Conjugated linoleic acid, or CLA, is a fatty acid found in meat and dairy products. As a supplement, it has been marketed primarily as a weight-loss aid. Animal studies suggest that CLA may have other health benefits, but human studies haven't shown the same benefits.
Technically, CLA is a trans fat, but naturally occurring trans fats aren't harmful to health as industrially produced trans fats may be. CLA comes in about 28 different isomers. Isomers are formed with the same chemical formula but with different characteristics.
CLA supplements don't come from animal products but are created from oils high in linoleic acid, including soybean, safflower, sunflower, and corn oils. Supplements made from these oils have a different mixture of isomers than naturally occurring CLA. For this reason, CLA supplements may not provide the same benefits as CLA from food.
Evidence is a little stronger for these health benefits of CLA:
Scientists working with mice found that CLA appeared to reduce tumor growth in several types of cancer. These conclusions were somewhat supported by studies that found that women who consume a lot of dairy, which contains CLA, have a lower risk of breast and colorectal cancer.
When researchers carried out clinical trials on people with cancer, their results were mixed. More research is needed before CLA supplements can be considered a proven cancer fighter.
Weight Loss Aid
CLA appears to promote weight loss in animals. Scientists believe that it may promote the breaking down of fat and slow down the creation of fat. Some human trials have resulted in modest reductions in body fat.
Other studies have not shown this effect. Scientists believe that differences in results may be due to the use of different CLA isomers at varying dosages.
CLA is generally well-tolerated. Some of those taking CLA supplements report digestive problems such as nausea, vomiting, diarrhea, constipation, stomach pains, and indigestion.
In addition, CLA supplements have been associated with some health risks, including these:
A meta-analysis of 14 studies found that taking CLA supplements increases the amount of C-reactive protein (CRP) in the blood. CRP is a marker for inflammation that may predict an increased risk of cardiovascular disease (heart problems).
Lower Levels of Good Cholesterol
Some studies show that CLA supplementation has no effect on cholesterol levels. Other study subjects had lower levels of HDL cholesterol, the "good" cholesterol. The different results could be because researchers used different CLA isomers.
Poor Blood Sugar Control
One CLA isomer has increased insulin resistance in men with metabolic syndrome, or a series of risk factors which increase their risk for heart disease. Those with diabetes should not take CLA supplements because it could lead to poor blood sugar control.
Amounts and Dosage
Typical doses for CLA are 2.4–6 grams daily. These doses have been used for up to 12 months with few safety concerns.
CLA is found in products derived from ruminant animals such as cattle, sheep, and goats. It is found in both meat and dairy products such as butter.
Several factors can change the CLA content of animal products. One is the animal feed. Products from animals fed on grass and corn have a higher CLA level. The age and breed of the animal also play a role. Animals also have higher CLA content during the spring and summer.