So, I'm going to first provide a bit of background about this product and then cover a study that was just published yesterday assessing the effects of CLA during a resistance training program, since only 2 have been done in this specific area.
Conjugated Linoleic Acid
Conjugated linoleic acid is a supplement that has been proposed to increase metabolic rate, increase fat utilization, and thus, with these combined, result in weight loss. CLA is found primarily in dairy products (but not in skimmed dairy products) and meat, specifically beef and lamb.
The typical dietary intake is around 212 mg/day for men and 151 mg/day for women and supplements typically provide 3-5 g/day (so about 20-40 times the intake via the diet).
Although CLA is a relatively popular fat loss aid, the research supporting this product is rather limited. In fact, about half the studies show it is effective and half show the opposite. If you're a rat, cow, or pig (literally, not just what some people may think of you), it is likely very effective; however, it's the human research that doesn't show much promise.
However, what's interesting, at least in my nerdy science mind, is that there are different forms of CLA, called isomers. CLA is a group of positional and geometric isomers, meaning that they are positioned differently, as if putting them in front of a mirror of a fatty acid known as linoleic acid. And it appears that some of these isomers may act different or produce different end results.
So, let's take a look at this study that was published in the February 2006 issue of Medicine and Science in Sports and Exercise - geez, any more current and you would have to do the study yourself!
Medicine and Science in Sports and Exercise,
Vol 38 (2), pp 339-348, 2006
The largest study in humans to date was 1 year long, and it showed that 1 year of CLA supplementation reduced body fat mass in overweight subjects and increased lean tissue mass by small amounts. Two other studies combined CLA with training and one showed it to be effective with regards to reducing body fat and the other showing no change at all with regards to body composition.
So, basically, we're at square one regarding training and CLA. Moreover, it's important to note that the type of training was not even specified in these particular studies, meaning training could mean powerlifting or ballet dancing, for all we know.
Basically this screams that well-conducted studies need to be done to determine the true effects of CLA when combined with an exercise regimen. This was the purpose of this study - determine the effects of CLA supplementation during resistance training.
The authors hypothesized that CLA, when combined with resistance training, would enhance increases in lean tissue mass and strength, reduce fat mass, increase resting metabolic rate, increase fat oxidation, and reduce urinary markers of bone and muscle protein degradation, compared with resistance training alone.
- Body weight
- Percent body fat
- Lean body mass
- Fat mass
- Peak torque for knee extension
- Muscle thickness
- Resting metabolic rate
- Respiratory exchange ratio
- And some other more technical variables that are outside the scope of this article.
Eighty five healthy men and women, 18-45 years of age, were included in this double blind, placebo controlled study. All subjects were currently active, which is important, as "newbies" tend to see much greater results in the beginning.
This was a 7-week study that included a periodized resistance training program that all subjects followed. There were a handful of outcome variables:
In fact, I'll only review the results of those which I think are particularly pertinent for this review.
The resistance training program involved 12 exercises chosen to include all major muscle groups. Each exercise was performed 3x/week, for 3-4 sets of 4-10 repetitions at approximately 75-90% of one-repetition max (1 RM). Basically, this was a fairly intense workout.
| What Does "1 RM" Mean?
One Rep Max.
|1 RM CALCULATOR|
Enter the amount of weight you can lift (in pounds) and the number of reps you can lift it for.
To measure body composition, the research used a Bod Pod, which I've discussed in a previous article. This is a validated tool to measure body comp, making these results more reliable than if other methods were used.
An ancillary study was then conducted with just a small fraction of the initial 85 individuals; this study was a crossover study, meaning subjects switched groups after a short washout period to ensure any CLA (if they were in that particular group) was cleared from their system.
Overall, males had a significant increase in lean body mass, where females did not. However, there were no differences between CLA and placebo groups for gender and overall body mass over time.
Overall, though, the CLA group did have a greater increase in lean tissue mass, and a greater decrease in fat mass and percent fat compared with the placebo group. This means when all CLA users were pooled together (males and females) vs. all placebo users (males and females) there were no significant differences in strength change among CLA users and non-users.
In the follow-up 7 week crossover study, subjects in the placebo group increased body mass, fat mass and percent fat. However, in the CLA group, these same increases were not observed.
It's also important to note that there were no differences in side effects for CLA vs. placebo users.
The main findings of the first 7-week study were that there was a significant increase in lean body mass and reduction in body fat mass in those in the CLA group. The authors did note that while these were significantly different, they were still relatively small, questioning their clinical significance.
I think these results are very interesting, since they are one of the few studies looking at the relationship between CLA and resistance training; longer studies definitely need to be conducted to ensure that this trend seen in short studies like this continues.
It surely is a promising study, but again, the clinical significance of such small gains in lean body mass or reductions in body fat leave some an open door for longer studies, using similar methodology as this particular study.