Conjugated linoleic acid (CLA) is a naturally occurring trans fatty acid of at least 28 isomers of linoleic acid found mostly in the meat and dairy products derived from ruminants. It is conjugated because the double bonds in this fatty acid alternate at one point. CLA can be either cis or trans-fats.
After looking around online I found that there are several proposed benefits of conjugated linoleic acid: 1) Increased metabolic rate, 2) enhanced muscle growth, 3) lowering of cholesterol and triglycerides, 4) lowering of insulin resistance, 5) reduction of food-induced allergic reactions and 6) enhanced immune system.
You should always be wary of an article that is talking about a supplement and trying to sell it at the same time. The above mentioned claims comes from a "researcher" that wrote on article on bodybuilding.com where the product is sold to the public. The article definitely touts it as something necessary to have in your supplement pill box. Bodybuilding.com paid the researcher for his work which includes citations.
I have reviewed this product in the past for a cousin of mine that was told she should take it. I did some preliminary research and found that it actually increases cholesterol and does little for lean body mass gains.
I'm now, researching it a second time more thoroughly for my website. I'm going to look at the primary literature (the most evidence based studies) to see what has been discovered about it. Already, I suspect that most of the benefits where shown in animal models with little done in humans to show benefit. One must be careful with animals because what works in animals does not always work in a living human. Our DNA has enough differences for this to occur.
In one study, CLA has been found to have an anti-carcinogenic effect by reducing VEGF and bFGF serum levels and by blocking flk-1 receptors, thereby inhibiting vascular growth critical to tumor growth and survival. The study also shows that CLA administration significantly reduces angiogenesis (new blood vessel formation) in the cerebellum; however, this discovery is limited to animals. By preventing new blood vessel formation in the brain, a tumor cannot receive nourishment without the new blood vessel feeding it. This suggests that it may have a therapeutic treatment for cancer in humans but it is not certain.
In another, study, a meta-analysis said that CLA results in humans have been inconsistent. In this analysis it was found that 3.2 grams of CLA a day produced 0.198 lb loss in body fat per week plus or minus 0.08kg/wk, a significant finding.
In a study from the International Journal Of Obesity (London) holiday weight gain was looked at with CLA. It was found that those on placebo instead of CLA showed a greater rate of weight gain, indicating CLA prevented some weight gain over the holidays. It was found over the study duration of six months that body fat was significantly reduced in the CLA group which reported a loss of 1.0 kg plus or minus 2.2 kg. This was significant.
CLA had no affect on insulin resistance, blood lipids and markers of liver function or markers of inflammation. Note: there was no change in insulin resistance and blood lipids which are two claims that marketers are putting forward as purposed benefits of CLA.
A study from the American Journal of Clinical Nutrition found after 101 patients lost weight, 51 of them were put on CLA 3.4 grams a day and 50 of them were put on olive oil. After a total of one year, both groups the CLA group and the olive oil group regained all the fat mass they had lost initially to qualify for the study. This shows that CLA not only didn't cause them to loss any additional weight, it also didn't prevent them from gaining back the weight they lost. This is an important study because it tested CLA over a long period of time and also because it used a relatively good amount of patients in the test (a total of 101). The more patients used, the stronger the evidence of the results. This is in contrast to the previous study which looked at 40 total subjects, 20 taking CLA and 20 taking placebo. In this study there was a siginificant increase in the number of leukocyhtes observed with CLA supplementation. Leukocytes are white blood cells of your immune system. This finding does support the claim that CLA enhances the immune system.
From a study in the Journal of Diabetes Metabolic Disorders, showed that CLA administration for 8 weeks among 19 patients showed there was no affect on any indicators of metabolic control in overweight type 2 diabetic patients. That means there was no change in body mass, fat mass, lipids, insulin resistance, blood pressure and any other metabolic constituents. This study was only for 8 weeks and was done with very few patients, a weak study that shows it is ineffective but it is again the second study to show no effects on lipids or insulin which are purported benefits.
A norwegian study summarizes: even though CLA in rodents reduces fat mass and increases muscle mass, the results from 13 randomized, placebo controlled trials does not support these findings with regard to humans. In fact, one isomer, the 10-trans, 12-cis may have a negative effect on carbohydrate and lipid metabolism by inducing insulin resistance and hyperlipidaemia.
