CLA

Conjugated linoleic acid, usually abbreviated CLA, refers not to a single substance but to a family of isomers of linoleic acid, an essential omega-6 fatty acid. What sets these isomers apart is that their two carbon-carbon double bonds are conjugated, meaning separated by a single bond, and they can differ in the position and the cis or trans geometry of those bonds; the two most studied forms are the cis-9,trans-11 isomer (also called rumenic acid) and the trans-10,cis-12 isomer ^[2][3]. Although some CLA isomers are technically trans fats, they are generally not thought to carry the harmful effects associated with industrial trans fats.

CLA occurs naturally in the meat and dairy products of ruminant animals, where it is formed by bacteria in the animals' digestive systems, and grass-fed animals tend to yield more of it than grain-fed ones. Humans can also make a small amount of the cis-9,trans-11 form from vaccenic acid. Interest in CLA as a supplement grew after studies in mice showed that it could substantially reduce body fat ^[2][3].

In people, the results have been far less dramatic than in rodents. A meta-analysis of human trials concluded that CLA produces only a modest loss of body fat, and other reviews found little consistent effect on body weight or blood lipids ^[1][2][3]. A more recent systematic review of CLA combined with exercise reported small reductions in body fat and insulin resistance but no benefit for body weight or exercise performance ^[4]. Overall, health authorities regard the evidence that CLA meaningfully helps with weight or obesity as insufficient.

CLA is sold widely as an over-the-counter dietary supplement, often in softgel capsules, and is typically produced commercially from plant oils such as safflower or sunflower oil rather than extracted from animal fat. In the United States it has been granted generally recognized as safe status for use in certain foods. Reported side effects are usually mild and gastrointestinal ^[4].

Common complaints are GI upset, nausea, and loose stools. More concerning, high-dose t10,c12 CLA has been linked in some studies to reduced insulin sensitivity, fatty liver signs, and lower HDL. It's not something to take long-term at high doses.