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conjugated linoleic acid

What Is It?
Health Benefits
Forms
Dosage Information
Guidelines for Use
General Interaction
Possible Side Effects
Cautions
References

Evidence Based Rating Scale

What Is It? 

Conjugated linoleic acid (CLA) is a slightly altered form of linoleic acid (LA), an omega-6 fatty acid important to human health for various biological processes. Omega-6 fatty acids are derived from the foods we eat (primarily from meats and dairy products). CLA is also available in concentrated dietary supplement form. The optimum dietary intake of CLA has not been established; the average American ingests 150-200 mg of CLA a day. (1-2)

Health Benefits

Numerous claims abound for CLA supplements, including assertions that they can help burn Fat, build muscle, and fight cancer. Although there has been promising research done over the past few decades, it has primarily been in small animals. In some studies, rodents fed CLA-supplemented diets experienced a reduction in accumulated body fat and an increase in muscle mass. (3) Some even experienced a reduction in tumors. (4)

Animal studies have reported beneficial effects of CLA on atherosclerosis, or hardening of the arteries from fatty cholesterol plaques. If a blood clot forms on the surface of a plaque, it can block blood flow resulting in a heart attack. A 2010 human study observed the association between heart attack risk and CLA in dairy products made from the milk of pasture-grazed dairy cows. Dairy products are the main source of dietary CLA and pasture-grazed cows have more CLA in their milk than grain-fed cows. Of the 3626 participants in the study, 1813 had experienced one non-fatal heart attack while the other 1813 had never experienced an attack. At the end of the study, CLA in adipose tissue was associated with a lower risk of heart attack and may offset the adverse effects of the saturated fats found in dairy products. (5) However, CLA does not appear to affect atherosclerosis in humans. In a small study of 401 patients with a BMI above 25, a CLA supplementation of 4 grams per day provided no protection against atherosclerosis. (6)

Specifically, CLA may help to:

Inhibit the growth of some cancers and prevent others. Bovine and mouse animal studies suggested CLA inhibited the expression of the gene required for fatty acid synthesis in normal and malignant breast cells, potentially retarding their growth. In a laboratory study, exposure of human breast cancer cells and malignant fat cells to CLA reduced gene expression and fatty acid synthesis in both cell lines and inhibited cell growth. (7) These findings provide a rationale for designing human studies of CLA's effect on cell growth in patients with breast cancer. Results are mixed for CLA's preventive effect on breast cancer. In 1987 researchers began a large study known as the Swedish Mammography Cohort. Over the course of three years, 61,433 cancer-free women completed a food-frequency questionnaire from which CLA intakes were estimated. Breast cancer incidences were ascertained during an average follow-up of 17.4 years. Study results provided no evidence of a protective effect of CLA on breast cancer. (8) However, a 2010 laboratory study suggested CLA and the omega-3 fatty acids DHA and EPA reduced breast cancer initiating cells. (9)

Animal studies indicate CLA may prevent colon cancer. In one study, rats were fed a 10% beef tallow diet, which increases the risk of colon cancer with long-term use. Some rats were supplemented with CLA. The results indicated that CLA suppressed the formation of colon cancer. (10)

In a human study, 60,708 women from the Swedish Mammography Cohort were assessed for their dietary intake of high-fat dairy products and CLA. The study found that each increment of two servings per day of high-fat dairy food corresponded with a 13% reduction in the risk of colorectal cancer suggesting that high-fat dairy foods and CLA may reduce the risk of colorectal cancer. (11)

Assist with weight management. Numerous animal studies indicate CLA reduces body fat and may increase lean muscle mass. (12) Studies in humans, however, yield conflicting results. In one small study, 62 children aged 6-10 who were overweight or obese received either 3 grams per day of CLA or placebo for six months. At the end of the study, the children who received CLA had a lower increase in Body Mass Index (BMI) compared to the placebo group. Neither group showed a change in glucose, insulin or LDL ("bad") cholesterol levels; however, the CLA group had decreased levels of HDL ("good") cholesterol levels. Longer and larger studies are needed to determine the safety and efficacy of CLA supplementation in children. (13)

A small study of 27 men aged 18-60 with BMI's of 25 or above generated different results. During three 8-week phases, the men consumed either 3.5 grams per day of safflower oil control or CLA. The results indicated CLA had neither a positive or negative effect on body weight, body composition, or cholesterol levels. (14)

Another study compared the effects of CLA and safflower oil on body weight and composition in obese postmenopausal women with type 2 diabetes. In this 36-week study, 55 women received 8 grams per day of either safflower oil or CLA during two 16-week periods separated by a 4-week washout period. At the end of the study, CLA reduced BMI and total adipose mass without altering lean mass. The BMI-lowering effect of CLA was seen during the last eight weeks of both 16-week phases. Safflower oil did not affect BMI or total fat mass but reduced trunk adipose mass, increased lean mass, and reduced fasting glucose. (15)

Forms

  • capsule
  • oil
  • softgel

Dosage Information

The primary sources of CLA are dairy products and beef fat. CLA concentrations in dairy products range from 2.9 to 8.9 milligrams CLA per gram of fat. CLA concentrations in cheeses range from 3.6 to 8.0 milligrams CLA per gram of fat. Blue, brie, edam, and Swiss cheeses have the highest CLA concentrations. (1)

  • For prevention of colorectal cancer: Two servings per day of high-fat dairy products reduced the risk of colorectal cancer by 13%. (11)

  • For weight management: Eight grams per day reduced BMI and total adipose mass in obese postmenopausal women with type 2 diabetes. (15)

Guidelines for Use

No optimum dietary intake for CLA has been established.

