Body of Evidence

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“More muscle, less fat” is a common theme in bodybuilding circles. Resistance training, cardio, and a healthy diet and supplementation plan usually do the trick, but for an added boost to that time-tested formula, the healthy fat called conjugated linoleic acid — CLA for short — is definitely worth checking out.

CLA was first recognized in 1979 when scientists reported the anti-cancer effects of a beef extract in the journal Cancer Letters. Since then, researchers have learned that the compound has proved consistently useful for helping people in the quest for a better body.

Sum of its Parts

CLA is a group of isomers (that is, different forms) of linoleic acid, the omega-6 fatty acid. Two isomers — awkwardly named c9,t11 and t10,c12 — are particularly well-known for their effects on body composition, among other things. According to a report in the January/February 2009 issue of BioFactors, the c9,t11 isomer, which is sometimes called rumenic acid, comprises 80 percent of the CLA people get from foods like dairy and meat. The researchers noted that while c9,t11 is believed to be the strength behind the cancer-fighting punch of CLA, the other darling of CLA research, the t10,c12 isomer, may be better at affecting cholesterol.

Still, researchers believe that the two work best in tandem, and many commercial CLA formulas contain a combination of both. The combo products are shown in research to have the least risk of side effects, according to Beth Jauquet, RD, CSSD, HFI, the media representative for the Colorado Dietetic Association. “Most of the studies showing a positive effect of CLA have used CLA that is a 50-50 blend of the c9,t11 and t10,c12 isomers,” she says.

Bigger and Leaner

Supplemental CLA has been shown to decrease body fat when it’s combined with resistance training. One report in a 2001 issue of The Journal of International Medical Research showed that men and women who took 0.6 grams of CLA (as Tonalin, which contains equal parts c9,t11 and t10,c12) three times a day and combined that with regular workouts for 12 weeks lost body fat without a change in bodyweight.

CLA also seems to help with adding muscle, as reported in the February 2006 issue of Medicine & Science in Sports & Exercise. The increase in lean mass could be because CLA stymies the breakdown of muscle protein that is a hallmark of training.

“Resistance training results in a small amount of muscle damage and therefore muscle protein breakdown,” explains Philip Chilibeck, Ph.D., co-author of the study and a certified exercise physiologist and professor at the College of Kinesiology, University of Saskatchewan in Canada. “It usually stimulates muscle protein synthesis to a larger extent so that the net effect of resistance training is an increase in muscle mass.”

For Chilibeck’s study, men and women who took 5 grams per day of Tonalin CLA and combined that with resistance training amassed more muscle than folks taking a placebo. What’s more, the men in the study got a boost in bench-press strength, too.

The Skinny on CLA

Perhaps the most heavily touted effect of supplemental CLA is how it battles unwanted body fat. A report in the June 2004 American Journal of Clinical Nutrition showed that overweight adults who took 4.5 grams per day of CLA lost a significant amount of body fat and gained lean body mass over the course of a year — and this was without a structured diet or exercise program.

To investigate further, a second trial was conducted with 134 people from the original study. Compared to the first year in which some people took placebo and some took CLA, for the second yearlong trial, everyone took 3.4 grams per day of Tonalin CLA. Jean-Michel Gaullier, Ph.D., and his co-authors reported in the April 2005 Journal of Nutrition that CLA worked as well during the second year as it had during the first — those who took placebo the first year and switched to CLA saw benefits in terms of body composition, and the people who received CLA for both years reduced their total body-fat mass by 6 percent to 8 percent.

Safety First

The biggest and most important finding from Gaullier’s studies was probably that CLA was safe and well-tolerated for the two-year period. The most common side effect of CLA supplements is stomach issues, but these troubles seem to be equal in studies among people taking the supplement and those taking a placebo. In any case, the effect could be mitigated by taking CLA with food, Chilibeck says, although that tactic hasn’t been studied specifically to date.

Some research has shown that the nonblended form of CLA may increase certain forms of “bad” cholesterol in the blood and may promote insulin resistance. “Much more research in this area needs to be done before conclusions can be reached,” Jauquet says. “Some studies have actually found cardiac benefit from CLA’s ability to improve the blood lipid profile and improve insulin sensitivity. However, most of these studies were done on animals.”

Gaullier’s work did not show any changes in glucose or insulin levels in humans, and another study in a 2003 issue of The Journal of Nutrition showed that CLA may even help people with Type 2 diabetes control their blood sugar levels. Gaullier and his coauthors concluded that based on the research, taking a mixture of the two isomers is likely the best bet.

By the Numbers

Honestly, the exact way CLA works to affect body composition is somewhat of a mystery, and admittedly researchers are still looking into how it works. “The side effects are very mild, and as long as [CLA is] taken safely and properly, there’s very little risk,” Jauquet says.

“It’s important to talk to a doctor or dietician before starting any supplement,” she adds. “You want to make sure that there’s no interaction with another medication, that the supplement is of good quality, that you are taking it correctly, and that it’s not going to interact with another supplement you’re taking.” Jauquet says a safe and effective dose is somewhere between 3 grams and 5 grams per day spread out over three doses and taken with meals.

Clearly, CLA is a multifaceted entity, one that deserves more study. Perhaps there are even greater benefits waiting to be discovered. Meantime, it seems to be abundantly clear that if that old bodybuilding mantra — more muscle, less fat — is your own, using a product such as The Vitamin Shoppe’s Tonalin CLA can be a valuable addition to your supplementation regimen.

CLA’s Bonus Benefits

Research suggests that in addition to improving body composition, CLA may be healthy for several other reasons:

Age-related muscle loss. Dietary CLA may prevent muscle loss that’s typical with aging, and it may also have antioxidant effects, according to a June 2009 animal study published in Biochemical and Biophysical Research Communications.

Atherosclerosis. A May 2009 report in Nutrition, Metabolism & Cardiovascular Diseases showed that eating pecorino cheese, which is naturally high in the c9,t11 CLA isomer, reduces the risk of atherosclerosis (narrowing of the arteries) in middle-aged men and women.

Brain cancer. Dietary CLA prevented a process called angiogenesis, the development of new blood vessels that supports tumor growth, in rats’ cerebellums, leading researchers to conclude in the June 2008 issue of Brain Research that CLA could be a potential therapy for brain cancer.

Diabetes control. CLA that contains equal parts c9,t11 and t10,c12 isomers may help overweight women who have Type 2 diabetes with glycemic control and weight loss, according to a study in the September 2009 American Journal of Clinical Nutrition.