Conjugated Linoleic Acid (CLA) is a unique fatty acid found in ruminant animal and dairy fats. Ruminant animals are hooved and digest food in two phases such as cattle and sheep. CLA has only been known for two decades. The form of CLA found most commonly in dietary supplements is manufactured from vegetable oils such as sunflower oil or safflower oil.

Conjugated Linoleic Acid Benefits

        • Builds muscle 
        • Prevents muscle loss
        • Burns fat 
        • Increases metabolic rate
        • Fights cancer 
        • Antioxidant
        • Increases the immune system
        • Lowers cholesterol and triglycerides  
        • Lowers insulin resistance  
        • Reduces food-induced allergic reactions

Theory

CLA is also theorized to modulate the production of prostaglandins, which in turn increase growth hormone.  Increased growth hormone levels promote enhanced muscle growth, strength and fat loss. Some prostaglandins may also increase blood circulation to the muscles and adipose tissue - an effect that has been suggested to improve muscle function and fat mobilization.

Scientific Support

An analysis of the best research studies on CLA (13 studies in peer-reviewed journals) did not show a change in body weight but three of the studies showed a decrease in fat mass. The conclusion of the review was that CLA supplementation was not recommended. Ref: http://www.jlr.org/cgi/reprint/R300011-JLR200v1.pdf

Cost 

 A month’s supply of CLA is anywhere from $11-90.

Conclusion

Due to the lack of efficacy and the safety risks, I do not recommend taking CLA in supplement form. The reason is that the supplement preparations contain a high amount of the trans-10/cis-12 isomer which has been linked to adverse effects. However, when you eat food that contains CLA (beef, milk, cheese, buffalo, goat etc.) there is very little of the trans-10/cis-12 isomer.

The main isomer of CLA in food is isomer c9,t11 which appears to be safe. CLA found in food may be very beneficial in other areas besides weight loss (see "Claims" listed above).

Keep in mind that CLA is only found in high amounts in animals that have been raised naturally on grass-fed pastures. Most cattle are raised on corn to make them fat which is not a favorable diet for cows and results in a much lower nutritional content of the meat and dairy including greatly reduced amounts of CLA. If you eat beef and dairy I recommend that you buy grass-fed organic meat and dairy instead of conventional for all the added health benefits.

An increasing amount of studies have shown CLA having adverse effects such as insulin resistance, inflammation, and decreased milk fat production in lactating women. These adverse effects are especially correlated with the form of CLA called the trans-10/cis-12 isomer. One of the human trials reported that about 30% of subjects reported gastrointestinal symptoms associated with recommended doses (3-5 grams/day). Some people may benefit from 1,000 mg three times a day with meals.