While I was looking at something unrelated (except that it was a fatty acid), the following popped up in my search: Weight loss supplement - conjugated linoleic acid - shows nasty side effects. Conjugated linoleic acid (CLA) first came to my attention, other than hearing about it as a supplement from time to time, during a discussion on trans fats and trans fat content of certain foods. CLA is a trans fat, it's just not an unnatural nasty chemical we associate with the term these days. It's found in meat of grassfed animals in particular, milk/dairy from same animals and eggs. If you do a search on CLA and trans fat you'll turn up all manner of reports how it's the "good" or "healthy" trans fat. In addition to some anti-cancer claims, it's also touted as the "belly busting" trans fat. Sign me up!
But, not so fast according to the article, which references two studies: (2007, nothing new here, just thought I'd pass this along as I hear buzz over CLA from time to time)
- In mice, CLA supplementation caused rapid weight loss, but excessive hepatic fat accumulation and the mice became insulin resistant.
- In rats, CLA supplementation did not cause whole body fat loss, but decreased hepatic fat content and the rats became more insulin sensitive.
“Many people take conjugated linoleic acid as a supplement in hopes of trimming body fat, and it seems to work,” Belury said. “But we're not sure what else it does to the body. Studying conjugated linoleic acid's effects in two different animal models may help us to better understand any additional effects in humans.
“It seems that these mice and rats represent a continuum of possible side effects induced by conjugated linoleic acid,” she continued. “The question is, are humans more like mice or rats? We're probably somewhere in between.”
Leaving aside whether rats or mice or neither is a good animal model to predict the human effects of CLA, one thing these two studies demonstrated was that hepatic fat accumulation/loss and body fat accumulation/loss are not always in the same direction. By that I mean we see both hepatic fat accumulation with rapid weight loss, and hepatic fat loss despite no weight loss. (Not sure if hepatic fat loss in the context of weight gain is possible though, that seems unlikely).
Speaking of the mouse, however, the low carbers intent on championing some metabolic advantage that allows them to eat thousands of calories more and lose weight like no tomorrow love this rodent. Remember Mighty Metabolism Mouse? I've also blogged on Hepatic steatosis, inflammation, and ER stress in mice maintained long term on a very low-carbohydrate ketogenic diet. The first study is legendary in low carb circles as the mice eat just as much and either don't gain as much weight or lose weight. But this metabolism comes at the cost of profound liver damage.
So let me be clear that there's much more on this topic that I'm not really all that interested in pursuing at this time(too much I'm more interested in at the moment), but here's one human study that caught my eye: Conjugated Linoleic Acid Impairs Endothelial Function.
To determine the effect of dietary supplementation with conjugated linoleic acid (CLA) on body mass index (BMI), body fat distribution, endothelial function, and markers of cardiovascular risk.
Forty healthy volunteers with BMI >27 kg/m2 were randomized to receive a CLA isomeric mixture or olive oil in a 12-week double-blind study. Subcutaneous body fat and abdominal/hepatic fat content were assessed using skin-fold thicknesses and computed tomography scanning, respectively. Endothelial function was assessed by brachial artery flow-mediated dilatation (FMD). Plasma isoprostanes were measured as an index of oxidative stress. CLA supplementation did not result in a significant change in BMI index or total body fat. There was a significant decrease in limb (−7.8 mm, P<0.001), but not torso skin-fold thicknesses or abdominal or liver fat content. Brachial artery FMD declined (−1.3%, P=0.013), and plasma F2-isoprostanes increased (+91pg/mL, P=0.042).
A CLA isomeric mixture had at most modest effects on adiposity and worsened endothelial function. On the basis of these results, the use of the isomeric mixture of CLA as an aid to weight loss cannot be recommended.
The F2-isoprostanes are "a lipid peroxidation product generally considered to be a marker of increased oxidative stress"
Where I'd be concerned is that if CLA worked for me to lose weight like gangbusters, would that make me more mouse like and be counterproductive to health. If it didn't work for weight loss per se, maybe it's doing a lot of good! Quite a conundrum.