OBJECTIVE: To evaluate the effects of guar gum supplementation in the metabolic control and body mass index (BMI) of type 2 diabetic patients. METHODS: A total of 17 (12 women and 5 men) participants ingested 10 grams of fiber supplement daily for three months. Changes in BMI and the biochemical parameters (fasting glycemia, glycosilated hemoglobin (HbA1c), total plasma cholesterol and triglycerides) were evaluated at the beginning and the end of the study. RESULTS: No changes in mean BMI (p=0.770), mean fasting glycemia (p=0.09) or triglyceride levels were observed. However, significant increases in HbA1c levels were observed (p<0.001) following the ingestion of guar gum supplements. Posterior analysis indicated that the five participants that had the highest mean fasting blood glucose and HbA1c levels, showed a significant reduction in their fasting glycemic levels (p=0.03) at the end of the study. A significant (p<0.001) reduction in total cholesterol levels was observed after three months of guar gum supplementation. CONCLUSION: Guar gum supplementation (10g/day) in the diet of overweight type 2 diabetics, resulting in total fiber ingestion close to 20g per day, did not lead to a spontaneous reduction in body weight. The effect of guar gum on the glycidic metabolic control was inconclusive, but it was shown to be an effective dietetic strategy to reduce blood cholesterol levels.