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Setting the record straight on CLA

June 8, 2009

Naturally occurring CLA and related vaccenic acid obtained from dairy and beef products show remarkable health potential, distinct from nutraceutical supplements.

Dr. Spencer Proctor
Dr. Spencer Proctor

What is the truth about the health value of CLA?

With various forms of conjugated linoleic acid (CLA) now available and more recognizable to consumers, this question is more relevant than ever.

Sorting out the truth is no easy task, for a variety of reasons.

Among them, the science investigating the health value of CLA is, overall, in early stages. Meanwhile, the nutraceutical supplements industry has at times pushed the envelope in touting CLA-related weight loss and other health claims.

Added to this is potential for confusion related to natural forms of CLA obtained through foods versus the manufactured forms mass produced for supplements.

This creates the risk of misinterpreting findings from nutraceutical studies as having implications for CLA found in foods. One article raising concern over natural CLA, based on findings from a nutraceutical supplement study, was a story headlined "Natural trans fat shares artificial version's bad rap," published in The Medical Post earlier this year. In the study discussed, a CLA enriched oil was manufactured into foods, to provide very high doses of CLA to participants. It should be stressed that the dosage of CLA used in that study has no clinical nor physiological implications for the population at large, which consumes much lower levels of naturally derived ruminant trans fat through normal consumption of dairy or beef products.

To provide a clear picture of what is understood about the health value of natural CLA, two of the best sources available are Dr. Spencer Proctor, Director of the Metabolic and Cardiovascular Diseases Laboratory at the Alberta Institute for Human Nutrition, based at the University of Alberta, and Dr. Benoit Lamarche, a Canada Research Chair in Nutrition and Cardiovascular Health based at Université Laval.

Both are internationally recognized leaders in studying the health implications of natural ruminant trans fats, including CLA and the CLA pre-cursor vaccenic acid. They are also colleagues in the CLA Network, a Canada-based multi-disciplinary network linking diverse areas of progress in understanding the health potential of natural CLA and related ruminant fatty acids and lipids.

While several studies, such as the one cited in the "bad rap" article, indicate negative health consequences of consuming very high levels of CLA nutraceutical supplements, this in no way relates to natural CLA obtained through foods, say Proctor and Lamarche.

"Natural and nutraceutical forms each have very different chemical structures," says Proctor. "Natural forms are produced only by ruminant animals and occur naturally in related milk and meat products. They are also consumed at low levels compared to the high levels that could theoretically be consumed in supplement forms."

Studies of nutraceutical supplements have merit in that specific context, but it's a mistake to relate the findings of those studies in any way to implications for natural CLA, and indeed other natural trans fats found in foods, he says.

Research-based knowledge of natural CLA obtained through regular food consumption does not support the view that CLA is a "bad" fat, says Lamarche. "Based on the science, there is no substantial concern related to natural CLA in foods. In fact, emerging data in the literature suggests that natural CLA and other ruminant trans fatty acids may even perhaps play a beneficial role in health and disease. However, research in this area is in its early stages and more evidence is needed to further validate this hypothesis."

One such study indicating no substantial health risk related to ruminant trans fats, conducted in a double-blind, randomized, crossover controlled design with healthy male subjects, was conducted by Lamarche and his Université Laval colleagues and recently published in the American Journal of Clinical Nutrition (Motard-Belanger et al. Am J Clin Nutr 2008;87:593-599). They have shown that intakes of natural ruminant trans fat at levels that are well above the current intakes but still achievable by the population had no impact on all main risk factors for cardiovascular disease.

A recent statement by the World Health Organization suggests there is currently no concern regarding the intake of natural ruminant trans fat in foods at levels consumed by the population.

This statement along with a few additional recent examples of relevant publications of particular interest to researchers and health professionals, are cited in brief form here:

Natural and nutraceutical chemically different

When assessing CLA health implications, a critical distinction sometimes missed is the fact there are many different 'isomers' or types of both natural and manufactured CLA, say the two scientists.

Running in the right direction: Natural CLA shows health enhancing potential.
Running in the right direction: Natural CLA shows health enhancing potential.

Natural CLA is only produced when ruminant animals, such as dairy and beef cattle, feed on grasses and other plant material. During the digestion process, linoleic acid, an essential omega-6 fatty acid, is released and converted into CLA upon interaction with internal microorganisms. (Hydrogen is added, forming "conjugated" linoleic acid or CLA).

