It has been hypothesised that glucose intolerance or diabetes can be induced in rodents by a hypercaloric-fat diet or a hypercaloric-sucrose diet. This study was designed to examine the effects of a high-fat diet (HFD: carbohydrates 35-40% kcal, fat 50-55% kcal, protein 10-15% kcal) and a high-sucrose diet (HSD: carbohydrates 65-70% kcal, fat 25-30% kcal, protein 10-15% kcal) compared to a normal or standard diet (ND: carbohydrates 50-55% kcal, fat 15-20% kcal, protein 25-30% kcal) on fasting plasma glucose, glucose tolerance test, plasma triglycerides, plasma cholesterol, body weight, food and water consumption in male Wistar rats. After 4 months, weight gain, plasma triglycerides level, fasting plasma glucose and water intake were significantly elevated (p<0.05) in all test groups when compared to the control group. Total HDL and LDL cholesterol levels were significantly elevated (p<0.05) in the HFD group, whereas the HDL level was significantly lower in the HSD group associated with an atherogenic index significantly elevated (p<0.05) when compared to the control group. After 16 weeks of dietary treatment, an oral glucose tolerance test (OGTT) showed a significant increase in plasma glucose levels after 2-4 h of glucose challenge in all test groups. During the experiment, it was noticed that important weight gain observed in all dietary test groups was associated with a significant low (p<0.05) food consumption. The above results suggest that dietary nutrients contained in these hypercaloric diets might have an effect on insulin action and therefore, might contribute to the development of glucose intolerance and type 2 diabetes. These results also suggest that, in addition to their diabetogenic effect, these hypercaloric diets might probably have an atherogenic effect and could be use in a long-term study to induce type 2 (non-insulino-dependant) diabetes mellitus.