Side effects of CLA supplements may include upset stomach, nausea, diarrhea and fatigue and may also exacerbate insulin resistance in people with diabetes or metabolic syndrome, reports WebMD. Allergic reactions, including unexplained rash, swelling and difficulty breathing, are other possible side effects reported with CLA supplements, according to eMedTV.
Conjugated linoleic acid is an essential fatty acid found in animal products, such as milk, beef and other meats, and also in sunflower and safflower oil, states WebMD. Studies show that CLA supplements may help treat obesity by decreasing body fat and helping people feel more full after eating, but they do not lower weight or body mass index.
CLA is also an antioxidant that may have cancer-fighting properties and other health benefits. Studies indicate that women obtaining high levels of CLA from dietary sources have a lower risk of colorectal and breast cancer, but CLA supplements have not been shown to have this effect, according to WebMD. Research has documented an increase in inflammation with the use of CLA supplements, and doctors do not recommend CLA supplements for children or for women who are pregnant or breastfeeding.
CLA from dietary sources is unlikely to cause significant side effects, claims eMedTV. Manufactured supplements are more likely to contain CLA isomers thought to be responsible for negative side effects than naturally occurring CLA found in dairy and meat.