In the case of natural CLA, over 20 different isomers have been identified so far. However, it is specifically the isomer "CLA 9,11" that is the predominant form of CLA in dairy and beef products. CLA 9,11 and vaccenic acid combined make up the vast majority of natural ruminant trans fatty acids in dairy and beef products and both have been linked to remarkable health enhancing potential.

Research to date, based primarily on animal models and cell culture studies, has revealed that natural CLA 9,11 contains antioxidant, anti-tumor and other health-boosting properties, with strong promise to deliver health benefits beyond nutrition. These potential benefits include helping to prevent or fight cancer, heart disease, obesity, diabetes, kidney disease and metabolic syndrome, and to improve bone density.

Among key findings, in studies using animal models conducted by Proctor and colleagues, feeding CLA was associated with improved blood lipid profiles including a reduction in high levels of LDL. (Proctor et al. 2006.) "Synergistic effects of conjugated linoleic acid and chromium picolinate improve vascular function and renal pathophysiology in the insulin-resistant JCR:LA-cp rat." Diabetes, Obesity and Metabolism 9(1):87-95.)

There has been less research into vaccenic acid but studies to date with that focus have likewise produced encouraging evidence of health-enhancing potential. In one important recent example, an animal model study showed feeding of vaccenic acid was associated with a substantial lowering of triglyceride levels (Wang et al. 2008. "Trans-11 vaccenic acid dietary supplementation induces hypolipidemic effects in JCR:LA-cp rats." Journal of Nutrition 38(11):2117-22.)

Additional benefits to cholesterol metabolism have been found by the same research team with longer-term feeding of vaccenic acid (currently under scientific review).

Also, further results have indicated CLA may influence an inflammatory-related mechanism that reduces the disease pathology (Proctor et al. 2006. Diabetes, Obesity and Metabolism 9(1):87-95.)

Supplement forms of CLA are also available and marketed with various implied health claims. However, the mass produced forms typically contain mixed isomers, often with synthetic (such as CLA 10,12) forms as a key component.

Even when supplements include a portion of CLA 9,11, obtaining CLA through a supplement is distinctly different from obtaining natural dairy and beef CLA through food products, says Proctor. "It would be a mistake to draw any connection between findings related to supplements and what that means for people who regularly consume natural ruminant trans fatty acids through food."

Body of evidence supports natural CLA benefits

The promising research results with natural CLA, vaccenic acid and ruminant trans fats in general, are driving increased research interest in this area globally. They have also provided a basis for some of the first human clinical trials in this area, planned over the next several years.

Among the new research in preparation, a $2 million grant was recently awarded to Proctor's research program to further investigate CLA and vaccenic acid, in both a basic and human context, in several studies over the next five years.

"Based on our research to date, we're very confident we're seeing not only the absence of negative effects but also clearly positive health effects related to natural ruminant trans fatty acids obtained through food," says Proctor. "This next wave of research will help us both confirm and further understand this potential."

This research is of tremendous significance, observe the two researchers. Vaccenic acid is estimated to contribute 70 to 80 percent of ruminant-based trans fat in the North American diet. (Lock, A.L., Bauman D.E. 2004. Lipids 39: 1197-1206. Also: Cruz-Hernandez et al. 2007. Journal of Dairy Science 90: 3786-37801.)

Vaccenic acid is currently included in trans fat calculations that appear on the labels of foods, including dairy foods. "The trans fat in dairy and beef is often incorrectly viewed as a negative when in fact it this component does not appear to be harmful at all," says Lamarche.

As further reinforced by the recent Université Laval study, it is clear that ruminant trans fatty acids in the context of their actual consumption level do not induce the specific potentially harmful properties associated with industrially processed trans fat, observes Proctor. In the case of natural CLA, that recognition is a reason why health authorities in Canada, the U.S., and numerous other countries have decided not to include CLA in the trans fat calculations that appear on food labels. Vaccenic acid, however, is currently included, in part because there has been less knowledge until recently.

"As more research knowledge emerges, our hope is there will be improved health information available to consumers, including labeling information, that reflects the critical distinction between natural trans fat and industrial forms," says Proctor.

This item was prepared by the CLA Network. More information on the CLA Network is available at

Reprintable with credit to the CLA Network.

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