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.
1. Erling T. A pilot study with the aim of studying the efficacy and tolerability of CLA (Tonalin) on the body composition in humans. Liilestrom, Norway: Medstat Research Ltd.; 1997. (Unpublished.)
2. West D. Reduced body fat with conjugated linoleic acid feeding in the mouse. FASEB J. 1997;11:A599.
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.
4. Blankson H, Stakkestad JA, Fagertun H, et al. Conjugated linoleic acid reduces body fat mass in overweight and obese humans. J Nutr. 2000;130:2943-2948.
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.
6. Ip C, Banni S, Angioni E, et al. Conjugated linoleic acid-enriched butter fat alters mammary gland morphogenesis and reduces cancer risk in rats. J Nutr. 1999;129:2135-2142.
7. Chajes V, Lavillonniere F, Ferrari P, et al. Conjugated linoleic acid and the risk of breast cancer. Presented at: European Conference on Nutrition & Cancer; June 21-24, 2001; Lyon, France.
8. Smedman A, Vessby B. Conjugated linoleic acid supplementation in humans—metabolic effects. Lipids. 2001;36:773-781.
9. Thom E. Wadstein J, Gudmundsen O. Conjugated linoleic acid reduces body fat in healthy exercising humans. J Int Med Res. 2001;29:392-396.
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.
11. MacDonald HB. Conjugated linoleic acid and disease prevention: a review of current knowledge. J Am Coll Nutr. 2000;19(2 Suppl):111S-118S.
12. Masters N, McGuire MA, Beerman KA, et al. Maternal supplementation with CLA decreases milk fat in humans. Lipids. 2002;37:133-138.
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.
15. Gaullier JM, Halse J, Hoye K et al. Conjugated linoleic acid supplementation for 1 y reduces body fat mass in healthy overweight humans. Am J Clin Nutr. 2004;79:1118-1125.
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]
19. Malpuech-Brugere C, Verboeket-Van De Venne WP, Mensink RP, et al. Effects of two conjugated linoleic acid isomers on body fat mass in overweight humans. Obes Res. 2004;12:591-598.
20. Whigham LD, O'Shea M, Mohede IC, et al. Safety profile of conjugated linoleic acid in a 12-month trial in obese humans. Food Chem Toxicol. 2004;42:1701-1709.
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]
24. Larsen TM, Toubro S, Gudmundsen O, et al. Conjugated linoleic acid supplementation for 1 y does not prevent weight or body fat regain. Am J Clin Nutr. 2006;83:606-612.
25. Taylor JS, Williams SR, Rhys R, et al. Conjugated Linoleic Acid Impairs Endothelial Function. Arterioscler Thromb Vasc Biol. 2005 Dec 8. [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.
27. Voevodin M, Sinclair A, Gibson R et al. The effect of CLA on body composition in humans: systematic review and meta-analysis. Asia Pac J Clin Nutr. 2005;14(suppl S55).
28. Nugent AP, Roche HM, Noone EJ, et al. The effects of conjugated linoleic acid supplementation on immune function in healthy volunteers. Eur J Clin Nutr. 2005 Apr 13. [Epub ahead of print]
29. Taylor JS, Williams SR, Rhys R, et al. Conjugated Linoleic Acid Impairs Endothelial Function. Arterioscler Thromb Vasc Biol. 2005 Dec 8. [Epub ahead of print]
30. Watras AC, Buchholz AC, Close RN, et al. The role of conjugated linoleic acid in reducing body fat and preventing holiday weight gain. Int J Obes. 2006 Aug 22. [Epub ahead of print]
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33. Whigham LD, Watras AC, Schoeller DA. Efficacy of conjugated linoleic acid for reducing fat mass: a meta-analysis in humans. Am J Clin Nutr. 2007;85:1203-1211.
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]
36. Close RN, Schoeller DA, Watras AC, et al. Conjugated linoleic acid supplementation alters the 6-mo change in fat oxidation during sleep. Am J Clin Nutr. 2007;86:797-804.
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 December 2015 by EBSCO CAM Review Board Last Updated: 12/15/2015