Conjugated linoleic acid (CLA) consists of a series of positional and geometric dienoic isomers of linoleic acid that occur naturally in foods. That's the technical definition, but in plainspeak, CLA is a fatty acid found mainly in cooked beef that has undergone a minor structural change. But with that change comes a tremendous alteration in its biological properties. You're thinking: Fat is fat. How can it be good for me?" Well, this fat is unlike any other.
For one thing, CLA exhibits antioxidant and anticancer properties Michael Pariza, PhD, who has clone the bulk of existing CLA research, has shown that in laboratory mice with skin lesions and tumors, those treated with CLA had very minor or small lesions compared to untreated mice. In another experiment, Pariza fed rabbits 0.5 gram of CLA per day and found that 12 weeks of treatment reduced low-densitv-lipoprotein ("bad') cholesterol and triglycerides dramatically. The aorta (the large vessel leaving the left ventricle of the heart) of these rabbits was less clogged with plaque than those of the rabbits not fed CLA.
Additionally, CLA has been shown to overcome some of the catabolic effects of endotoxin (a poison contained in a cell) injection in mice. You might ask: "So what? So it helps fight heart disease and cancer heck, I could just eat a bunch of fruit and veggies or load up on Vitamin E. But will it make me workouts better? Will it make me bigger leaner and more muscular?
A study presented at the 1997 National Strength and Conditioning Association conference examined the idea that CLA supplementation might have a similar effect in humans as it does in our four-legged friends producing a leaner, more muscular creature. This time, scientists used resistance-trained men, not rodents, who supplemented daily with either 9 grams of olive oil (a placebo) or CLA (6 grams plus 3.2 grams of fatty acids). After a 28-day supplementation period, no differences were found in the subjects' gross measures such as bodvweight, fat mass or fat-free mass. Researchers did, however, find some interesting data suggesting that a longer supplementation period might have produced statistically significant differences.
An analysis of the subjects' strength showed that the CLA group increased their bench press by 5.5 pounds and their leg press by 30.6 pounds. Though not statistically significant, these changes could be indicative of a trend, in addition, some differences existed in the ratio of blood urea nitrogen to creatinine which, as a marker of anabolic/catabolic status, would suggest a potential net anabolic effect.
Certainly the human study could be criticized for showing no statistically significant differences, which you might say once again proves what a worthless bunch of shit this supplement is. On the other hand (this is the view I'd take), just because the differences weren't statistically significant doesn't mean they weren't physiologically significant. As a real-life example, compare the times of world-class 100-meter sprinters over the course of a season and you'd be hard-pressed to find statistically significant differences (they often vary by only hundredths (if a second). Yet an obvious difference exists. For a bodybuilder, a 1%-2% difference in muscle mass is physiologically huge! Furthermore, the human studies examined a four-week supplementation period, whereas Pariza's animal studies lasted eight weeks, and those particular animal studies did exhibit both physiologically and statistically significant changes in lean body mass and one week for a rat is a much longer period relative to that animal's life span than it is for a human.
If this type of study were carried out for several months on humans, I think it's wholly possible that you'd get demonstrable differences. Perhaps that study is being carried out as you read this. Nonetheless, is it worthwhile to supplement with CLA? Maybe. As mentioned, CLA is found in its highest concentrations in cooked meats such as beef and less so in poultry and eggs. Vegetable fats are a poor source.