This is a single-center randomized, placebo-controlled, double-blind feasibility study comparing the intervention of perioperative nutritional supplements (immunomodulation, carbohydrate loading, and protein isolate) with an identical placebo for each solution in patients with gastrointestinal cancer undergoing surgery. Eligible and consenting patients will be randomly allocated to receive the intervention or placebo in a 1:1 ratio.

This study will assess the feasibility of a large, multi-centre trial by establishing the feasibility of randomization to intervention or placebo. This study will be conducted at the Juravinski Hospital and will enroll 100 patients over 18 months.

The study intervention includes three perioperative nutritional supplements: (1) a protein supplement administered 3 times a day for 30 days before surgery, (2) a sugar-based supplement administered the day prior to and the day of surgery, and (3) a formulated liquid diet containing arginine, RNA, proteins and omega-6 fatty acids (referred to as immunonutrition for the purposes of this study) administered for 5 days prior to and 5 days after surgery.

The primary outcome for each eligible patient is defined as being randomized to intervention or placebo. The criteria for success of this study is defined as the proportion of eligible patients randomized as ≥ 60%. If the estimated proportion is <40%, the trial will be considered not feasible. If the proportion is between 40%-59%, the trial will be considered feasible with modifications to improve enrolment. Other secondary objectives include compliance with study intervention, estimating differences in postoperative complications, length of hospital stay, and quality of life between groups.

Inclusion Criteria:

• Men and women 18 years of age or older
• Diagnosed with a resectable type of gastrointestinal cancer (e.g. cancers of the gallbladder, liver, pancreas, stomach, small intestine, colon and rectum) for which an elective operation is planned (resection vs. palliative procedure).
• Patients with distant metastasis are eligible for the study.
• Patients who are lactose intolerant are also eligible for the study because the amount of lactose in ISOlution and PreCovery is minimal (trace).

Exclusion Criteria:

• Malabsorption syndrome (e.g. chronic pancreatitis)
• Cannot tolerate oral intake (e.g. gastric outlet obstruction or delayed gastric emptying)
• Organ failure (liver, kidney); end stage liver disease with a Child Pugh Score ≥ B or end stage renal disease defined as stages 3 and 4 with a glomerular filtration rate between 30-59 for stage 3 and 15-29 for stage 4.
• Inflammatory diseases such as rheumatoid arthritis, systemic lupus erythematous, Crohn's disease and ulcerative colitis
• Patients currently on steroids
• Poorly controlled type 1 or 2 diabetes mellitus
• Female patients who are pregnant and/or lactating
• Galactosemia
• Ongoing infection.