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updated July 2005

Conjugated Linoleic Acids

Called CLAs, they were discovered by a friend of mine at the University of Wisconsin-Madison. In research with animals, it was found that CLAs in the diet caused more calories to be directed away from body fat and into muscle development. Whether this occurs in humans, and what dosage might be necessary, is still unknown. But as cited below, mice receiving 0.5% CLA in the diet had about 60% less body fat, and about 10% higher lean body mass. Carnitine, important for fat transport and metabolism, was increased by CLA supplementation. This would permit fat to be metabolized for energy rather than being stored as body fat. The citations below also suggest it is an anti-carcinogen. Note that CLAs are found in human breast milk and regular milk, but are not present in infant formulas. This may be one factor in why breast feeding is better than using formula. They also appear to reduce the risk for colon cancer.

Symposium: Perspectives in Conjugated Linoleic Acid: 2003

1) A Angel, Preface , Am J Clin Nutr 2004 79: 1131S

In various animal models, CLA can reduce or prevent adiposity, improve insulin resistance, inhibit adipogenesis, inhibit tumor development, and modulate inflammatory reactions... Despite all the promising findings, definitive conclusions about the usefulness of CLA in humans as a nutriceutical in the treatment or prevention of chronic diseases are limited. This point is exemplified by significant and unanticipated species variations in the antiadipogenic properties of CLA. Whereas mice are particularly sensitive in a dose-responsive fashion to CLA supplements, recent results of human studies are variable and therefore unconvincing...

Site Author notes. However, the evidence that milk/dairy consumption and breastfeeding substantially reduce weight gain indicate that proper formulation of CLA mixtures has yet to be determined. CLAs include a variety of fatty acid structures, e.g. t10, c12 CLA; c9, t11 CLA; c9, c12 CLA. The latter is linoleic acid. The Symposium has many worthwhile papers. For instance, some studies show a reduction in inflammation, others an increase, probably due to variation in study design. Other studies show reduction in abdominal fat, decrease in insulin resistance-associated cardiovascular disease, and effect on metabolic syndrome. But currently, safety would suggest dairy as the best way to get CLAs in the diet.

"Effect of conjugated linoleic acid on body composition in mice", Park Y; Albright KJ; Liu W; Storkson JM; Cook ME; Pariza MW, Lipids 1997 Aug;32(8):853-8

"The effects of conjugated linoleic acid (CLA) on body composition were investigated. ICR mice were fed a control diet containing 5.5% corn oil or a CLA-supplemented diet (5.0% corn oil plus 0.5% CLA). Mice fed CLA-supplemented diet exhibited 57% and 60% lower body fat and 5% and 14% increased lean body mass relative to controls (P < 0.05). Total carnitine palmitoyltransferase activity was increased by dietary CLA supplementation in both fat pad and skeletal muscle... The effects of CLA on body composition appear to be due in part to reduced fat deposition and increased lipolysis in adipocytes, possibly coupled with enhanced fatty acid oxidation in both muscle cells and adipocytes."

Liew C; Schut HA; Chin SF; Pariza MW; Dashwood RH, "Protection of conjugated linoleic acids against 2-amino-3- methylimidazo[4,5-f]quinoline-induced colon carcinogenesis in the F344 rat: a study of inhibitory mechanisms", Carcinogenesis 1995 Dec;16(12):

"Grilled ground beef contains a number of heterocyclic amine carcinogens,..., as well as anticarcinogenic conjugated linoleic acids (CLA). In the present study, CLA was administered to male F344 rats by gavage on alternating days in weeks 1-4... (100 mg/kg body wt).... CLA had no effect on the size of the foci, but inhibited significantly (P < 0.05) the number of ACF/colon, from 4.3 +/- 2.4 in controls to 1.1 +/- 1.3 in CLA-treated rats ...Collectively, these results support a mechanism involving inhibition of carcinogen activation by CLA"