Conjugated linoleic acid is a controversial food
element. It’s been touted as helping build muscle while promoting fat
loss. Structurally, it’s an 18-carbon polyunsaturated fatty acid isomer
derived from the essential fatty acid linoleic acid. While there are 28
identified isomers, or similar compounds of CLA, the two most active
versions are cis-9, trans-11; and trans-10, cis-12. Most commercial CLA
supplements are composed of a mixture of those two isomers. CLA is found
naturally in beef, lamb and dairy foods.
Several animal studies have found that CLA has interesting effects,
such as beneficial changes in body composition and protection against
cancer. The animals used in the studies include rats, mice, pigs and
chickens. Nearly all animal studies show that CLA promotes significant
fat loss.The results of studies done with human subjects are far more equivocal. Some indicate that people respond the same way animals do, while others show few or no changes. The largest human study of CLA, involving 180 subjects, showed that when taken for one year, CLA supplements promoted bodyfat loss and increased lean-tissue mass. Only two previous human studies looked at the effects of combining CLA with exercise. One showed a fat-loss effect; the other showed none. Those differences are often attributed to the composition of the CLA used in the studies, since one isomer of CLA is reputed to promote fat loss more efficiently than the other.
The most recent exercise study of CLA had 76 subjects, who took five grams a day of supplemental CLA or a placebo consisting of seven grams of safflower oil. Both groups trained with weights three times a week during the course of the study. After seven weeks, 17 of the subjects switched to the other group, making it a crossover study.
After seven more weeks those in the CLA group showed greater increases in lean mass, greater loss of bodyfat and less muscle loss. The only strength change was an increase in bench press strength in the male subjects. The CLA appeared to exert an anticatabolic effect in muscle. How it does that isn’t known, but several theories are offered, including the following:
- CLA may modulate the immune stress response, possibly by interacting with cortisol release.
- CLA may blunt the release of inflammatory substances linked to muscle breakdown.
- Increasing resting energy expenditure by stimulating the activity of thermogenic proteins known as uncoupling proteins.
- Interfering with the activity of the fat-cell enzyme lipoprotein lipase, which blunts the amount of fat that can be stored in fat cells.
- Increasing the activity of the enzyme that works with L-carnitine in shuttling fat into the mitochondria, where fat is burned.
- Preventing new fat cells from forming by inhibiting the actions of fat-promoting genes.
- Lowering levels of leptin, a protein produced in fat cells that helps to regulate food intake and energy usage.
This study suggests that while CLA may be somewhat useful in conjunction with a weight-training program, its effect is small and, as the authors noted, not comparable to other supplements, such as creatine. What needs to be done now is to test the individual active isomers of CLA to see which works better for purposes of fat loss and muscle gain.
Pinkoski, C., et al. (2006). The effects of conjugated linoleic acid supplementation during resistance training. Med Sci Sports Exerc. 38:339-48.
©,2012, Jerry Brainum.Any reprinting in any type of media, including electronic and foreign is expressly prohibited.
