supplements with lipid profile in human studies: a systematic review and meta-analysis

“…Our analysis showed that TAG level decreased nonsignificantly after intake of either CLA supplements or CLA-enriched foods, similar to previous studies on either enriched foods or CLA supplements. Some findings suggested that CLA had no significant effect on TAG concentration (11)(12)(13)(14)(15)(16)(17)(18)(19)21,22,(24)(25)(26)(27)(29)(30)(31)(32)(33)(34)36,40,(47)(48)(49)(50)(51)(52)(53)(55)(56)(57)(58)(59) .…”

“…(2001) (58) Seventeen females, healthy normalweight (11) Twenty-five males, healthy overweight and obese (18) 401 males and females, healthy overweight and obese…”

Conjugated linoleic acid (CLA) and obesity

“…A 6.4 g day 21 MI-CLA doses for 12 weeks produced a modest increase in lean mass (0.6 kg) but significant decrease in serum HDL-cholesterol, sodium, hemoglobin, and hematocrit, and significant increases in serum alkaline phosphatase, C-reactive protein, and K-6, and white blood cells. Plasma triacylglycerides (TAG) did not significantly change or decrease compared to placebo in some studies with MI-CLA supplementation 33,59,62,63 . Nevertheless, in another study mean plasma TAG concentration was higher during supplementation with a mixture 85% trans-10,cis-12 CLA than with another mixture 80% cis-9,trans-11 CLA 24 .…”

Os efeitos do ácido linoléico conjugado no metabolismo animal: avanço das pesquisas e perspectivas para o futuro

“…O panorama atual a respeito dos efeitos benéficos do CLA na redução dos lípides sangüíneos e na redução da aterosclerose apresenta resultados positivos em coelhos 71 e alguns em hamsters 72,73 . Em humanos os resultados não são satisfatórios, visto que a maioria dos estudos não demonstra alteração do perfil lipídico [74][75][76] e, quando isto acontece, essas alterações não são benéficas como, por exemplo, aumento na concentração de lipoproteina 77 , redução de HDL colesterol (principalmente pelo isômero trans-10, cis-12) e aumento de triacilglicerol 65,78 , além do aumento de LDL colesterol 79 . Destaca-se que os estudos realizados com humanos apresentam as mais diversas populações e amostragens relativamente pequenas contendo a menor 17 indivíduos 74,76 e a maior 180 indivíduos 77 .…”

“…A partir de então muitos foram os estudos com diversos animais [102][103][104] , com culturas de adipócito de roedores e humanos [105][106][107][108][109] e com humanos 8,65,[74][75][76][77][78][79][80]90,95,96,[110][111][112][113][114][115][116] , que surgiram com o objetivo de avaliar a propriedade de redução da gordura corporal, bem como elucidar os mecanismos de ação pelos quais o CLA desempenha esse papel.…”