OBJECTIVE: To examine whether Konjac-mannan (KJM) fiber improves metabolic control as measured by glycemia, lipidemia, and blood pressure in high-risk type 2 diabetic patients. RESEARCH DESIGN AND METHODS: A total of 11 hyperlipidemic and hypertensive type 2 diabetic patients treated conventionally by a low-fat diet and drug therapy participated. After an 8-week baseline, all were randomly assigned to take either KJM fiber-enriched test biscuits (0.7 g/412 kJ [100 kcal] of glucomannan) or matched placebo wheat bran fiber biscuits during two 3-week treatment phases separated by a 2-week washout period. The diet in either case was metabolically controlled and conformed to National Cholesterol Education Program Step 2 guidelines, while medications were maintained constant. Efficacy measures included serum fructosamine, lipid profiles, apolipoproteins, blood pressure, body weight, and nutritional analysis. RESULTS: Compared with placebo, KJM significantly reduced the metabolic control primary end points: serum fructosamine (5.7%, P = 0.007, adjusted alpha = 0.0167), total:HDL cholesterol ratio (10%, P = 0.03, adjusted alpha = 0.05), and systolic blood pressure (sBP) (6.9%, P = 0.02, adjusted alpha = 0.025). Secondary end points, including body weight, total, LDL, and HDL cholesterol, triglycerides, apolipoproteins A-1, B, and their ratio, glucose, insulin, and diastolic blood pressure, were not significant after adjustment by the Bonferroni-Hochberg procedure. CONCLUSIONS: KJM fiber added to conventional treatment may ameliorate glycemic control, blood lipid profile, and sBP in high-risk diabetic individuals, possibly improving the effectiveness of conventional treatment in type 2 diabetes.