However, some studies have shown that fat-rich diets can actually protect against insulin resistance and T2DM and the fat-rich Atkins diet and other diets are very popular among many people. That means the jury is still out there about the exact role of dietary fat in the development of insulin resistance and T2DM. Similarly, the role of dietary carbohydrates has not been fully established or MS 21570 defined. Some studies have shown that carb-rich diets promote development of insulin resistance and T2DM while others have shown that high-carb diet is protective against insulin resistance and T2DM compared to HFD, and low-carb diet is not necessarily protective against insulin resistance and diabetes. These conflicting results demonstrate the complexity and difficulty in defining the role of each dietary component in insulin resistance and T2DM. In order to accurately address the roles of dietary fat and carbs in insulin resistance and T2DM, several key questions must be answered. First, are dietary carbs necessary for the HFD-induced insulin resistance? Second, how much carb is too much or sufficient to promote the HFD-induced insulin resistance? Third, is fat essential for insulin resistance? In this study, we addressed these questions and the associated mechanisms. As described above, all animals on HFD with or without dietary carbohydrates developed insulin resistance while the animals on chow diet that is a typical high carb and low fat diet did not have insulin resistance. Surwit et al has previously shown that mice on sucrose diet without fat does not intake excess calories and their plasma levels of glucose and insulin are not affected. We and others have previously shown that insulin plays an essential role in the HFD-induced insulin resistance. We asked how important fat was in the development of insulin resistance induced by the chronic exposure to a pathological level of insulin by depriving cells of exogenous and endogenous fatty acids. As shown in Fig. 4A, in the absence of chronic exposure to insulin, the acute insulin treatment induced robust Akt phosphorylation in the presence or absence of fatty acid synthesis inhibitor TOFA in hepatocytes. Note: the effect of TOFA on fat synthesis should be minimal in such a short time as predicted. In MSOP contrast, in the presence of chronic exposure to a pathological level of insulin, the acute insulin treatment induced moderate Akt phosphorylation in the absence of TOFA but stimulated robust Akt phosphorylation in the presence of TOFA. TOFA alone did not influence Akt phosphorylation. Similar results were observed in cultured myocytes. Together, these results demonstrate that fatty acid/fat is essential for the development of insulin resistance induced by the chronic exposure to a pathological level of insulin.