All groups (Low/High-GI and Low-GI + Metformin) showed significant reduction in anthropometric parameters, but only Low-GI and Low-GI + Metformin groups have an improvement in body composition parameters. In addition, the Low-GI group achieved better results in metabolism of carbohydrates (glucose, insulin, Cederholm Index, and HOMA-β) and lipids (Chol, TAG, LDL-C, VLDL-C, and TC/HDL-c). These results show the benefits of Low-GI diet on metabolic parameters in overweight or obese type 1 subjects.