Twenty inpatients suffering from diabetes mellitus were given prescribed therapeutic diets containing 1,000-1,500 kcal/day and supplemented with 28 mg zinc phosphate for 3 weeks. Twenty outpatients were untreated and were advised to consume specified diets. The results indicated good response for the inpatient group. Elevated levels for insulin and serum zinc were shown, which proved to be statistically significant. Blood glucose, glucagon, and glucose-6-phosphatase levels were reduced significantly due to the diet management and zinc supplementation, while calcium showed no difference. The control group did not show any significant difference in any parameter throughout the study. Our findings suggest that a controlled dietary regimen together with supplementation with zinc might be useful to suppress plasma glucose and to regulate insulin secretion of diabetics.