This supports what I found out earlier for my cousin when I found that it increases your bad cholesterol (LDL) while lowering your good cholesterol (HDL). Further, they say the fat reducing effect of CLA in is through PPARgamma, which is humans may cause adverse metabolic effects such as increases in cholesterol.
The cholesterol finding is settled. It was found that the 10-trans and 12 cis isomer increases LDL and decreases HDL as found earlier but the 9-cis, 11-trans increases HDL and decreases LDL. This supports the claim that CLA can indeed lower cholesterol levels. The study was done over a period of 8 weeks which is short. If you're going to take CLA you definitely want to stay away from the 10-trans, 12-cis isomer.
The seventh study I looked at, explains that CLA does indeed reduce weight gain and fat deposition in rodents but in humans it produces less significant and inconsistent effects on body weight and composition. The study also states that the 10-trans, 12-cis isomer in humans is the one that has produced marignal results with fat loss in humans. Remember, this is also the isomer that two studies confirmed increases your bad cholesterol. More cholesterol means more cardiovascular adverse events such as heart attacks. Is the risk of heart attacks worth a "marginal" loss in body fat?
In a study form the European Journal of Clinical Nutrition, CLA with a mixture of isomers both 10-trans, 12-cis and 9-cis, 11-trans was consumed. The study took place after a the study participants had lost weight. What was studied was their regaining of weight such as in an earlier study we looked at. It was found that the consumption of 1.8 or 3.6 grams of CLA/day, mixed isomers results in a decrease in appetite (hunger, satiety and fullness) and was dose dependent; however, there was no less weight regain in the group taking CLA than placebo despite reductions in hunger. This study was 13 weeks in duration.
Well, I presented mostly human based studies about CLA. I searched amazon and it is a very popular dietary supplement at the moment, looks like tons of people are taking it. There was definitely some support of the claims but there was no ground-breaking, extremely convincing evidence that it causes weight loss, in fact it seems that all the researchers are hesitant to say it significantly improves weight loss. When you purchase the product you also don't get to single out either isomer. You are likely buy a mixture of both isomers which means you are getting some of the 1-trans, 12-cis which was shown to increase cholesterol but you are also getting some of the other which may decrease cholesterol (I didn't see an article proving this).
It is reasonably priced at about $20.00 for a 50 day supply and that's at the recommended 3.6 grams per day. I'll offer it here incase you are interested in taking it, you'll never know exactly what it does unless you try it. If you try it I recommend getting your cholesterol checked when you start it and then 2 months after you've been on it to see if there is any change. You also may want to get some sort of body composition test done to see if you are gaining lean body mass and losing your fat mass. To order click here or below on the picture of the most popular CLA supplement on amazon.
1. Sikorski AM, Hebert N, Swain RA. Conjugated Linoleic Acid (CLA) inhibits new vessel growth in the mammalian brain. Brain Res. 2008;1213:35-40.
2. Whigham LD, Watras AC, SChoeller DA. Efficacy of conjugated linoleic acid for reducing fat mass: a meta-analysis in humans. Am J Clin Nutr. 2007;85(5):1203-11.
3. Watras AC, Buchholz AC, Close RN, et al. The role of conjugated linoleic acid in reducing body fat and preventing holiday weight gain. Int J Obes (Lond) 2007;31(3):481-7.
4. Larsen TM, Toubro S, Gudmundsen O, et al. Conjugated linoleic acid supplementation for 1 y does not prevent weight or body fat regain. Am J Clin Nutr. 2006; 83(3):606-12.
5. Haugen M, Alexander J. Can linoleic acids in conjugated CLA products reduce overweight problems? Tidsskr Nor Laegeforen. 2004;124(23):3051-4.
6. Tricon S, Burdge GC, Kew S. Opposing effects of cis-9, trans-11 and trans-10, cis-12 conjugated linoleic acid on blood lipids in healthy humans. Am J Clin Nutr. 2004;80(3):614-20.
7. Wang YW, Jones PJ. Conjugated linoleic acid and obesity control: efficacy and mechanisms. Int J Obes Relat Metab Disord. 2004; 28(8):941-55.