CLA may be a cure-all for the rodent population, but does it actually work for humans?

CLA may be a cure-all for the rodent population, but does it actually work for humans?
by Dr. Jarret Morrow

Conjugated linoleic acid (CLA) refers to a mixture of isomers of linoleic acid which is found naturally in animal products of ruminant (any of the hoofed animals) sources including meat and diary products. Though CLA is a trans fat, many researchers claim that unlike other trans fatty acids, it is not actually harmful. Further, recent interest in CLA stems from several well-document properties which have been researched in rodents including: antiobesity, antiatherogenic, antidiabetic, and anticarcinogenic properties. If you’re a rodent with diabetes, clogged arteries, cancer, or obesity, then CLA supplementation seems like a pretty good idea. However, though CLA exhibits these properties in rodent models, what effect does it actually have on humans?

Of the various purported reasons for people consuming supplements containing CLA isomers, perhaps the most common reason is for weight loss. In mice, CLA supplementation has resulted in dramatic decreases in adipose mass, with as much as 50% reduction in mice fed these isomers. However, in human studies, the results of CLA supplementation on body composition have been far less definitive. Initial studies have found conflicting results on CLA supplementation’s effect on reducing body fat mass and increasing muscle mass (Larsen et al, 2006). However, several recent studies support CLA supplementation’s efficacy in reducing body fat in obese adults. Three of the most recent randomized, double-blind, placebo controlled trials support CLA supplementation’s efficacy in reducing body fat mass in healthy, overweight adults (Watras et al, 2007; Gaullier et al al, 2007; Gaullier et al, 2005). In addition, a recent randomized controlled trial found that CLA may also increase lean body mass in obese humans (Steck et al, 2007). Overall, there is reasonably compelling evidence that CLA supplementation may help you increase your lean body mass as well as reduce body fat.

Though CLA has been shown to have beneficial effects on cardiovascular health in some animal models, the evidence to support these benefits in human models is currently lacking (Badinga et al, 2006). Even within animal models, there is some evidence that CLA reduces atherogenesis in rabbit and hamster models, but not in rat or pig models (Badinga et al, 2006). Not only is the evidence lacking to support any beneficial effects on the human cardiovascular system, but some recent evidence suggests that CLA may actually decrease HDL levels (good cholesterol) and increase markers of inflammation in the short term (Steck et al, 2007). It is uncertain whether or not these serum changes are clinically significant. Current scientific literature does not currently support the rodent studies which suggest that CLA will improve your cardiovascular health.

Antidiabetic properties of CLA have been exhibited in animal models including rat models. Additionally, a recent study (Colakoglu et al, 2006), demonstrated that CLA supplementation did, in fact, have a beneficial effect on serum glucose levels and insulin concentrations. However, in obese men with metabolic syndrome, CLA may worsen insulin resistance (Riserus et al, 2002). For people who have diabetes, current research suggests that they use CLA with caution and only under the advice of their physician.

In terms of carcinogenesis, though CLA supplementation has shown numerous potent anticarcinogenic properties in cancer models, the evidence is currently inconclusive and may be species dependent. To date, there have been no definitive clinical trials which have demonstrated anticarcinogenic properties in any human clinical trials. Though the anticarcinogenic properties of CLA are exciting, there is no current evidence to support the use of CLA supplementation in patients who suffer from cancer.

To summarize, the putative benefits of CLA supplementation include: anticarcinogenic, antidiabetic, antiathrogenic, and antiobesity effects. The scientific evidence for all but the antiobesity effect is currently inconclusive and likely species dependent. Recently, randomized clinical trials have demonstrated decreases in body fat mass and increases in lean body mass in obese adult populations. However, the change in body composition demonstrated in human models, is far less than studies have demonstrated in animal models. If you are considering CLA supplementation for its potential cardiovascular, antidiabetic, or anticarcinogenic effects, current scientific evidence does not support its use for these conditions. However, if you are an obese adult considering CLA supplementation to support health weight loss along with a diet and exercise program, it may be worth considering.

1. Colakoglu S, Colakoglu M, Taneli F, Cetinoz F, Turkmen M. Cumulative effects of conjugated linoleic acid and exercise on endurance development, body composition, serum leptin and insulin levels. J Sports Med Phys Fitness. 2006 Dec;46(4):570-7
2. Gaullier JM, Halse J, Hivik HO, Hye K, Syvertsen C, Nurminiemi M, Hassfeld C, Einerhand A, O’Shea M, Gudmundsen O. Six months supplementation with conjugated linoleic acid induces regional-specific fat mass decreases in overweight and obese. Br J Nutr. 2007 Mar;97(3):550-60
3. Steck SE, Chalecki AM, Miller P, Conway J, Austin GL, Hardin JW, Albright CD, Thuillier P. Conjugated linoleic acid supplementation for twelve weeks increases lean body mass in obese humans. J Nutr. 2007 May;137(5):1188-93.
4. Watras AC, Buchholz AC, Close RN, Zhang Z, Schoeller DA.The role of conjugated linoleic acid in reducing body fat and preventing holiday weight gain. Int J Obes (Lond). 2007 Mar;31(3):481-7. Epub 2006 Aug 22
5. Larsen TM, Toubro S, Gudmundsen O, Astrup A. Conjugated linoleic acid supplementation for 1 y does not prevent weight or body fat regain. Am J Clin Nutr. 2006 Mar;83(3):606-12.
6. Gaullier JM, Halse J, Hye K, Kristiansen K, Fagertun H, Vik H, Gudmundsen O. Supplementation with conjugated linoleic acid for 24 months is well tolerated by and reduces body fat mass in healthy, overweight humans. J Nutr. 2005 Apr;135(4):778-84
7. Badinga L, Greene ES. Physiological properties of conjugated linoleic acid and implications for human health. Nutr Clin Pract. 2006 Aug;21(4):367-73.
8. Riserus U, Arner P, Brismar K, Vessby B. Treatment with dietary trans10, cis12 conjugated linoleic acid causes isomer-specific insulin resistance in obese men with the metabolic syndrome. Diabetes care. 2002;25:1516-1521.

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