Biological Effects Of

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In vivo and in vitro investigations with animal/cell models established that CLA was anticarcinogenic for several types of cancer. As research expanded to other biomedical models, a range of additional positive health benefits were identified including antidiabetogenicity, antiatherogenic-ity, immunomodulation, antiobesity, and modulation of bone growth.[7'8] Early work utilized preparations of mixed CLA isomers. More recently, relatively pure preparations of cis-9, trans-11 and trans-10, cis-12

Table 1 Effect of natural and synthetic conjugated linoleic acid (CLA) on tumor development in a rat model of mammary carcinogenesis



Treatment group




28/30 (93%)


Synthetic cis 9, trans 11 CLA

16/30 (53%)


VA/CLA enriched butter

15/30 (50%)

Table 2 Effect of supplements of trans 10, cis 12 conjugated linoleic acid (CLA) on milk fat yield in lactating cowsa and backfat thickness in growing pigsb

trans-10, cis-12 CLA (g/kg dietary dry matter)

Fat variable

Lactating Cows

Milk Fat (g/day)




579 (- 25%)


383 (- 50%)

Growing Pigs

Backfat Thickness (mm)




16.9 (- 20%)


14.6 (- 30%)

aData from Ref. 10. bData from Ref. 11.

aData from Ref. 10. bData from Ref. 11.

isomers have been available, and results indicate they differ in biological activity.

Investigations of the anticancer effect have established that cis-9, trans-11 CLA is anticarcinogenic. In fact, both CLA and VA found in ruminant fat are anticarcinogenic, the latter presumably because it can be converted to CLA via endogenous synthesis. Ip et al.[9] demonstrated that dietary consumption of VA/CLA-enriched butter was effective in reducing the incidence of tumors in a rat model of mammary carcinogenesis (Table 1). These results are among the first to demonstrate that a naturally produced anticarcinogen, consumed as a component of a natural food, is effective in reducing cancer.

Trans-10, cis-12 CLA is a potent inhibitor of milk-fat synthesis in dairy cows (Table 2). This effect is specific for milk fat, and its mechanism involves coordinated reductions in mammary enzymes involved in milk fat synthesis. Effects of trans-10, cis-12 CLA are reversed when supplementation ceases, and the potential to use dietary supplements as a management tool in dairy production is being examined. The ability to selectively reduce milk fat yield could reduce energy demands during times when nutrient intake is inadequate, such as during environmental stress or in the transition period at parturition.[4] In dairy cows, certain dietary conditions also cause a reduction in milk fat, referred to as milk-fat depression (MFD). This is related to unique fatty acid intermediates formed during biohydrogenation, and rumen production of trans-10, cis-12 CLA and its metabolite trans-10 18:1 is increased during diet-induced MFD. Thus, MFD represents a natural situation in which fat synthesis is reduced as a consequence of a diet-induced increase in this specific CLA isomer.

Trans-10, cis-12 CLA has also been shown to reduce body fat accretion in a number of species including pigs (Table 2), although the effective dose is several-fold greater than that needed to affect milk fat. Thus, there is interest in animal agriculture in the potential use of this CLA isomer in the growth period to reduce carcass fat and improve the efficiency of nutrient use.

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