Dietary sources of conjugated dienoic isomers of linoleic acid, a newly recognized class of anticarcinogens

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Conjugated dienoic derivatives of linoleic acid (CLA), shown to be anticarcinogenic in several animal models, are present in many natural food sources. However, few quantitative data on CLA in food are available. An improved method for quantifying CLA was developed. The method was used to produce a data base of more than 90 food items including meat, poultry, seafood, dairy products, plant oils, and infant and processed foods. The principal dietary sources of CLA are animal products. In general, meat from ruminants contains considerably more CLA than meat from nonruminants, with veal having the lowest and lamb the highest (2.7 vs 5.6 mg CLA/g fat). Foods derived from nonruminant animals were far lower in CLA content except for turkey. Seafood contained low amounts of CLA, ranging from 0.3 to 0.6 mg CLA/g fat. By contrast dairy products (milk, butter, and yogurt) contained considerable amounts of CLA. Natural cheeses were also high in CLA. Among cheeses, those which were aged or ripened more than 10 months had the lowest CLA content. CLA concentrations in an assortment of processed cheeses did not vary much (avg 5.0 mg CLA/g fat). Plant oils contained far less CLA, ranging from 0.1 mg CLA/g fat (coconut oil) to 0.7 mg CLA/g fat (safflower oil). Processed, canned, and infant foods were comparable in CLA content to similar unprocessed foods. Values for foods that contained beef, lamb, and veal were generally high in CLA. However the c-9,t-11 CLA isomer, believed to be the biologically active form, tended to be lower in cooked meats. In animal and dairy products the c-9,t-11 CLA isomer accounted for 75 and 90%, respectively, of the total CLA; in plant oils less than 50% of the total CLA was the c-9,t-1 I CLA isomer. The results show that considerable differences occur in the CLA content of common foods and indicate the possibility of large variations in dietary intakes of CLA.