The distal ileum, where the glucagon-like peptide 1 (GLP-1) releasing cells predominate, is an important organ in mediating glycemic control. However, the distal ileum is not easy to access and the correspond in vivo research remains to be difficult. The investigators intend to recruit subjects who underwent rectal surgery with simultaneous protective ileostomy and evaluate hormone secretion and glycemic excursions via ileostomy glucose or saline infusion, and quantify the glucose absorption rate within the distal ileum.

Inclusion Criteria:

• Male and postmenopausal females aged 18 - 75 years
• Body mass index (BMI) 20 - 35 kg/m2
• With protective ileostomy due to benign or malignant rectal surgery

Exclusion Criteria:

• History of postoperative adjuvant chemotherapy
• Other significant illness, including epilepsy, cardiovascular or respiratory disease
• Impaired renal or liver function (as assessed by calculated creatinine clearance < 90 mL/min or abnormal liver function tests (> 2 times upper limit of normal range))
• Donation of blood within the previous 3 months
• Participation in any other research studies within the previous 3 months
• Females who are pre-menopausal
• Inability to give informed consent
• Vegetarians