The prevalence of obesity and Type 2 diabetes has increased dramatically worldwide. Research on Glycemic Index (GI) diets has been largely developed, however the combination with metformin in humans was not investigated yet. We hypothesized that the low-GI diet in combination with metformin would elicit greater improvements on glucose metabolism, lipid profile and body composition on overweight or obese type 1 subjects. This study aims to evaluate the metabolic effects of the adoption of dietary advice to follow caloric restriction high/low GI diets, and low-GI diet associated with metformin on glucose metabolism, lipid profile and body composition on overweight or obese type 1 subjects.

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.

Inclusion Criteria:

• Participants were adults (18-50 y), with body mass index (BMI) between 25-35 kg/m².
• Subjects with adequate glycemic and insulinemic response after oral glucose tolerance test: Hypocaloric diet with predominating high glycemic index foods;
• Subjects with altered glycemic response presented at the 120 min point either glycemia <140mg/dL and insulin level >40 µUI/ml: Hypocaloric diet with predominant low glycemic index foods;
• Subjects with impaired glucose tolerance presented at the 120 min point glycemia 140 - 199mg/dL and insulin >40 µUI/ml: Hypocaloric diet with predominant low glycemic index foods and metformin.

Exclusion Criteria:

• Smokers
• Pregnant or lactating
• Diagnosis of any metabolic diseases
• Were under medication and therapeutic diet, except oral contraceptive for women.