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):
Reliable
and relatively consistent scientific data showing a substantial health benefit. Contradictory, insufficient, or preliminary studies
suggesting a health benefit or minimal health benefit. For an herb, supported by traditional use but minimal
or no scientific evidence. For a supplement, little scientific support and/or minimal health
benefit.
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 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.7 Moreover, in a
study of young sedentary men, 4 grams of CLA per day for eight weeks improved insulin
sensitivity.8 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.9
At the time of writing, there were no well-known drug interactions
with conjugated linoleic acid.
References (To view, roll mouse over the "References" heading; to hide, click on the heading)
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. 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.
9. 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].
The information presented in Healthnotes is for informational purposes
only. It is based on scientific studies (human, animal, or in vitro), clinical
experience, or traditional usage as cited in each article. The results reported may not
necessarily occur in all individuals. For many of the conditions discussed, treatment with
prescription or over the counter medication is also available. Consult your doctor,
practitioner, and/or pharmacist for any health problem and before using any supplements or
before making any changes in prescribed medications. Information expires June 2009.
Reliable
and relatively consistent scientific data showing a substantial health benefit.
Contradictory, insufficient, or preliminary studies
suggesting a health benefit or minimal health benefit.