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What is it?
Conjugated linoleic acid (CLA) is a slightly altered form of the essential fatty acid linoleic acid.
Where is it found?
CLA is found mainly in dairy products and also in beef and poultry, eggs, and corn oil. Bacteria that live in the intestine of humans can produce CLA from linoleic acid, but supplementation of a rich source of linoleic acid did not produce increases in blood levels of CLA in one human study.1 CLA is available as a supplement.
What do the advocates say?*
Research suggests that conjugated linoleic acid (CLA) may help to reduce body fat and increase muscle. The research supporting CLA’s ability to help reduce body fat is good, but more is needed. There are at least seven human studies (two are double-blind and the others are controlled) showing significant reduction of abdominal obesity and body fat mass in overweight and moderately obese people. However, since most of the studies involved a small number of participants and were short in duration, larger double-blind studies are needed to further document the benefits and mechanisms of action.
Although CLA promotes weight loss, which is good for heart health, it is important to moniter cholesterol levels as it may reduce HDL (“good”) cholesterol.
How much is usually taken by dieters?
A double-blind trial found that exercising individuals taking 1,800 mg per day of CLA lost more body fat after 12 weeks than a similar group taking a placebo.2 However, two other studies found that amounts of CLA from 0.7 to 3.0 grams per day did not affect body composition.3 4 Most double-blind trials have found that larger amounts of CLA, 3.4 to 4.2 grams per day, does reduce body fat;5 6 7 however, one double-blind study of experienced strength-training athletes reported no effect of 6 grams per day of CLA on body fat, muscle mass, or strength improvement.8
Are there any side effects or interactions?
Overweight volunteers who took 4.5 grams of CLA per day for one year had an increase in their blood levels of lipoprotein(a), a risk factor for heart disease.9 While the significance of this change is not certain, it is possible that long-term use of CLA could increase the risk of developing heart disease.
In a double-blind study of people with type 2 diabetes, supplementing with 3 grams of CLA per day for eight weeks significantly increased blood glucose levels by 6.3% and decreased insulin sensitivity.10 A reduction in insulin sensitivity was also seen in a study of overweight men without diabetes after treatment with 3 grams of CLA per day for three months,11 although in a study of young sedentary men, 4 grams of CLA per day for eight weeks improved insulin sensitivity.12 Thus, although the studies are conflicting, CLA may be harmful for some people who have, or are at risk of developing, diabetes. One unpublished human trial reported isolated cases of gastrointestinal upset.13
At the time of writing, there were no well-known drug interactions with conjugated linoleic acid.
*Dieters and weight-management advocates may claim benefits for CLA based on their personal or professional experience. These are individual opinions and testimonials that may or may not be supported by controlled clinical studies or published scientific articles on CLA. For more complete and detailed information, including references and safety information, see CLA as a nutritional supplement.
References
1. Herbel BK, McGuire MK, McGuire MA, et al. Safflower oil consumption does not increase plasma conjugated linoleic acid concentrations in humans. Am J Clin Nutr 1998;67:332–7.
2. Thom E, Wadstein J, Gudmundsen O. Conjugated linoleic acid reduces body fat in healthy exercising humans. J Int Med Res 2001;29:392–6.
3. Mougios V, Matsakas A, Petridou A, et al. Effect of supplementation with conjugated linoleic acid on human serum lipids and body fat. J Nutr Biochem 2001;12:585–94.
4. Zambell KL, Keim NL, Van Loan MD, et al. Conjugated linoleic acid supplementation in humans: effects on body composition and energy expenditure. Lipids 2000;35:777–82.
5. 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;25:1129–35.
6. Smedman A, Vessby B. Conjugated linoleic acid supplementation in humans—metabolic effects. Lipids 2001;36:773–81.
7. Blankson H, Stakkestad JA, Fagertun H, et al. Conjugated linoleic acid reduces body fat mass in overweight and obese humans. J Nutr 2000;130:2943–8.
8. Kreider RB, Ferreira MP, Greenwood M, et 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;16:325–34.
9. 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;79:1118–25.
10. 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;80:887-95.
11. Riserus U, Vessby B, Arnlov J, Basu S. Effects of cis-9,trans-11 conjugated linoleic acid supplementation on insulin sensitivity, lipid peroxidation, and proinflammatory markers in obese men. Am J Clin Nutr 2004;80:279–83.
12. Eyjolfson V, Spriet LL, Dyck DJ. Conjugated linoleic acid improves insulin sensitivity in young, sedentary humans. Med Sci Sports Exerc 2004;36:814–20.
13. Thom E. A pilot study with the aim of studying the efficacy and tolerability of Tonalin CLA on the body composition in humans. Lillestrom, Norway: Medstat Research Ltd., July 1997 [unpublished].
