Conjugated Linoleic Acid Often Has Mixed Effects in Type 2 Diabetes CME
News Author: Laurie Barclay, MD
CME Author: Charles Vega, MD, FAAFP



Oct. 1, 2004 — Supplementation with conjugated linoleic acid (CLA) has mixed effects in type 2 diabetes mellitus, according to the results of a randomized, double-blind trial published in the October issue of the American Journal of Clinical Nutrition. CLA had an adverse effect on insulin and glucose metabolism while having a beneficial effect on lipids.

"Some animal studies have suggested that CLA supplementation may have therapeutic potential with respect to insulin sensitivity and lipid metabolism, which are important cardiovascular disease (CVD) risk factors associated with type 2 diabetes mellitus," write Fiona Moloney, MD, from the Trinity Centre for Health Sciences in Dublin, Ireland, and colleagues. "There are relatively few human intervention studies, and the results of those few are mixed. Most of the evidence regarding body composition suggests that CLA supplementation does not reduce body weight or body fat or increase fat-free mass in humans."

In this study, 32 subjects with stable, diet-controlled type 2 diabetes received CLA (3.0 g/day; 50:50 blend of cis-9,trans-11 CLA and trans-10,cis-12 CLA) or placebo for eight weeks. Before and after the intervention, subjects had a three-hour 75-g oral glucose-tolerance test, and measurement of fasting plasma lipid concentrations and inflammatory markers.

CLA supplementation increased fasting glucose concentrations by 6.3% (P < .05), and it reduced insulin sensitivity measured by homeostasis model assessment, oral glucose insulin sensitivity, and the insulin sensitivity index (composite; P < .05).

Because of an increase in high-density lipoprotein2 (HDL2 ) cholesterol concentrations in the CLA group (P < .05), total HDL-cholesterol concentrations increased by 8% (P < .05), and the ratio of low-density lipoprotein (LDL) to HDL cholesterol decreased (P < .01). CLA supplementation also reduced fibrinogen concentrations (P < .01) but had no effect on CVD inflammatory markers (C-reactive protein and interleukin 6).

"CLA supplementation had an adverse effect on insulin and glucose metabolism," the authors write. "Whereas CLA had positive effects on HDL metabolism and fibrinogen, a therapeutic nutrient should not be associated with potentially adverse effects on other clinical markers of type 2 diabetes.... Clearly the effect of CLA supplementation is isomer-specific and dependent on the diabetic risk of the experimental model."

The Wellcome Trust, U.K., supported one of the authors. None of the authors have any commercial interest in CLA or any other conflict of interest.

Am J Clin Nutr. 2004;80:887-895

http://www.medscape.com/viewarticle/490444

Maybe this has something to do with the studies that show red meat increases diabetes risk? Beef is rich in CLA after all.

Makes you wonder... it had a beneficial effect on lipids but negative effect on metabolism. Seeing as these two effects are often related, it really is a puzzle isn't it? It makes you realize how impossible it is to truly understand what's healthy and what's not. The more you know the more you realize you don't know.

There's just way too many conflicting studies on CLA at the moment, that concentrating on just one study is quite erroneous.

One says it's bad for IS, next one says it's good. One says it's bad for CVD risk factors, next one says it's good. Etc. etc., the big picture on CLA is still totally messy. Anyone seen a good meta-analysis on current CLA studies yet?

As a side note: considering CLA has probably existed a loooong time (enzymatic creation method, enzymes are shared a long way back "in history", even cross-species sharing is very usual), and that the human body can create one CLA isomer from trans-11 fatty acids, I remain smack dab on the fence, but I have to confess am a bit tilted on the "maybe it has good effects more than bad" side. ESPECIALLY since contrary to the glucose homeostasis question, the cancerous issue re CLA is much less controversial: lots of studies pointing at possible antitumorgenic effects of CLA already exist.

Willett's big Harvard studies didn't show an association between diabetes and red meat per se, either for men or women (2 studies of different aged women). Only processed meat was related.