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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 a treatment for diabetes.
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Requirements/Sources
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.
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Therapeutic Dosages
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.
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Therapeutic Uses
Preliminary and not entirely consistent evidence suggests that CLA might help you lose fat while retaining muscle, especially if you also engage in exercise.1–4,8,9 The net effect may be an improvement in body composition (ratio of muscle to fat) instead of weight loss. One study provides weak evidence that CLA might specifically reduce abdominal fat.10
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 showed that CLA improved insulin responsiveness in people with type 2 (adult onset) diabetes. However, another double-blind, placebo-controlled study unexpectly found harmful effects.14 At present, therefore, individuals with diabetes should not use CLA except under physician supervision.
Some animal and test tube studies suggest that CLA might help prevent cancer, but the evidence is preliminary and inconsistent. 7,11
A small double-blind trial found weak evidence that CLA might be useful for high cholesterol.13
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Safety Issues
CLA appears to be a generally safe nutritional substance. However, a concern has been raised regarding 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 mother’s 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.
In addition, as noted above, there are concerns that CLA could actual worsen blood sugar control under certain conditions.14
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References
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. et al. 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.
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