Conjugated linoleic acid does not reduce body fat but decreases hepatic steatosis in adult Wistar rats

The dietary fatty acid conjugated linoleic acid (CLA) reduces hepatic lipid accumulation in some rodent models for obesity and hepatic steatosis. However, these effects are variable and complex due to differences in isomer responses and degree and sensitivity to changes in adiposity. Here, we hypothesized that CLA decreases hepatic steatosis in a diet-induced model of obesity in rats which are resistant to the adipose-lowering effects of CLA. To investigate this, we fed male Wistar rats a high-fat (20%) diet for 4 weeks to induce obesity and hepatic steatosis followed by low-fat (6.5%) experimental diets containing either 6.5% soybean oil (CON) or 1.5% CLA triglyceride mix plus 5% soybean oil (CLA). Dietary CLA significantly lowered hepatic triglycerides without changing weight, adiposity or adipokines, and was associated with significantly lower hepatic fatty acid synthase and stearoyl CoA desaturase-1 (SCD-1) mRNA levels and SCD-1 index along with significantly lower sterol regulatory element binding protein-1 mRNA, a transcription factor that regulates lipogenesis. Furthermore, the lower lipogenesis was associated with significantly higher mRNA expression of lipid oxidation gene peroxisome proliferator-activated receptor-α and acetyl CoA oxidase in the livers of rats fed dietary CLA. The lipid-lowering effects of CLA in the liver were observed in the absence of changes in adipose tissue and body weight. Thus, we conclude that in the Wistar rat model, where adipose levels remain static after feeding dietary CLA, hepatic lipid accumulation is reduced and these effects are not due to an improvement in overall adiposity.