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Study Questions Popular CLA Supplement

By Marcia Wood
July 31, 2001

A popular nutritional supplement called conjugated linoleic acid, or “CLA,” may provide more health benefits for animals than for humans. That’s according to findings from a study by scientists with the Agricultural Research Service, the U.S. Department of Agriculture’s chief scientific research agency.

ARS research chemist Darshan S. Kelley at the ARS Western Human Nutrition Research Center at Davis, Calif., and colleagues were unable to find any significant, positive benefits of CLA supplements in their three-month-long test of 17 healthy, nonsmoking women, age 20 to 41.

During the test, the volunteers lived at the research center, formerly located in San Francisco. They ate familiar, everyday foods at mealtimes and for their evening snack. For the first month of the study, all volunteers took sunflower oil capsules with meals. The sunflower oil capsules served as a control--that is, a basis from which a comparison to CLA capsules could be made.

For the second and third months of the study, 10 volunteers ate capsules that provided a daily total of 3.9 grams of CLA. That’s more than 10 times the amount most Americans consume every day from foods like beef and some other meats, or dairy products. The other seven volunteers continued taking the sunflower oil capsules.

In animal studies conducted elsewhere, CLA stimulated the animals’ immune systems, protected against some kinds of cancer, reduced body fat and improved cardiovascular health. In the ARS study, however, Kelley found no significant change in more than a dozen indicators of volunteers’ immune system activity. Colleagues Nancy L. Keim and Marta D. Van Loan of the center found that CLA didn’t reduce volunteers’ body fat or help them build muscle.

In addition, CLA didn’t lower blood-fat levels or improve any of the other health indicators the research team examined.

Kelley suggests that the results might have been different if volunteers had consumed more CLA over a longer period of time. Also, a different mixture of CLA components, called isomers, might have led to a different outcome.