Conjugated linoleic acid (CLA) is a mixture of different isomers, or chemical forms, of linoleic acid. Linoleic acid is an essential fatty acid—a type of fat that your body needs for optimum health.
Based on preliminary evidence, CLA has been promoted as a "fat-burning" supplement and as a treatment for diabetes. However, there is little evidence that it works and growing evidence that CLA might actually worsen blood sugar control in people who are overweight.
Although linoleic acid itself is an important nutritional source of essential fatty acids, there is no evidence that you need to get conjugated linoleic acid in your diet. CLA does occur in food, but it would be very difficult to get the recommended dose that way. Supplements are the only practical source.
The typical dosage of CLA ranges from 3 to 5 g daily. As with all supplements taken at this high a dosage, it is important to purchase a reputable brand, as even very small amounts of a toxic contaminant could quickly add up.
While CLA is often recommended for aiding weight loss or improving body composition (ratio of muscle to fat), evidence from studies is conflicting. 1-4,8-10,15-19,24-26,30,32,35,36 One meta-analysis (systematic statistical review) of all the data found minimal benefits at most. 27 Another meta-analysis concluded that, when taken at a dose of 3.2 grams per day, CLA slightly reduces body fat levels. 33 Finally, in one study, a combination of CLA and chromium failed to improve body composition. 34
Note : Some, but not all studies have raised concerns that use of CLA by overweight people could raise insulin resistance and therefore increase risk of diabetes. In addition, it might increase cardiovascular risk in other ways, as described in the Safety Issues .
A 12-week, double-blind, placebo-controlled study of 40 subjects tested CLA as a treatment for people with allergies to birch pollen (a common cause of hay fever ), and found some evidence of benefit. 37
A small double-blind trial found weak evidence that CLA might be useful for high cholesterol. 13
One study failed to find that CLA can enhance immune function. 28
CLA appears to be a generally safe nutritional substance. 20 However, there are some concerns with its use.
During the course of investigations into its effect on fat, CLA was found to act somewhat similarly to some oral medications used for diabetes . This led to research into the possible usefulness of CLA as a treatment for diabetes. In one study, CLA reduced blood sugar levels in diabetic rats as effectively as a standard diabetes treatment. 5 The same researchers also performed a small, double-blind, placebo-controlled trial in humans. The results indicated that CLA improved insulin responsiveness in people with type 2 (adult onset) diabetes. However, several subsequent studies found opposite and rather alarming results: Use of CLA by people with diabetes may worsen blood sugar control; in overweight people without diabetes, CLA might decrease insulin sensitivity, creating a prediabetic state. 14,21-23 In contrast, a study using the most precise method of measuring insulin sensitivity failed to find any harmful effect. 31 Nonetheless, at present, individuals with diabetes or who are at risk for it should not use CLA except under physician supervision.
One study found that CLA impairs endothelial function and another that it increases levels of C-reactive protein; both of these effects suggest a possible increase in cardiovascular risk. 29,32
Concerns have also been raised regarding use of CLA by nursing mothers. A double-blind, placebo-controlled study indicates that use of CLA reduces the fat content of human breast milk. 12 Since infants depend on the fat in breast milk to provide adequate calories and on certain fats to aid proper growth and development, it is probably prudent for nursing mothers to avoid CLA supplements.
Maximum safe dosages of CLA for young children, pregnant women, or those with severe liver or kidney disease have not been determined.
3. Ferreira M, Kreider R, Wilson M, et al. Effects of conjugated linoleic acid (CLA) supplementation during resistance training on body composition and strength [abstract]. J Strength Cond Res. 1997;11:280.
5. Belury MA, Mahon A, Shi L. Role of conjugated linoleic acid (CLA) in the management of type 2 diabetes: evidence from Zucker diabetic (fa/fa) rats and human subjects. Paper presented at: 220th ACS National Meeting; August 20-24, 2000; Washington, DC. Abstract AGFD 26.
10. Riserus U, Berglund L, Vessby B. Conjugated linoleic acid (CLA) reduced abdominal adipose tissue in obese middle-aged men with signs of the metabolic syndrome: a randomised controlled trial. Int J Obes Relat Metab Disord. 2001;25:1129-1135.
13. Noone EJ, Noone EJ, Roche HM, et al. The effect of dietary supplementation using isomeric blends of conjugated linoleic acid on lipid metabolism in healthy human subjects. Br J Nutr. 2002;88:243-251.
14. Riserus U, Arner P, Brismar K, et al. Treatment with dietary trans10cis12 conjugated linoleic acid causes isomer-specific insulin resistance in obese men with the metabolic syndrome. Diabetes Care. 2002;25:1516-1521.
16. Kamphuis MM, Lejeune MP, Saris WH, et al. The effect of conjugated linoleic acid supplementation after weight loss on body weight regain, body composition, and resting metabolic rate in overweight subjects. Int J Obes Relat Metab Disord. 2003;27:840-847.
17. Kamphuis MM, Lejeune MP, Saris WH, et al. Effect of conjugated linoleic acid supplementation after weight loss on appetite and food intake in overweight subjects. Eur J Clin Nutr. 2003;57:1268-1274.
18. Larsen TM, Toubro S, Astrup A. Efficacy and safety of dietary supplements containing conjugated linoleic acid (CLA) for the treatment of obesity-evidence from animal and human studies. J Lipid Res. 2003. [Epub ahead of print]
21. Moloney F, Yeow TP, Mullen A, et al. Conjugated linoleic acid supplementation, insulin sensitivity, and lipoprotein metabolism in patients with type 2 diabetes mellitus. Am J Clin Nutr. 2004;80:887-895.
22. Riserus U, Vessby B, Arner P, et al. Supplementation with trans10 cis12-conjugated linoleic acid induces hyperproinsulinaemia in obese men: close association with impaired insulin sensitivity. Diabetologia. 2004 May 28. [Epub ahead of print]
23. Larsen TM, Toubro S, Astrup A. Efficacy and safety of dietary supplements containing conjugated linoleic acid (CLA) for the treatment of obesity-evidence from animal and human studies. J Lipid Res. 2003. [Epub ahead of print]
26. Gaullier JM, Halse J, Hoye K, et al. Supplementation with conjugated linoleic acid for 24 months is well tolerated by and reduces body fat mass in healthy, overweight humans. J Nutr. 2005;135:778-784.
31. Syvertsen C, Halse J, Hoivik HO, et al. The effect of 6 months supplementation with conjugated linoleic acid on insulin resistance in overweight and obese. Int J Obes (Lond). 2006 Oct 10. [Epub ahead of print]
34. Diaz ML, Watkins BA, Li Y, et al. Chromium picolinate and conjugated linoleic acid do not synergistically influence diet- and exercise-induced changes in body composition and health indexes in overweight women. J Nutr Biochem. 2007 May 23. [Epub ahead of print]
35. Laso N, Brugue E, Vidal J, et al. Effects of milk supplementation with conjugated linoleic acid (isomers cis-9, trans-11 and trans-10, cis-12) on body composition and metabolic syndrome components. Br J Nutr. 2007 Jul 11. [Epub ahead of print]
37. Turpeinen AM, Ylonen N, von Willebrand E, et al. Immunological and metabolic effects of cis-9, trans-11-conjugated linoleic acid in subjects with birch pollen allergy. Br J Nutr. 2008 Jan 2. [Epub ahead of print]
Last reviewed September 2014 by EBSCO CAM Review Board
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