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.
CLA has been used in
connection with the following conditions (refer to the individual
health concern for complete information):
Who is likely to be deficient?
No deficiencies of CLA are reported or believed to occur, since it is not an essential
nutrient.
How much is usually taken?
Animal research uses very large amounts, equivalent to several grams per day for humans.
Until human research is conducted with CLA, the appropriate amount to take of this nutrient
remains unclear.
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.2 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.3 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.4 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.5 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,6 although in a study
of young sedentary men, 4 grams of CLA per day for eight weeks improved insulin
sensitivity.7 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 One unpublished human trial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.8
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. 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.
3. 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.
4. Taylor JS, Williams SR, Rhys R, et al. Conjugated linoleic acid
impairs endothelial function. Arterioscler Thromb Vasc Biol 2006;26:307–12.
5. 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.
6. 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.
7. Eyjolfson V, Spriet LL, Dyck DJ. Conjugated linoleic acid improves
insulin sensitivity in young, sedentary humans. Med Sci Sports Exerc
2004;36:814–20.
8. 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].