Topics discussed: What is CLA, does CLA work, and is CLA safe for prolonged use?

The basics 

Does CLA work? Well, let us first examine what CLA is. Conjugated linoleic acids (CLAs) are a group of naturally occurring polyunsaturated fatty acids. They were first isolated in 1987 by researchers at the University of Wisconsin-Madison who discovered these mysterious fatty acids could inhibit chemically induced cancer in mice.

These fatty acids are naturally produced in the rumen (first stomach) of cattle, buffalo, deer, sheep, and goats. Forage and grass derived fatty acids undergo biohydrogenation by bacteria to give CLAs. The best dietary sources are therefore dairy and meat products from healthy grass fed livestock.

Since the 1987 study, a wave of research has linked CLA to a range of health benefits including reducing breast cancer occurrence, relieving asthma, controlling allergies, controlling blood sugar levels, and inducing fat loss. Sounds promising.

There is a lot of hype around CLA within the fitness industry, some of which is justified. But there are significant adverse effects that for one reason or another are not addressed in other blogs! In this article, we are going to focus on fat loss because this is what CLA is mostly being promoted for.

Isomers

This section is perhaps boring, but relevant to understanding how CLA works. CLA exists in a variety of isomers, in other words, molecules with the same formula but a different spatial arrangement of atoms.  We are starting to understand that different CLA isomers have different effects on our physiology. This is not surprising considering that isomers have varying melting points and oxidative rates. Our objective is to understand the different forms of CLA available to us keep tabs on the research as it comes out.

Studies have found that one specific isomer called t10-c12 can reduce lipogenesis (fat formation) and potentiate lipolysis (breakdown of fatty deposits). Sounds promising. The effects are theorized to be due to the mediation of a group of nuclear receptor proteins called PPARs. These receptor proteins control gene expression for the storage and catabolism of fatty acids. Your genetic predisposition might be to put on weight, but your gene expression can change for the better.

Interestingly, the number of adipocytes (fat storage cells) does not decrease, rather it is their size that is reduced. So these are the finding in animal studies, but does CLA work in human trials?

Animal vs human studies

Animal studies have helped to identify the mechanisms by which CLA may able to reduce fat in humans, however that does not necessarily mean CLA will work for everyone equally. Firstly researchers have found inconsistent effects in different species. For example, rats supplemented with CLA had a smaller but faster reduction of fat tissue compared to mice.

There are few studies that have looked at human trials, but now a picture is emerging. It appears that CLA is able to increase the fat reduction effects of regular exercise over a 12 month period. However how much of the effect is attributed to CLA or exercise is undetermined. Secondly, CLA appears effective for people that are overweight, but for people with body fat in the normal range studies reported no significant reduction.

Initial indications are that CLA may have three distinct health benefits. Improved fat profile, an anti-inflammatory effect that reduces oxidative stress, and improved insulin signalling. Again more studies are required to confirm so we will leave that there for the time being.

A 2011 meta analysis by Onakpoya et al concluded from the evidence to date, that there is a small but statistically significant fat-loss attributed to CLA over placebo. They also said there is not yet sufficient evidence to confirm a clinically relevant effect.

Adverse reactions  

Plot twist. There have been several reports of significant adverse effects. In animal studies, the t10-c12 isomer has been flagged as being potentially carcinogenic, inducing insulin resistance, and increasing the risk of atherosclerosis (fatty deposits within arteries). Sounds bad, however the same studies showed that the 9-CLA isomer reduces the risk of CVD and carcinogenesis (cancer formation). Which arguably goes some way to mitigate the damage of t10-c12.

But the concerns continue to mount up. Studies have repeatedly shown a significant increase in oxidative stress. Currently, one of the most widely accepted theoretical models of the ageing process is oxidative stress induced by free radicals. This happens when our bodies are overwhelmed with destructive reactive oxygen species (ROS) and our bodies are unable to detoxify them, or repair the resulting damage. This is not to be taken lightly since prolonged oxidative stress can lead to cancer and heart disease. The following is a direct quote from a 2015 systematic review by Sailas Benjamin et al:

“Supplementation with 10-CLA dramatically increased the rates of oxidative stress, to levels considerably higher than that observed in heavy smokers”.

