Effects of synthetic conjugated linoleic acid (CLA) or bio-formed CLA as high CLA beef on rat growth and adipose tissue development

Abstract

Two rat feeding experiments were conducted, concurrently, for 48 d, to determine the effects of feeding synthetic food-grade conjugated linoleic acid (CLA) containing 53% cis 9, trans 11 CLA and 44% trans 10, cis 12 CLA or bio-formed CLA as high CLA beef on adipose tissue development. In exp. 1, 30 (10/diet) weaned male Wistar rats (51 ± 0.65 g) were fed, ad libitum, a control diet, control with sufficient added synthetic CLA to achieve CLA concentrations of 1.1% of diet DM or the control, where the soybean oil in the diet was replaced with sunflower oil. In exp. 2, 20 (10/diet) weaned male Wistar rats (52.5 ± 2.5 g) were fed, ad libitum, diets in which freeze dried beef replaced the casein as the protein source. The meat in the two diets was derived either from steers raised without dietary oil or from beef from steers fed oil to increase CLA content by 144% from 3.36 to 8.20 mg g-1 lipid (high CLA beef). At the end of the experiment the rats were humanely sacrificed and the organs, muscles and the retro-peritoneal and inguinal fat pads were retrieved and weighed. A portion of the fat pad was processed for enumeration of adipocytes while a second portion was used for lipid extraction, and fatty acid composition was determined. In both experiments, diets fed to the rats did not affect rate of growth or carcass, muscle and organ (liver, heart and kidney) weights. In exp. 1, dietary synthetic CLA reduced (P < 0.01) the weight of the retro-peritoneal fat pad and this may have been related to a numerical (-9.8%) but non-significant reduction in feed intake. Although fat pad weight in rats fed sunflower oil was similar to that of rats fed the control diet, the adipocyte number was increased (P < 0.05) by 37%. Dietary supplementation with synthetic CLA, increased (P < 0.05) the CLA concentration in lipids from liver, inguinal fat and retroperitoneal fat of rats. In exp. 2, muscle, organ and fat pad weights were similar for the two meat treatments, but adipocyte number in both pads was lower (P< 0.05) in rats fed the high CLA beef by 40%, which may be a response to dietary CLA and/or a lower protein intake. The lipid from liver and fat tissues of rats fed CLA enhanced beef contained a higher (P < 0.05) CLA concentration than tissues from rats fed the control beef. Data suggest that dietary CLA from either synthetic or high CLA beef may decrease lipid storage potential in fat pads. Key words: Rat, adipose, development, conjugated linoleic acid, high CLA beef