Hyperglycemia among hospitalized patients is associated with an increased risk of mortality and infectious complications. In critically ill patients, hyperglycemia often occurs as a physiological response to stress. For critically ill patients who require nutrition support but have severe malabsorption or intolerance to polymeric formulas, oligomeric formulas may be beneficial. However, hyperglycemia might be a concern with these oligomeric formulas. This study aimed to determine the glycemic index (GI) of a test food, TOP-OP13NPD, a high-protein peptide-based enteral formula. The GI value of TOP-OP13NPD was determined following the protocols outlined in the International Organization for Standardization 26642:2010, involving 10 healthy adults (with an equal proportion of males and females). Both the reference glucose and test food provided 50 g of carbohydrates, and participants’ blood glucose levels were monitored for two hours. After consuming TOP-OP13NPD at 15, 30, 45, and 60 minutes, subjects exhibited significantly lower blood glucose levels than those on the glucose reference diet (p < 0.001). The incremental area under the curve at 120 minutes was also significantly lower compared to the glucose reference diet (1,380.08 ± 276.48 and 3,082.59 ± 677.16 mg × min/dL; p < 0.01). The mean ± SEM GI value of the test food was 48.62 ± 5.86. TOP-OP13NPD is classified as a low glycemic index diet. This result suggests that this formula may be suitable for individuals requiring oligomeric enteral nutrition who need to control their blood glucose levels.