Conjugated linoleic acid (CLA) is found in ruminant meats such as beef and lamb and in dairy products such as milk and cheese.
Many studies support the anticancer, antiobesity, antidiabetic, and antiatherogenic properties of CLA (Lee et al 1994; Park et al 1997, 1999; West et al 1998; Yamasaki et al 2003).

Human clinical trials have shown reductions in body fat from CLA supplementation.

Supplementation with 1.8 g daily of CLA for 12 weeks reduced body fat in healthy, exercising humans of normal body weight (Thom et al 2001).

Men with abdominal obesity who consumed 4.2 g daily of CLA for 4 weeks decreased their abdominal diameter (Riserus et al 2001).

Supplementation with 3.4 or 6.8 g of CLA daily for two weeks decreased body fat mass in overweight and obese people, and the trans-10, cis-12 CLA isomer inhibited the activities of the fat-storage enzyme lipoprotein lipase (Pariza et al 2001). The cis-9, trans-11 isomer, a specific isomer of CLA, increases metabolic rate and energy production (thermogenesis) (Ryder et al 2001; Brown et al 2003).

Evidence from a short-term study (12 weeks) has suggested that treatment with CLA may worsen insulin resistance (Riserus et al 2002). However, a long-term study (one year) in overweight and obese men and women has shown that CLA is effective for weight loss with no adverse effects on insulin sensitivity (Gaullier et al 2004). A 36-week toxicity study in animals given CLA at doses far exceeding those given to humans also showed CLA to be without toxicity (Scimeca 1998).