Conjugated linoleic acid (CLA) is attracting interest because of its purported effects on body composition, specifically a reduction in body fat mass and an increase in lean body mass. Other reported beneficial health-related effects of CLA include anticarcinogenic, antiatherogenic, antidiabetogenic, and immune modulating properties. Because research on CLA has been almost exclusively in animals and the mechanism(s) by which CLA exerts its effects remain largely unknown, scientists are extremely cautious about making definitive statements about CLA. Despite the limited research on CLA in human subjects, numerous Internet websites and health food stores sell CLA supplements or CLA-containing products as weight loss or ergogenic aids. The increasing popularity of CLA as a dietary supplement makes it important that dietitians and health professionals are aware of CLA and are able to provide the public with science-based information regarding CLA.