General Interaction

  • CLA appears to reduce total LDL and HDL cholesterol levels and may interfere with lab tests. (16)

  • Some evidence suggests CLA may increase vitamin A storage in liver and breast tissue. (17)

  • One form of CLA seems to increase insulin resistance and glucose levels in people with diabetes and affects insulin processing and may increase insulin resistance in men with abdominal obesity and metabolic syndrome. (18)

Possible Side Effects

The most common side effects of CLA are gastrointestinal upset including diarrhea, nausea, and digestion difficulties. (19-20)

Cautions 

Anyone interested in taking CLA supplements should consult a doctor. 

References 

1. Kelly GS. Conjugated linoleic acid: a review. Altern Med Rev. 2001 Aug;6(4):367-82.
2. Daley CA, Abbott A, Doyle PS, Nader GA, Larson S. A review of fatty acid profiles and antioxidant content in grass-fed and grain-fed beef. Nutr J. 2010 Mar 10;9:10.
3. Haugen M, Alexander J. [Can linoleic acids in conjugated CLA products reduce overweight problems?] Tidsskr Nor Laegeforen. 2004 Dec 2;124(23):3051-4.
4. Hubbard NE, Lim D, Erickson KL. Beef tallow increases the potency of conjugated linoleic acid in the reduction of mouse mammary tumor metastasis. J Nutr. 2006 Jan;136(1):88-93.
5. Smit LA, Baylin A, Campos H. Conjugated linoleic acid in adipose tissue and risk of myocardial infarction. Am J Clin Nutr. 2010 Jul;92(1):34-40.
6. Sluijs I, Plantinga Y, de Roos B, Mennen LI, Bots ML. Dietary supplementation with cis-9,trans-11 conjugated linoleic acid and aortic stiffness in overweight and obese adults. Am J Clin Nutr. 2010 Jan;91(1):175-83.
7. Donnelly C, Olsen AM, Lewis LD, Eisenberg BL, Eastman A, Kinlaw WB. Conjugated linoleic acid (CLA) inhibits expression of the Spot 14 (THRSP) and fatty acid synthase genes and impairs the growth of human breast cancer and liposarcoma cells. Nutr Cancer. 2009;61(1):114-22.
8. Larsson SC, Bergkvist L, Wolk A. Conjugated linoleic acid intake and breast cancer risk in a prospective cohort of Swedish women. Am J Clin Nutr. 2009 Sep;90(3):556-60.
9. Erickson KL, Hubbard NE. Fatty acids and breast cancer: the role of stem cells. Prostaglandins Leukot Essent Fatty Acids. 2010 Apr-Jun;82(4-6):237-41.
10. Shiraishi R, Iwakiri R, Fujise T, Kuroki T, Kakimoto T, Takashima T, Sakata Y, Tsunada S, Nakashima Y, Yanagita T, Fujimoto K. Conjugated linoleic acid suppresses colon carcinogenesis in azoxymethane-pretreated rats with long-term feeding of diet containing beef tallow. J Gastroenterol. 2010 Jun;45(6):625-35.
11. Larsson SC, Bergkvist L, Wolk A. High-fat dairy food and conjugated linoleic acid intakes in relation to colorectal cancer incidence in the Swedish Mammography Cohort. Am J Clin Nutr 2005;82:894-900.
12. Kennedy A, Martinez K, Schmidt S, Mandrup S, LaPoint K, McIntosh M. Antiobesity mechanisms of action of conjugated linoleic acid. J Nutr Biochem. 2010 Mar;21(3):171-9.
13. Racine NM, Watras AC, Carrel AL, Allen DB, McVean JJ, Clark RR, O'Brien AR, O'Shea M, Scott CE, Schoeller DA. Effect of conjugated linoleic acid on body fat accretion in overweight or obese children. Am J Clin Nutr. 2010 May;91(5):1157-64.
14. Joseph SV, Jacques H, Plourde M, Mitchell PL, McLeod RS, Jones PJ. Conjugated Linoleic Acid Supplementation for 8 Weeks Does Not Affect Body Composition, Lipid Profile, or Safety Biomarkers in Overweight, Hyperlipidemic Men. J Nutr. 2011 May 18. [Epub ahead of print]
15. Norris LE, Collene AL, Asp ML, Hsu JC, Liu LF, Richardson JR, Li D, Bell D, Osei K, Jackson RD, Belury MA. Comparison of dietary conjugated linoleic acid with safflower oil on body composition in obese postmenopausal women with type 2 diabetes mellitus. Am J Clin Nutr. 2009 Sep;90(3):468-76.
16. 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.
17. Banni S, Angioni E, Casu V, et al. An increase in vitamin A status by the feeding of conjugated linoleic acid. Nutr Cancer 1999;33:53-7.
18. Riserus U, Arner P, Brismar K, Vessby B. Treatment with dietary trans10cis12 conjugated linoleic acid causes isomer-specific insulin resistance in obese men with the metabolic syndrome. Diabetes Care 2002;25:1516-21.
19. 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.
20. 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.

Evidence Based Rating Scale

The Evidence Based Rating Scale is a tool that helps consumers translate the findings of medical research studies and what our clinical advisors have found to be efficacious in their personal practice into a visual and easy to interpret format. This tool is meant to simplify the information on supplements and therapies that demonstrate promise in the treatment of certain conditions.

 

Condition

Rating

Explanation

 

Cancer

   

Animal and human laboratory studies indicate CLA inhibits growth of breast cancer cells; human studies provide mixed results for protective effect on risk of breast cancer. Animal and human studies suggest CLA may prevent colorectal cancer. (7-11)

Obesity  
Study results are conflicting with some indicating decrease in BMI and body fat while others indicate no effect on either. (13-15)

 


Date Published: 04/18/2005
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