The purpose of this study is to determine whether Rubus occidentalis extract could improve fasting or postprandial serum glucose levels, and related metabolic markers among patients with prediabetes (impaired fasting glucose and/or impaired glucose tolerance).

Inclusion Criteria:

• 19 years of age or older
• prediabetes (fasting plasma glucose 100-125mg/dl, and/or post 75g OGTT plasma glucose 140-199mg/dl)

Exclusion Criteria:

• pregnant women
• taking anti-hyperglycemic agents within 3 months at the time of enrollment
• history of heart failure, myocardial infarction, cerebral infarction
• uncontrolled hypertension (systolic BP > 160mmHg, or diastolic BP > 100mmHg)
• serum triglyceride level > 500mg/dl
• kidney dysfunction (serum Creatinine > 30% of upper normal limits)
• hepatic dysfunction (AST, ALT > 3 times of upper normal limits)
• taking systemic glucocorticoids within 1 month