IRS1 and Insulin resistance: Although no difference in the ratio of the visceral weight to the body weight was observed between wild-type (WT) and Irs1−/− mice fed a HF diet, the results of the insulin tolerance test and oral glucose tolerance test revealed that the Irs1−/− mice fed the HF diet showed severe insulin resistance and marked postprandial hyperglycemia as compared to the WT mice fed the same diet (Figure 2); the liver weight and triglyceride content of the liver were also significantly lower in the Irs1−/− mice than in the WT mice fed the HF diet.