Furthermore, other studies have noted that CLA causes insulin resistance. This is a disorder that makes cells unresponsive to insulin, which eventually leads to hypoglycemia (i.e. type 2 diabetes). It gets worse because unutilized plasma insulin can then lead to increased apatite, especially for carbohydrates and sugars. Clearly, this is likely going to counter any marginal fat loss benefit.

Bottom line: Does CLA work?

The short answer is, yes in some cases. You may have noticed that the research to date is very discordant with respect to CLA’s ability to reduce body fat. My interpretation is that there is a small but definite body fat reduction for specific subgroups. CLA, if used at all, should certainly not be relied on in isolation but rather be viewed as one tool in a wider fat-reduction strategy. Remember scientists are trying to isolate the effects of CLA from all the other body fat modifying factors, over a long time-frame. Our goal is very different. Ideally, it would be great to have the marginal effect of CLA nailed down, but our goal does not necessarily require this. Our goal is to reduce as much fat as possible, as soon as possible, and as safely as possible (assuming you are not attempting to bulk).

If your body fat is in the normal range and you are looking to make further cuts, then CLA will probably have little if any effect. If however you are overweight then CLA can have a noticeable effect if taken consistently for over one year. In other words, the small marginal effect will add up. The issue with apatite modification would need to be considered especially if you are on a standard American diet. Satiating your appetite can be achieved with a better balance of fibre, fat, and protein. With that said, asking “does CLA work?” is not the right question:

Should you take CLA? 

Categorically NO. Ultimately the findings on oxidative stress and insulin resistance make CLA supplementation a crazy idea. Indeed the overwhelming consensus from researchers is that CLA cannot be recommended. Accelerating one of the major ageing processes while increasing the risk of cancer is not worth a non-guaranteed marginal effect on body fat. Perhaps in future when we better understand the specific effects of each isomer on human subgroups (age, gender, race) and we have clinically proven ways to mitigate the adverse effects, then CLA may be viable.

A final thought on irresponsible bloggers

Rarely do I talk about other bloggers unless I think they have something positive and insightful to reference. However in the case of CLA, I have been surprised by the number of bloggers advocating its benefits while whitewashing its adverse effects. The blatant misrepresentation of the evidence to promote sales of a controversial product like this does a real disservice to the fitness community. We are all in the same boat, trying to improve ourselves and share knowledge. I won’t mention names but they are ranking at the top of Google and promoting CLA. I hope that in time these big influencers will be forced by readers to write less bent content.

Does CLA work? Well be careful who you ask and get lots of opinions!

Further Reading

Pros and cons of CLA consumption: an insight from clinical evidence; Sailas Benjamin et al, Nutr Metab (Lond). 2015

A Diet Rich in Conjugated Linoleic Acid and Butter Increases Lipid Peroxidation but Does Not Affect Atherosclerotic, Inflammatory, or Diabetic Risk Markers in Healthy Young Men; Marianne Raff et al, 2008 American Society for Nutrition

A review on effects of conjugated linoleic fatty acid (CLA) upon body composition and energetic metabolism; Tatiana Ederich Lehnen et al, J Int Soc Sports Nutr 2015

Treatment with dietary trans10cis12 conjugated linoleic acid causes isomer-specific insulin resistance in obese men with the metabolic syndrome; Risérus U, Diabetes Care. 2002 Sep;25(9)

Opposing effects of cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acid on blood lipids in healthy humans; Tricon S et al, Am J Clin Nutr. 2004 Sep;80(3)

Supplementation with conjugated linoleic acid causes isomer-dependent oxidative stress and elevated C-reactive protein: a potential link to fatty acid-induced insulin resistance; Risérus U, Circulation. 2002 Oct 8;106(15)

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