Effects of saturated and polyunsaturated fat enriched diet on the skeletal muscle insulin sensitivity in young rats

The purpose of this study was to evaluate the effect of diets enriched with fat containing different amounts (30% or 60% total energy) of either saturated (SF) or polyunsaturated fatty acids (PUFA) on glucose tolerance in vivo and insulin sensitivity of glucose utilisation by the soleus muscle in vitro. Young rats were maintained for 28 days after weanling on diets containing either sunflower oil (PUFA), animal fat (butter+lard - SF) or the standard laboratory chow (controls). The sunflower oil added to a diet in moderate quantities (30% total energy) improved the total glucose tolerance, while the diets containing high percentage of PUFA (60%) and moderate or high contents of SF caused impairment of glucose tolerance. The diet with 30% of total energy derived from sunflower oil increased the in vitro sensitivity of glucose utilisation to insulin by the soleus muscle, while in contrast, higher proportions of energy given in a form of PUFA as well as the diets enriched with animal fat impaired the sensitivity of this process to insulin. It is also important to note that the synthesis of glycogen in muscles taken from the rats fed high percentage of saturated fatty acid was found unresponsible to insulin. It is concluded that composition of dietary fat has a profound effect on carbohydrate tolerance and the response of muscle glucose metabolism to insulin. It seems likely that this effect may be at least partly mediated by changes in locally produced prostaglandins.