[Effects of high-fat diets based on butter or soybean, olive or fish oil on insulin resistance and plasma desacyl-ghrelin in rats

There is evidence on reciprocal effects of insulin and desacylghrelin [DAG], but associations between secretions of hormones [insulin and DAG] and saturated and unsaturated proportions of edible oils in high-fat diets have not been studied. The aim of this study was to investigate the impact of different sources of dietary fat and the extent of fatty acid saturation on plasma insulin and DAG levels and determine the association between DAG and insulin action in rats. Weaning male Wistar rats were randomly divided into four groups to be fed on one of 4 high-fat diets containing, as the source of fat, butter [HF-b], soybean oil [HB-S], olive oil [HF-O], or fish oil [HF-F]. A fifth group was put on a standard diet [SD]. Blood samples were collected after 8 weeks at non-fasting state and after a 24h fast. Body weight, food intake, and plasma parameters - glucose, insulin, DAG, and HOMA-IR, as an insulin resistance index - were measured. Body weight and food intake in the HF-S and HF-B groups were higher than in the other groups [p<0.05]. In the HF-B group the fasting insulin level and HOMA-IR were both higher as compared to the ST, HF-O or HF-F group [p<0.05]. In addition, the fasting DAG level in the HF-B group was lower than in HF-F, HF-O or ST group [p<0.05]. Finally, the HF-F group had a significantly higher DAG level than the HF-S group [P<0.05]. Diets containing polyunsaturated omega -3 and monounsaturated fatty acids cause lower weight gains and energy intakes. It is likely that these dietary fats could bring about a decrease in appetite through increasing the DAG level, thereby causing weight reduction. It is concluded, then, that they may have a role in lowering HOMA-IR or insulin level