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This article is an extract from my book Griffiths' Sport Supplement Review and is protected by copyright. Permission is given to copy this article on other websites as long as this statement is included with a link back to this site.

Conjugated Linoleic Acid

Other names

Bovinic acid
Cis-9,trans-11 conjugated linoleic acid
Rumenic acid
Trans-10,cis-12 conjugated linoleic acid

What is it?

Conjugated linoleic acid (CLA) is a polyunsaturated fatty acid which occurs naturally in many foods particularly those from ruminant animals such as beef and dairy products. The body cannot synthesize its own CLA.

There are 28 known isomers (different forms) of CLA, however only two forms have been shown to possess biological activities. These are the cis-9, trans-11 and trans-10, cis-12 forms (1). In natural food sources the cis-9, trans-11 isomer predominates by 30-70:1 (2) however CLA supplements are usually produced by processing plant oils such as safflower which results in a product containing high levels of both the cis-9, trans-11 and the trans-10,cis-12 isomers.

Claimed benefits

Improved body composition, less fat and more lean muscle mass.

Mode of Action

Evidence from animal and cell studies suggests that the cis-9, trans-12 isomer is the form responsible for anabolic effects and increases in muscle mass whilst the trans-10, cis-12 isomer is the form which causes increased lipolysis and fat oxidation.

CLA affects enzymes regulating fat metabolism causing reduced fat storage in adipocytes (fat storage cells), and increased mobilization and oxidation of fats for energy. It also seems to reduce adipocyte proliferation and induces apoptosis (cell death) of developing adipocytes (2).


CLA has been shown to be effective in animal studies and has reduced body fat percentage in animals such as mice, rats and pigs. Mice seem to respond best to CLA with 40%-80% reductions in body fat mass being observed when CLA composed 0.5% of their diet (2). In mice CLA has been shown to decrease fat mass while simultaneously increasing muscle mass (3) (4) (5).

In humans one or two small studies have shown no benefit from CLA supplementation (6). The results of other studies have been underappreciated on the grounds that CLA did not reduce overall bodyweight or BMI even though fat mass was significantly reduced, which strongly indicates a concomitant increase in lean mass.

However as more recent and larger studies have been published using more accurate methods of fat measurement the weight of evidence has shifted squarely in favour of the beneficial effect of CLA on body composition.

For example a year long double blind study looked at 180 healthy but overweight men and women randomized to receive either placebo or 4.5g CLA daily (equivalent to approximately 3.6g of active isomers as a 50:50 mixture of cis-9, trans-11 and trans-10, cis-12 isomers). After 12 months the CLA group had approximately 7-8% less body fat mass than the placebo group (as measured by the accurate dual-energy X-ray absorptiometry method) and approximately 2% more lean body mass (7).

In a follow on study 134 of the original participants in the above study were then given a 4.5g daily dose of CLA (regardless of whether they had originally received CLA or a placebo) for a further 12 months. The individuals originally taking a placebo then had an average reduction in body fat mass of approximately 6%. The people who had already been taking CLA maintained their reduction in body fat mass but did not lose any more (8).

A later double blind, placebo-controlled trial involving 118 people also looked at which body site CLA caused the greatest reduction in fat mass, comparing arms, legs and abdomen. After 6 months supplementation with a similar quantity and type of CLA as used in the studies above body fat mass was significantly reduced by 3·4% after 6 months supplementation with CLA compared with placebo. The reduction in fat mass was located mostly in the legs and women had more loss than men. There was also a significant reduction in the waist/hip ratio (9).

Other smaller studies in obese individuals have shown similar results regarding loss of fat mass (10) (11) and gain in lean body mass (12).

Studies on non-obese healthy exercising humans have also shown a beneficial but small effect of CLA. For example in a randomised double blind study of 76 men and women supplemented with 5g daily of CLA and undertaking resistance training for 14 weeks a statistically significant reduction in fat mass of 4% and an increase in lean body mass of 2.3% was seen. Most of the participants had more than 2 years of resistance training experience and had been training at least two times per week for a minimum of 3 months before involvement in the study (13).

Other studies with exercising individuals have seen similar results (14) (15).

