Objectives To evaluate the effects of different diets on the risk of metabolic syndrome. Methods Five groups of female SD rats were fed a normal control (NC) diet, a high-protein (HP) diet, a high-fat diet (HF), a combination high-fat and high-protein diet (HF+HP) or a high-fat with cholesterol diet (HF+CHO), and the changes in body weight, insulin sensitivity and blood biochemical parameters were examined. Results The HF and HF+CHO diets resulted in an increase in body insulin resistance, high blood TG, high blood cholesterol and high blood LDL, with the HF+CHO resulting in larger changes than the HF diet. Furthermore, the HF+CHO diet led to a decrease in HDL, making it the most dangerous diet. However, the HF+HP diet also led to increased blood sugar and some insulin resistance. Conclusions Our findings indicate that the levels of fat and cholesterol should be carefully considered in future diet formulations for patients with or at risk of metabolic syndrome. A high protein diet may reduce the risk of insulin resistance and serum lipid level elevation, but its effects on kidney function remain unknown.