Can Conjugated Linoleic Acid (CLA) Improve My Health?

Conjugated Linoleic Acid (CLA) occurs naturally in whole milk and red meat. A collective term used to designate a mixture of positional and geometric isomers of the essential fat linoleic acid. It is actually a fat, derived from linoleic acid (an essential fatty acid). Studies have shown that CLA can increase lean body mass and decrease fat, inhibit the growth of tumors and enhance immune function. CLA is found naturally in beef, cheese and whole milk.

The role of diet in the development of cancer has been the focus of much scientific research during the past decade. Researchers now know that high intakes of certain naturally occurring dietary chemicals increase our risk of cancer. Such chemicals include benzo(a)pyrene (found in charcoal-broiled meat), aflatoxin (found in peanuts), and certain hydrazines (found in edible mushrooms). But scientists studying the chemical makeup of the human diet have also identified some naturally occurring anticancer chemicals. One looks especially promising.

New results on the physiological properties of conjugated linoleic acid have been published by several working groups, especially showing the effects of single conjugated linoleic acid isomers on carcinogenesis and body composition. Recently, other studies have shown that conjugated linoleic acid has an influence on diabetes mellitus, platelet aggregation and the immune system.

Conjugated linoleic acid has been shown to inhibit carcinogenesis and therosclerosis, enhance immunologic function while protecting against the catabolic effects of immune stimulation, affect body composition change (reducing body fat gain while enhancing lean body mass gain), and stimulate the growth of young rats. We discuss possible biochemical mechanisms that underlie these physiological effects. We emphasize the importance of considering the effects, both individually and combined, of the two CLA isomers (cis-9, trans-11 CLA and trans-10, cis-12 CLA) that have been shown to exhibit biological activity and which appear to exert their effects via different biochemical mechanisms.

The optimum approach to conquering cancer is prevention. Although the human diet contains components which promote cancer, it also contains components with the potential to prevent it. Recent research shows that milk fat contains a number of potential anticarcinogenic components including conjugated linoleic acid, sphingomyelin, butyric acid and ether lipids. CLA inhibited proliferation of human malignant melanoma, colorectal, breast and lung cancer cell lines. In animals, it reduced the incidence of chemically induced mouse epidermal tumors, mouse forestomach neoplasia and aberrant crypt foci in the rat colon. In a number of studies, conjugated linoleic acid, at near-physiological concentrations, inhibited mammary tumorigenesis independently of the amount and type of fat in the diet. In vitro studies showed that the milk phospholipid, sphingomyelin, through its biologically active metabolites ceramide and sphingosine, participates in three major antiproliferative pathways influencing oncogenesis, namely, inhibition of cell growth, and induction of differentiation and apoptosis. Mice fed sphingomyelin had fewer colon tumors and aberrant crypt foci than control animals. About one third of all milk triacylglycerols contain one molecule of butyric acid, a potent inhibitor of proliferation and inducer of differentiation and apoptosis in a wide range of neoplastic cell lines. Although butyrate produced by colonic fermentation is considered important for colon cancer protection, an animal study suggests dietary butyrate may inhibit mammary tumorigenesis. The dairy cow also has the ability to extract other potential anticarcinogenic agents such as -carotene, -ionone and gossypol from its feed and transfer them to milk. Animal studies comparing the tumorigenic potential of milk fat or butter with linoleic acid-rich vegetable oils or margarines are reviewed. They clearly show less tumor development with dairy products.

In this review of the effects of trans fatty acids, oleic acid, n-3 polyunsaturated fatty acids, and conjugated linoleic acid on mammary carcinogenesis in animals, the goal is not to provide an exhaustive survey of all the publications on these topics; such a Herculean effort has been accomplished by previous reviews, which are cited in the text. Instead, the emphasis is on the consistency or lack of consistency of information regarding each of the above fatty acids, confounding factors that may help to reconcile discrepancies in the database, a perspective of the history of the research, and certain unique or exciting opportunities that are worthy of special attention in evaluations of the relations between specific fatty acids and cancer. This review arrives at four conclusions:

  1. There is little evidence that trans fatty acids have an adverse effect on carcinogenesis.
  2. The data on cancer protection by oleic acid are not convincing. An inhibitory effect attributed to an increased intake of oleic acid could be due to an inadequate supply of linoleic acid.
  3. Although a suppressive response to n-3 polyunsaturated fatty acids is observed in most cases, the availability of linoleic acid is likely to be a confounding factor in determining the final outcome.
  4. Conjugated linoleic acid is unique in the sense that concentrations of less or = 1% are sufficient for producing significant cancer protection and that this effect seems to be independent of the other fatty acids.

CLA may also prevent diabetes, according to a research team from Purdue and Pennsylvania State universities. This information could lead to new drugs to help fight diabetes, or to improved dietary strategies to manage diabetes, the researchers say. The study found that conjugated linoleic acid can prevent the onset of diabetes in laboratory animals, at least in the short term. The researchers say CLA appears to work as well as a new class of diabetes-fighting drugs, the thiazolidinediones, or TZDs. Martha Belury, Purdue assistant professor of foods and nutrition, says: "If you inherit a genetic predisposition to adult-onset diabetes and you're obese and inactive, then you may well develop this disease. Our study suggests that CLA may help normalize or reduce blood glucose levels and prevent diabetes."

  • Michael W. Pariza, Yeonhwa Park and Mark E. Cook. Mechanisms of Action of Conjugated Linoleic Acid: Evidence and Speculation - Food Research Institute, Department of Food Microbiology and Toxicology, University of Wisconsin-Madison
  • Peter W. Parodi. Cows' Milk Fat Components as Potential Anticarcinogenic Agents - Human Nutrition Program, Dairy Research & Development Corporation, Glen Iris, Victoria 3146 Australia
  • American Journal of Clinical Nutrition, Vol 66, 1523S-1529S - Review of the effects of trans fatty acids, oleic acid, n-3 polyunsaturated fatty acids, and conjugated linoleic acid on mammary carcinogenesis in animals
  • Purdue News 1998 - Compound in meat prevents diabetes, study suggests