Functions and benefits of conjugated linoleic acid in the human body

New scientific research is increasingly supporting the notion that foods, food ingredients and ingredient components play a major role in reducing the risk of disease and addressing specific conditions such as high cholesterol, obesity, and low immunity. In fact, organizations such as the World Health Organization (WHO) and the Global Alliance for Improved Nutrition (GAIN) are launching programs worldwide to fortify basic foods in order to address diseases and conditions caused by malnutrition.

Similarly, a growing number of manufacturers are responding to consumer interest by turning to fortification, specifically combining multiple ingredients, to capitalize on scientific advances revealing how certain food components can delay the onset of diseases such as cancer, osteoporosis and diabetes and assist particular demographic groups with ailments and lifestyle issues.  Every day, a diverse array of functional ingredients is used to fortify foods and beverages – one nutrient not often discussed is conjugated linoleic acid (CLA).

CLA refers to a group of 8 isomers that are structurally similar to linoleic acid, which is also known as omega-6. The only structural difference between linoleic acid and the CLA isomers is the location of their two double bonds.  Research is discovering that CLA has a wide range of important biological effects. Studies indicate that it may enhance immunity, protect against cancer and heart disease and help to build muscle and promote fat loss. Recent research suggests that CLA may also help promote healthy glucose and insulin metabolism1.

Ruminants (beef, lamb and veal) used to contain substantial amounts of CLA in their muscle tissue, but switching these animals from pasture land (grass diets) to feedlots where they are primarily fed grain has resulted in approximately a 75% decline in these animals. Since the 1960s, the CLA content of dairy products has declined by about two-thirds. It has been speculated that the dramatic decline in available CLA (in American diets) may be linked to increased rates of cancer, heart disease and the epidemic of obesity and, like a dieter’s dream come true, may help melt body fat and build muscle.

Active forms
The two most active forms of CLA are the cis-9, trans-11 isomer and the trans-10, cis-12 isomer.

Since CLA is a fat-soluble nutrient, CLA supplements will be better absorbed from the gastrointestinal tract if they are taken with meals that contain some fat in the food that is being eaten.

Toxicities & precautions – General
Most studies have reported that conjugated linoleic acid is quite safe. In one toxicity study, the organs of animals given extremely high doses of CLA for 36 weeks did not exhibit any signs or symptoms of toxicity. Based on these results, the authors of this study suggested that CLA should be considered a substance that is generally recognized as safe (GRAS)2. However, studies with humans reported that CLA caused increased levels of lipid peroxidation, which prompted authors to state that further studies on CLA are urgently needed3,4. In addition, one study found CLA adversely affects glucose and insulin levels in those with Type 2 Diabetes5. 

Functions in the body

Antioxidant Defense
According to the discoverer of conjugated linoleic acid, Dr. Michael Pariza, CLA provides a previously unrecognized form of antioxidant defense against membrane attack by oxygen free radicals6. Studies using electron spin resonance (ESR) spectrometry have confirmed that CLA has free radical scavenging attributes whereas its structural cousin linoleic acid (LA) does not7.

Improves Blood Lipids
CLA improves blood lipids by lowering triglycerides and cholesterol levels. Studies in hamsters and rabbits indicate that this slows the onset of atherosclerosis compared to control animals7,8.

Lipid and Insulin Metabolism
CLA seems to help normalize impaired glucose tolerance and improve hyperinsulinemia due to its influence on hormone receptors that regulate genes involved in lipid and insulin metabolism9.

Reductions in Body Fat
Conjugated linoleic acid inhibits the activity of the enzyme lipoprotein lipase. This is an enzyme that breaks down fat particles in the blood so that they can be taken up by fat cells called adipocytes for storage. Thus, CLA helps to prevent the deposition and buildup of fat in the body. In animal studies, CLA resulted in a 66% reduction in lipoprotein lipase activity, which resulted in substantial reductions in body fat coupled with 5% to 14% increases in lean body mass10. Results of a study indicated that CLA reduced body fat mass and increased lean body mass in healthy overweight adults11,12.

Fortifying foods with CLA
With an obesity epidemic sweeping the globe and an increasing the risk of adverse heath outcomes, such as heart disease, diabetes and cancer, there has been increasing interest in determining whether various bioactive food components can influence health ailments. When fortifying new products, there are many challenges we’re faced with every day – factors that impact the stability of nutrients and their retention, such as temperature, moisture, pH and oxygen, bioavailability and interactions.  Realizing this, Fortitech urges product developers to thoroughly investigate nutrient characteristics prior to incorporating them into products. Depending on the type of product, formulators should select proper functional food ingredients making use of synergistic properties and thus, improving the nutritional benefit.

1 Houseknecht KL, Vanden Heuvel JP, Moya-Camarena SY, Portocarrero CP. Dietary CLA normalizes impaired glucose tolerance in the Zucker diabetic fatty fa/fa rat. Biochem Biophys Res Commun. Jun1998;247(3):911.

2 Scimeca JA. Toxicological evaluation of dietary CLA in male Fischer 344 rats. Food Chem Toxicol. May1998;36(5):391-5.

3 Basu S, et al. CLA induces lipid peroxidation in humans. FEBS Lett. Feb 2000;468(1):33-6.

4 Riserus U, Vessby B, Arnlov J, Basu S. Effects of cis-9,trans-11 CLA supplementation on insulin sensitivity, lipid peroxidation, and proinflammatory markers in obese men. Am J Clin Nutr. Aug2004;80(2):279-83.

5 Moloney F, et al. CLA supplementation, insulin sensitivity, and lipoprotein metabolism in patients with type 2 diabetes mellitus. Am J Clin Nutr. 2004 Oct;80(4):887-95.

6 Pariza MW, Ha YL. Conjugated dienoic derivatives of LA: a new class of anticarcinogens. Med Oncol Tumor Pharmacother. 1990;7(2-3):169-171.

7 Yu L. Free radical scavenging properties of CLA. J Agric Food Chem. Jul2001;49(7):3452-6.

8  Nicolosi RJ, et al. Dietary CLA reduces plasma lipoproteins and early aortic atherosclerosis in hypercholesterolemic hamsters. Artery. 1997;22(5):266-77.

9  Lee KN, et al. CLA and atherosclerosis in rabbits. Atherosclerosis. Jul1994;108(1):19-25.

10 Houseknecht KL, et al. Dietary CLA normalizes impaired glucose tolerance in the Zucker diabetic fatty fa/fa rat. Biochem Biophys Res Commun. Mar1998;244(3):678-82.

11 Park Y, et al. Effect of CLA on body composition in mice. Lipids. Aug1997;32(8):853-8.

12 Gaullier JM, Halse J, Hoye K, et al. CLA supplementation for 1y reduces body fat mass in healthy overweight humans. Am J Clin Nutr. Jun2004;79(6):1118-25.

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