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Conjugated Linoleic Acid
Description:
Conjugated linoleic acid (CLA) is a slightly altered form of the essential fatty acid linoleic acid.
Properties & Uses:
Research suggests that conjugated linoleic acid (CLA) may help reduce body fat and increase muscle strength and size. There are at least seven human studies (two double-blind and some 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 monitor HDL (“good”) cholesterol levels as CLA may reduce them.
Recommended Dietary Allowances:
CLA is a slightly altered form of the essential fatty acid linoleic acid. Animal research suggests an effect of CLA supplementation on reducing body fat.2 3 Controlled human research has reported that 5.6 to 7.2 grams per day of CLA produces only non-significant gains in muscle size and strength in experienced and inexperienced weight-training men.4 5 6 A double-blind study of a group of trained men and women reported reduced body fat in the upper arm after 12 weeks of supplementation with 1.8 grams per day of CLA.7 Further research using more accurate techniques for measuring body composition is needed to confirm these findings.
Food Sources:
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.
Side Effects & 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.8 In a double-blind study of human volunteers, supplementation with 4.2 grams per day of a mixture of cis-9,trans-11 CLA and trans-10,cis-12 CLA for three months increased the concentration of C-reactive protein, another risk factor for heart disease.9 In a study of healthy volunteers, supplementing with 4.5 grams of CLA per day for 12 weeks caused an impairment of blood vessel function (endothelial dysfunction), which is believed to be associated with an increased risk of heart disease.10 Taken together, these findings suggest 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.11 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.12 However, in another study of obese men and women, supplementation with 6 grams of CLA per day for 24 weeks had no significant effect on blood glucose levels or insulin sensitivity.13 Moreover, in a study of young sedentary men, 4 grams of CLA per day for eight weeks improved insulin sensitivity.14 Although the studies are conflicting, it would be prudent for people who have, or are at risk of developing, diabetes to monitor their blood sugar levels during long-term use of CLA. One unpublished human trial reported isolated cases of gastrointestinal upset.15
At the time of writing, there were no well-known drug interactions with conjugated linoleic acid.
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. West DB, Delany JP, Camet PM, et al. Effects of conjugated linoleic acid on body fat and energy metabolism in the mouse. Am J Physiol 1998;275:R667–72.
3. Park Y, Albright KJ, Liu W, et al. Effect of conjugated linoleic acid on body composition in mice. Lipids 1997;32:853–8.
4. Ferreira M, Krieder R, Wilson M. Effects of CLA supplementation during resistance training on body composition and strength. J Strength Conditioning Res 1998;11:280.
5. 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.
6. Lowery LM, Appicelli PA, Lemon PWR. Conjugated linoleic acid enhances muscle size and strength gains in novice bodybuilders. Med Sci Sport Excer 1998;30:S182 [abstract]
7. Thom E, Wadstein J, Gudmundsen O. Conjugated linoleic acid reduces body fat in healthy exercising humans. J Int Med Res 2001;29:392–6.
8. 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.
9. Smedman A, Basu S, Jovinge S, Fredrikson GN, Vessby B. Conjugated linoleic acid increased C-reactive protein in human subjects. Br J Nutr 2005;94:791–5.
10. Taylor JS, Williams SR, Rhys R, et al. Conjugated linoleic acid impairs endothelial function. Arterioscler Thromb Vasc Biol 2006;26:307–12.
11. 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.
12. 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.
13. 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 Oct;42(10):1701–9.
14. Eyjolfson V, Spriet LL, Dyck DJ. Conjugated linoleic acid improves insulin sensitivity in young, sedentary humans. Med Sci Sports Exerc 2004;36:814–20.
15. 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].