We studied the effect of a dietary supplement on blood glucose. This prospective, single-arm, unblinded clinical interventional study investigated the impact of a nutritional supplement combination on fasting glucose and glycated hemoglobin (A1c) levels, which were measured before and after the intervention. The supplement, which consisted of organic mulberry leaf extract, LactoSpore probiotics, and Fenumannan prebiotic, was given to adult (age ≥21 years) prediabetics and adults with type 2 diabetes (A1c >5.60 mg/dL). The study protocol comprised six phases including initial and final tests for fasting glucose and A1c, and a 12-week period of supplement administration. The statistical analyses were carried out using SPSS and Intellectus Statistics. A total of 24 participants completed the study. A reduction of 0.94% in the A1c level and 40.52% in the fasting glucose level were found. These preliminary findings suggest that the nutritional supplement combination might be clinically effective in reducing fasting glucose and A1c in prediabetic adults and those with type 2 diabetes.