cla

CLA (conjugated linoleic acid) is a group of naturally occurring fatty acids — isomers of linoleic acid — found mainly in the milk and meat of ruminant animals such as cattle, where they are produced by microbes in the animal's gut. It is sold as a dietary supplement, and commercial versions are typically made from plant oils such as safflower oil and contain a mix of CLA isomers (commonly a roughly 50:50 blend of the c9,t11 and t10,c12 forms).

Human evidence for CLA is weak. While CLA reduces body fat in animal studies, the U.S. National Institutes of Health Office of Dietary Supplements (ODS) states that in human studies its effects are "small and of questionable clinical relevance," and results across trials are mixed. Some randomized trials and meta-analyses report only minor average reductions in body weight and fat that may not be clinically meaningful. There is no reliable evidence that CLA produces meaningful, lasting weight loss, and no good evidence that it treats or prevents cholesterol problems, cancer, or any other disease in people.

There is no established effective dose of CLA for weight loss or any health condition, and products vary widely in strength and in their mix of CLA isomers. Doses of roughly 2.4 to 6 grams per day for up to 12 months have been studied with few safety concerns reported, but this does not mean such doses are proven to work. Because the human benefit is unproven and CLA may worsen blood sugar and some blood-lipid markers, talk to a clinician or pharmacist before taking it, especially if you have diabetes, heart disease, or take other medications.

CLA appears to be generally well tolerated at studied doses, but it is not risk-free. According to NIH ODS, the t10,c12-CLA isomer has been reported to increase insulin resistance and blood glucose in men with obesity and metabolic syndrome, so it may be inappropriate for people who have or are at risk of diabetes. Effects on blood lipids are inconsistent: some studies show no major effect, but others suggest certain CLA isomers may lower HDL ("good") cholesterol and raise lipoprotein(a), so people with heart disease or cardiovascular risk factors should be cautious. CLA may also increase some markers of oxidative stress and reduce the fat content of breast milk, though more research is needed to confirm these effects. Pregnant or breastfeeding people should avoid CLA supplements unless advised otherwise by a clinician.

The most commonly reported side effects are gastrointestinal, including abdominal discomfort and pain, constipation, diarrhea, loose stools, nausea, vomiting, and indigestion (dyspepsia). As noted under safety, CLA may also adversely affect blood-glucose control and certain blood-lipid markers in some people.

No specific drug interactions are well established. However, because some CLA isomers may raise blood glucose and reduce insulin sensitivity, CLA could work against the goals of diabetes medications and should be used cautiously by anyone managing blood sugar. As with any supplement, tell all of your healthcare providers that you take CLA so they can check for potential conflicts with your medications.