Submitted to: Lipids Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2002
Publication Date: N/A
Citation: Interpretive Summary: While animal studies suggest that conjugated linoleic acids (CLAs) may act as anti-carcinogens and weight loss agents, only limited data is available on their effects in humans. The purpose of this study was to study how the human body uses CLAs in comparison to other fatty acids found in the "normal" adult diet. Healthy, adult women were fed a mixture of labeled CLAs and other fats and their uptake and turnover in the blood was followed. The results show not only that the structure of the CLA was related to its rate of uptake into the body, but that the CLAs were 20-25% less well-absorbed than the more common fatty acids found in the U.S. diet. The addition of CLA to the diet was also found to have little influence on the absorption of other fats. In this study, no evidence of nutritional changes/ effects in fat uptake from CLA supplementation was found. This information can help educate the American consumer in his or her decision whether to purchase or not to purchase CLA as a diet supplement and to provide a basis for further research into these interesting fats.
Technical Abstract: Animal studies suggest that conjugated linoleic acid (CLA) has potential health benefits, but no definitive metabolic data are available to support the possibility that it has physiological activity in humans. The purpose of this study was to determine the effect of dietary CLA on oleic, linoleic, and CLA isomers. The subjects were healthy adult women consuming normal and CLA-supplemented (3.7 g/d) diets. A mixture of 10t,12c-18:2-d4, 9c,11t-18:2-d6, 9c-18:1-d8 and 9c,12c-18:2-d2 was fed to each subject, and plasma lipids were analyzed by mass spectrometry. The results show that the CLA isomers were 20-25% less well-absorbed than oleic and linoleic acid and that dietary CLA supplementation had little influence on the metabolism of the deuterium-labeled fatty acids. The CLA isomers were not metabolically equivalent. The largest differences were a four-fold higher incorporation of 10t,12c-18:2-d4 than 9t,11c-18:2-d6 in 1-acyl phosphatidylcholine and a two to three-fold higher incorporation of 9c,11t-18:1-d6 than 10t,12c-18:2-d4 in cholesterol esters. In general, accumulation of 10t,12c-18:2-d4 and 9c,11t-18:2-d6 in plasma lipids was characteristic of cis and trans 18:1 isomers rather than of 18:0, 9c-18:1 or 9c,12c-18:2. Concentrations of labeled metabolites containing a conjugated diene structure were low. The only CLA metabolite present in significant amounts was 6c,10t,12c-18:3-d4. In conclusion, absorption of CLA was less than oleic acid, CLA positional isomers were metabolically different and similar to cis and trans 18:1 isomers. Conversion of CLA to desaturated and elongated polyunsaturated fatty acids was low. The metabolic results from this study suggest small amounts of dietary CLA in human diets would have little positive or negative health or nutritional effect.