Conjugated Linoleic Acid
Today’s Dietitian
By Leslie K. Kay, MS, RD
Vol. 6 No. 6 p. 44

June is National Dairy Month, designed to increase awareness of the beneficial nutrients found in dairy products. Frequently forgotten on dairy’s nutritional benefits list is a potential powerhouse nutrient abundant in milk fat and cheese and also available as a dietary supplement. Conjugated linoleic acid (CLA) is a naturally occurring derivative of the essential linoleic fatty acid primarily found in foods such as meat, milk, and cheese from ruminant animals (cattle and sheep).

CLA is a collective term used to describe a mixture of positional and geometric isomers (forms) of linoleic acid. The two double bonds in CLA are primarily in the positions 9 and 11, and 10 and 12 along the carbon chain. There can also be geometric changes (cis) or trans configuration. At least eight different CLA isomers have been identified. It is thought that the different isomeric forms might have different physiological effects or health benefits.

CLAIMS
• Decreases body fat
• Fights cancer cells
• Improves insulin levels in diabetic patients
• May lower cholesterol

Many well-controlled animal studies have demonstrated that CLA is significant in reducing body fat, increasing muscle mass, lowering serum cholesterol, inhibiting cancer growth, and preventing or reversing arterial disease. In mice, rats, pigs, and humans, dietary CLA reduces adipose tissue depots.1

WEIGHT LOSS/LEAN TISSUE BUILDER
There’s a lot of interest in using CLA for weight loss in obesity. The ability of CLA to lower adipose tissue is demonstrated in some but not all studies. Michael W. Pariza, MS, PhD, a professor at the University of Wisconsin, Madison, administered 3 grams of CLA to 35 obese adults each day and placebo to another 36 obese adults. Each of the patients in the double-blind study also followed a light exercise program and a diet program. All patients lost an average of approximately 5 pounds over the next six months. But in the one-third of patients who gained lean body mass, the researchers found that those who took placebo regained fat and muscle in a normal 3-to-1 ratio, while those who took CLA regained weight in a 1-to-1 ratio.

Although CLA may help obese people reduce body fat mass, it doesn’t seem to reduce total body weight; however, it may help them keep the weight off after dieting. When used with exercise, CLA may decrease the percentage of body fat, but total body weight is not affected.2

Some studies have demonstrated that CLA supplementation reduces leptin (an enzyme associated with appetite). Researchers believe CLA might reduce body fat deposits by promoting apoptosis in adipose tissue. There is some evidence that only the trans-10, cis-12 isomer has an effect on body fat mass. It is possible that dose, duration, and the composition of the CLA each impact the ability of CLA to affect (modulate) obesity in humans.

Amounts of CLA ranged from 3 to 6 grams per day for up to 12 weeks in overweight and obese subjects. However, doses greater than 3.4 grams per day do not seem to offer any additional benefit.3

CANCER
CLA has been shown to inhibit tumor growth and proliferation of human cancer cells (in vitro). Researchers at Harvard Medical School identified two molecular components (or active isomers) in CLA as potentially influential in the reduction of colorectal and prostatic cancer cells (cis-9, trans-11). The in-vitro results indicate that the cancer-reducing properties of CLA or its constituent isomers are not equivalent. The reduction in cancer cell proliferation appears to be dependent upon the type and concentration of CLA isomer used.4

In animal studies, CLA has shown a cholesterol-lowering and cancer-inhibition effect. It has been investigated for its role in blocking the growth of tissues that support cancer. Specific isomers within CLA exhibit an inhibitory effect on cancer prevention. The reduction seems to be dependent on the type and concentration of CLA isomer used.

There is preliminary evidence that CLA might help reduce the risk of breast cancer. Postmenopausal women who have a higher intake of CLA in foods—particularly cheese—seem to have a lower risk of developing breast cancer.5 More evidence is needed to rate CLA for this use.

DIABETES
CLA is believed to enhance insulin sensitivity and promote glucose uptake.6 While CLA has been shown to reduce fasting insulin in diabetic animals, in nondiabetic subjects CLA had no significant effect on insulin or glucose levels,7 while other studies report an increase in fasting serum insulin in nondiabetic animals and humans.

A 12-week study by Ulf Riserus, PhD,8 investigated the effects of supplementing 3.4 grams per day of a purified (trans-10, cis-12), commercial CLA mixture or placebo could improve insulin sensitivity in 60 obese men with metabolic syndrome. The trans-10, cis-12 CLA significantly increased insulin resistance and glycemia and reduced high-density lipoprotein cholesterol. The CLA mixture did not change glucose metabolism.8

CLA FOUND IN FOOD
Small amounts of CLA may be obtained from the diet (see Table 1). CLA is found naturally in milk fat (typically 5 milligrams of CLA per gram of fat, but can range from 2 to 18 milligrams of CLA per gram of fat) of which the majority is the cis-9, trans-11 isomer form. The richest source is from cheese, Cheez Whiz, and whole milk. When cows are grazed on grass, they have more CLA in their milk than when they are fed the usual barn feed lot. Unfortunately, you would need to eat way too much meat and milk to get amounts of CLA used in research (approximately 5 grams per day). Nonfat products will have little CLA. An average diet supplies 150 to 200 milligrams or more of CLA daily depending on food choices.

SUPPLEMENT TIPS
CLA-containing products sold in health food stores are highly variable in their quality. Some products claiming to contain CLA have been found to contain none at all. Two brands, Tonalin and Clarano, have been used in many research studies and have been shown to contain consistent amounts of CLA through systematic analysis.

CLA is often found along with many other oils in CLA supplements. Some manufacturers formulate CLA in the triglyceride form rather than the free fatty acid form to enhance stability.

CLA can be produced synthetically by exposing oils rich in linoleic acid, such as safflower and soybean, to a base and heat. This CLA product is high in both the cis-9, trans-11 and the trans-10, cis-12 isomers.

Ideally, the CLA content in the Supplements Facts ingredient listings should mention the percentage of CLA and isomer form. For example, Tonalin is a proprietary CLA formulation and among the most researched of the CLA formulations, but it is a blend that contains approximately 74% to 82% CLA. There are various forms or isomers of CLA that may perform different functions. The “trans-10, cis-12” form appears to be the form most associated with changes in body composition. This form and another known as cis-9, trans-11 both show anti-cancer activity. The effectiveness of a CLA supplement may depend on the proportion of the forms present. However, at this time, most products do not specify the ratio of CLA forms present.

— Leslie K. Kay, MS, RD, has worked with the dietary supplements industry since 1985 and is a speaker on the topic of dietary supplements, alternative nutrition, and fad diets.

References for this article are available upon request by e-mailing TDeditor@gvpub.com.

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