By Kim Schoenhals

While we’ve all been told time and again about the evils of fats, the important thing to realize about fat is that it occurs in several forms, and only some of them—such as trans fats—are unhealthful. Certain fats, including conjugated linoleic acid (CLA), can enhance well-being by promoting weight loss and affecting some other facets of human health.

CLA was first identified in the 1980s, when it was isolated from cooked ground beef, one of the most common dietary sources of the nutrient.

“CLA is a polyunsaturated, conjugated fatty acid that is a natural part of the human diet found primarily in beef and dairy products,” says Heather Nelson Cortes, a research scientist at Cognis Nutrition & Health in LaGrange, Illinois, makers of Tonalin CLA. “The CLA content of natural dairy products has fallen over time, and the human body now needs to supplement its consumption of CLA from other sources.”

The average daily intake of CLA is believed to have declined in the United States to about 200 milligrams (mg) per day, which may be contributing to the steady rise of obesity in the country, according to a May 2003 publication from the VERIS Research Information Service. Supplemental CLA may help overweight and obese Americans drop unhealthful pounds for a fitter physique, as well as reduce their risk of heart disease and diabetes.

Supplemental Support
Supplemental CLA has been widely studied for its effects on weight management. To attain the greatest results, clinical studies are conducted with CLA’s biologically active isomers: cis-9, trans-11 (c9,t11) and trans-10, cis-12 (t10,c12).

“It’s important to maximize the two main isomersc9,t11 and t10,c12and minimize any other isomers present,” says Marianne O’Shea, PhD, manager of nutrition and technical services at Lipid Nutrition in Channahon, Illinois, makers of Clarinol CLA.

“By doing this, you have a high concentration of active ingredients and can maximize the effect on the body. It has been demonstrated that mixtures low in these actives are not effective.”

The more prevalent form of CLA in the human diet is c9,t11, although both isomers are available from meat and milk sources. However, CLA isn’t naturally available in very high doses, and it’s primarily consumed in high-fat foods. “In order to obtain the amount of CLA that has been clinically shown to reduce body fat, a person would need to consume large quantities of CLA-rich foods. For example, an adult would need to consume 7.3 pounds of ground beef or 4.3 gallons of ice cream to equal the amount of CLA that has been shown to be efficacious in clinical trials,” says Nelson Cortes.

Shedding the Pounds
Numerous clinical trials have been conducted to elucidate CLA’s role in weight managementand with promising results. A 13-week study involving 54 overweight men and women, for example, showed CLA taken in combination with a very-low-calorie diet induced a higher average body weight loss than placebo, and at both high (3.6 grams per day) and low (1.8 grams per day) doses, CLA also reduced hunger and increased satiety and fullness.

CLA may also help prevent weight regain, as noted by unpublished research using Tonalin. CLA was shown to induce an 8 percent body fat loss after 1 year and maintain that weight loss over the course of a second year. Two additional 12-week studies using Tonalin showed it improved body mass at doses of 3.4 grams per day, and at 4.2 grams per day, it significantly decreased body fat compared to placebo.

Isomer-specific animal research showed the t10,c12 isomerbut not the c9,t11 isomerinduced both body fat loss and adipose apoptosis (programmed cell death of adipose, or fat, tissue), as well as reduced appetite. After 14 days, mice consuming 1 percent mixed CLA or 0.5 percent t10,c12 gained less weight than the control mice and those supplemented with 0.5 percent c9,t11.

“CLA has been shown to reduce body fat by preventing . . . your body from storing fat,” O’Shea said. “It does this by reducing the activity of an enzyme, which acts as a door key on our fat cells. Normally, if we eat more energy than we use, this door is opened by the key, and the fat gets stored. Over time, this can lead to being overweight. When you are taking CLA, the door remains locked, and even though your body absorbs and uses the fat you need to function healthily, excess fat cannot be stored.”

Further Research
Despite the weight-reducing benefits of CLA, some points of caution involving supplementation with the fatty acid have been issued by researchers. One study published in the August 16, 2003 Journal of Lipid Research concluded that while CLA seems to reduce fat mass and increase lean tissue mass, it may induce liver enlargement and insulin resistance. A similar warning was issued by Swedish investigators in the February 2003 issue of Lipids. They said the t10,c12 isomer of CLA “unexpectedly caused a significant impairment of the peripheral insulin sensitivity as well as of blood glucose and serum lipid levels.”

According to O’Shea, supplemental t10,c12 is unavailable to the public, with all CLA supplements offering a combination of the two biologically active isomers. “In the published human studies, a 50:50 mixture of both c9,t11 and t10,c12 have been given in doses ranging from 0.7 gram per day to 6 grams per day for periods of 8 weeks to 12 months,” she said. “In these double blind, placebo-controlled human trials, no adverse effects have been demonstrated as a result of supplementation with the 50:50 mixture of isomers.”

Other Benefits
Aside from its role in weight management, CLA is also discussed for its benefits in other realms of human nutrition, including cancer prevention. Animal research has shown that both biologically active isomers of CLA protect against tumor metastasis, and they may also help prevent breast cancer.

CLA also seems to have antiviral properties. An October 2003 study in the Journal of Nutrition, showed that animals given CLA tended to have less severe pneumonia after a viral challenge compared to animals in the control group.

Additional unpublished research into CLA’s effects on immunity was presented in 2002 at the Office of Dietary Supplements CLA workshop. The human study, which used a proprietary formulation from Lipid Nutrition called Clarinol, showed that 3 grams per day of 50:50 CLA enhanced subjects’ immune responses to a hepatitis B vaccine.

While CLA does possess anticancer and immune-stimulating properties, it’s arguably most popular in the realm of weight management, particularly in light of America’s growing obesity epidemic. By assisting in weight loss, the healthful fat known as CLA has the potential to improve the health of Americans and seems to be a safer option than some previously popular supplements such as ephedra.

“CLA is an alternative to ephedra-based weight-loss products in a time when consumers have a heightened awareness of dietary supplements,” says Nelson Cortes. “As a result, they are choosing products that are safe, do not contain any natural or artificial stimulants and are backed by science.”