In conclusion CLA supplementation will probably lead to modest reductions in body fat mass and modest increases in lean body mass.

Commonly used dosages

CLA is commonly found in meal replacement formulas and bars in doses from 1000mg to 1500mg.

It is also sold as a stand alone supplement often in capsules of 1000mg containing between 70%-80% CLA.


CLA did not produce serious adverse effects in the studies mentioned above when taken for periods up to 24 months.

The most common adverse effects reported were gastrointestinal upset including nausea and diarrhea.

There is some concern that the isolated trans-10,cis-12 isomer of CLA can increase insulin resistance which can be a risk factor for or worsen diabetes or the metabolic syndrome. It is not known if commercial supplements containing mixed isomers have the same effect (16) (17).


None known.


1) Banni S. Conjugated linoleic acid metabolism. Curr Opin Lipidol. 2002;13(3):261-6
2) Wahle KW, Heys SD, Rotondo D. Conjugated linoleic acids: are they beneficial or detrimental to health? Prog Lipid Res. 2004;43(6):553-87
3) DeLany JP, Blohm F, Truett AA, Scimeca JA, West DB. Conjugated linoleic acid rapidly reduces body fat content in mice without affecting energy intake. Am J Physiol. 1999;276(4 Pt 2):R1172-9
4) West DB, Delany JP, Camet PM, Blohm F, Truett AA et al. Effects of conjugated linoleic acid on body fat and energy metabolism in the mouse. Am J Physiol. 1998;275(3 Pt 2):R667-72
5) Park Y, Albright KJ, Liu W, Storkson JM, Cook ME et al. Effect of conjugated linoleic acid on body composition in mice. Lipids. 1997;32(8):853-8
6) Zambell KL, Keim NL, Van Loan MD, Gale B, Benito P et al. Conjugated linoleic acid supplementation in humans: effects on body composition and energy expenditure. Lipids. 2000;35(7):777-82
7) Gaullier JM, Halse J, Høye K, Kristiansen K, Fagertun H et al. Conjugated linoleic acid supplementation for 1 y reduces body fat mass in healthy overweight humans. Am J Clin Nutr. 2004;79(6):1118-25
8) Gaullier JM, Halse J, Høye K, Kristiansen K, Fagertun H 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(4):778-84
9) Gaullier JM, Halse J, Høivik HO, Høye K, Syvertsen C et al. Six months supplementation with conjugated linoleic acid induces regional-specific fat mass decreases in overweight and obese. Br J Nutr. 2007 Mar;97(3):550-60
10) Risérus 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(8):1129-35
11) Blankson H, Stakkestad JA, Fagertun H, Thom E, Wadstein J et al. Conjugated linoleic acid reduces body fat mass in overweight and obese humans. J Nutr. 2000 Dec;130(12):2943-8
12) Steck SE, Chalecki AM, Miller P, Conway J, Austin GL et al. Conjugated linoleic acid supplementation for twelve weeks increases lean body mass in obese humans. J Nutr. 2007;137(5):1188-93
13) Pinkoski C, Chilibeck PD, Candow DG, Esliger D, Ewaschuk JB et al. The effects of conjugated linoleic acid supplementation during resistance training. Med Sci Sports Exerc. 2006;38(2):339-48
14) Thom E, Wadstein J, Gudmundsen O. Conjugated linoleic acid reduces body fat in healthy exercising humans. J Int Med Res. 2001 Sep-Oct;29(5):392-6
15) Kreider RB, Ferreira MP, Greenwood M, Wilson M, Almada AL. Effects of conjugated linoleic acid supplementation during resistance training on body composition, bone density, strength, and selected hematological markers. J Strength Cond Res. 2002;16(3):325-34
16) Risérus U, Smedman A, Basu S, Vessby B. Metabolic effects of conjugated linoleic acid in humans: the Swedish experience. Am J Clin Nutr. 2004 Jun;79(6 Suppl):1146S-1148S
17) Risérus U, Arner P, Brismar K, Vessby B. Treatment with dietary trans10cis12 conjugated linoleic acid causes isomer-specific insulin resistance in obese men with the metabolic syndrome. Diabetes Care. 2002 Sep;25(9):1516-21

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