CLA For Weight Loss: Safe, but Ineffective. Conjugated Linolic Acid Fails to Improve Body Composition or Lipid Profile in 8-Week Human Study

The early 2000s were the fat years: "Want to lose fat? Eat fat!" became the credo of more and more nutritional gurus, who put their faithful clients "on" EFAs, PUFAs and a certain fatty acid (FA) that, despite, or rather due to its presence in our food chain, had hitherto received little attention by the medical orthodoxy: conjugated linoleic acid (CLA). All of a sudden, this "unhealthy" trans-fatty acid that can be found in relatively large amounts in high fat milk products, was supposed to become the magic bullet in every dieter's fight against unhealthy or unaesthetic body fat.
So, is the majority of the Americans in the 21st century going to be obese, simply because they are not consuming enough CLA? A recent study from Canadian scientists (Jones. 2011) suggests otherwise.

In a 3-phase crossover trial, Jones et al. recruited 27 overweight (BMI ≥ 25 kg/m²), borderline hypercholesterolemic [LDL-cholesterol (C) ≥ 2.5 mmol/L] men aged 18–60 y, who consumed during three consecutive 8-wk phases (with a 4-wk washout period between each trial) either 3.5 g/d of safflower oil (control) or a 50:50 mixture of trans 10, cis 12 and cis 9, trans 11 (c9, t11) CLA:Clarinol G-80, and c9, t11 isomer:c9, t11 CLA.

Figure 1: Chemical structure of the 2 isomers of conjugated linoleic acid (CLA)
and the unconjugated form linoleic acid (LA)
(image from Kent. 2007)

Body weight, body fat, and lean body mass (all reliably measured by DXA), CLA's effects on fatty acid oxidation, as well as blood lipid profiles and safety biomarkers, including insulin sensitivity, blood concentrations of adiponectin, and inflammatory markers (high sensitive-C-reactive protein, TNFα, and IL-6) and oxidized-LDL were assessed at the beginning and end of each trial. The results were unimpressive:

Compared with the control treatment, the CLA treatments did not affect changes in body weight, body composition, or blood lipids. In addition, CLA did not affect the β-oxidation rate of fatty acids or induce significant alterations in the safety markers tested.

Or, in other words, CLA supplementation @ 3.5g/day did not produce any of the favorable effects potential customers are promised by the advertisements of an industry that thrives on the hopes of overweight of millions of obese individuals world-wide.

A conclusive evaluation of both the effectiveness, as well as the safety of CLA would require further studies using and comparing the effects of different  mixtures of the different CLA isomers that  have been found to exert very different metabolic effects - with the trans-10, cis-12 isomer having a more pronounced effect on PPAR-gamma induced metabolic changes (Hermann. 2009) and more compelling evidence of possible negative side effects, such as increased oxidative stress (Risérus. 2007).

So, after all. The verdict on CLA is still out there! And you know: The SuppVersity is the place, where you will hear about future research first.