A 62-year-old woman undergoes distal gastrectomy with D2 lymphadenectomy for T3N2 gastric cancer of the antrum. Intraoperatively, the tumor is found to directly invade the pancreatic head. The surgeon performs an en bloc distal pancreatectomy along with splenectomy to achieve R0 resection. Postoperatively, the patient develops severe hyperglycemia (fasting glucose 320 mg/dL) and steatorrhea. What is the most likely cause of these complications?