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

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 compositi on, we conducted a 93-d study with 17 healthy female volunteers at the Meta bolic Research Unit of the Western Human Nutrition Research Center. Through out the study, subjects were fed a low-fat diet. [30 energy percent (en%) f at, 19 en% protein, and 51 en% carbohydrate] that consisted of natural food s with the recommended dietary allowances for all known nutrients. After a 30-d stabilization period, subjects were randomly assigned to either an int ervention 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 sun flower oil. The CLA capsules (CLA 65%) contained four major cis/trans geome tric 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 corresp onding cis/cis (6.74% total) and trans/trans (5.99% total) varieties in sma ller amounts. Fasting blood was drawn on study days 30 (end of the stabiliz ation 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 cholester ol, low density lipoprotein cholesterol, high density lipoprotein cholester ol, and triglycerides. The weight percentage of CLA in plasma increased fro m 0.28 +/- 0.06 to 1.09 +/- 0.31 (n = 10, P < 0.05) after the supplementati on. The 9 cis-,ll trans-isomer was the most prominent variety followed by t he 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 <plus/minus > 10.18 to 0.83 +/- 0.19 wt%) (n = 10) and the 9 cis-,ll trans-variety was the only isomer present. Thus, contrary to findings from some animal studie s, 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, norm olipidemic 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.