Abstract: Preoperative oral carbohydrates (POC) play an important role in modern anesthesia and surgery as part of enhanced recovery after surgery (ERAS). Oral carbohydrate intake before surgery can reduce preoperative anxiety, improve metabolic status, reduce postoperative insulin resistance, and reduce stress and inflammatory responses in patients, thereby reducing the occurrence of postoperative complications. Directed at a specific population of patients with tumors, an increasing number of studies are focusing on the effects of oral carbohydrate intake before surgery on metabolism, immune function, postoperative complications, and even tumor recurrence. Notably, the direct effect of POC intake on the tumor itself remains unclear. Previous studies have suggested that a reasonable intake of carbohydrates may exhibit an inhibitory effect on tumor development through indirect mechanisms, such as regulating body metabolism and enhancing immune function. This review summarizes and analyzes the perioperative effects of preoperative carbohydrate load in patients with cancer and provides a theoretical basis for the preoperative preparation of these patients.