OBJECTIVE: To determine whether a chronic low-glycemic index (LGI) diet, compared with a high-glycemic index (HGI) diet, has beneficial effects on plasma glucose control, lipid metabolism, total fat mass, and insulin resistance in type 2 diabetic patients. RESEARCH DESIGN AND METHODS: Twelve type 2 diabetic men were randomly allocated to two periods of 4 weeks of an LGI or HGI carbohydrate diet separated by a 4-week washout interval, in a crossover design. RESULTS: The LGI diet induced lower postprandial plasma glucose and insulin profiles and areas under the curve than after the HGI diet. At the end of the two dietary periods, the 7-day dietary records demonstrated equal daily total energy and macronutrient intake. Body weight and total fat mass were comparable. Four-week LGI versus HGI diet induced improvement of fasting plasma glucose (P < 0.01, Delta changes during LGI vs. HGI), HbA(1c) (P < 0.01), and whole-body glucose utilization measured by the euglycemic-hyperinsulinemic clamp (P < 0.05). LGI diet induced a decrease in fasting plasma total and LDL cholesterol (Delta changes LGI vs. HGI, P < 0.01), free fatty acids (P < 0.01), apolipoprotein B, and plasminogen activator inhibitor 1 activity. CONCLUSIONS: Only 4 weeks of an LGI diet was able to improve glycemic control, glucose utilization, some lipid profiles, and the capacity for fibrinolysis in type 2 diabetes. Even if changes in glycemic control were modest during the 4-week period, the use of an LGI diet in a longer-term manner might play an important role in the treatment and prevention of diabetes and related disorders.