The PREPARE Pilot randomized controlled trial (RCT) is a multi-center, parallel, blinded RCT that aims to assess the feasibility of a full RCT comparing preoperative very low energy diets (VLEDs) to standard of care prior to elective non-bariatric surgery for obese patients in terms of overall 30-day postoperative morbidity. Adult patients with body mass indices (BMIs) greater than 30 kg/m2 will be randomized 1:1 to receive 3-weeks of preoperative VLED plus preoperative weight loss counselling or preoperative weight loss counselling alone. This trial will enroll patients to assess recruitment, compliance, and follow-up completion to assess the feasibility of a full RCT powered to assess for differences in 30-day postoperative between VLEDs and standard of care arms.

Obesity is a worldwide epidemic affecting upwards of 700 million people. The economic burden in the United States and Canada are estimated at over $2 trillion and $100 billion United States dollars (USD), respectively, and the resultant healthcare consequences can be devastating for systems and patients alike. Obesity is a systemic disease with devastating consequences for patients undergoing any form of operative intervention. Obese patients presenting in need of medical and surgical intervention are at 2-to-6 fold higher risk of prolonged hospitalization, infectious morbidity, venous thromboembolism, and more. To pre-emptively mitigate some of these concerns, prescribed preoperative weight loss via VLEDs has become a standard of care for obese patients undergoing bariatric surgery (i.e., weight loss surgery). While VLEDs have become a standard in obese patients undergoing bariatric surgery, largely due to the significant reduction of peri-organ fat for better visualization, their application to obese patients undergoing other types of surgery remains limited. A previous systematic review and meta-analysis that identified 13 studies evaluating the use of preoperative VLEDs in obese patients undergoing orthopaedic, vascular, colorectal, upper gastrointestinal, gynecological, and a variety of general surgery procedures for benign disease (e.g., cholecystectomy, abdominal wall hernia). While data were heterogenous, preoperative VLEDs reliably resulted in significant weight loss (3.2-19.2kg) with high rates of compliance to the protocols (94-100%). Adverse event rates were low (<14% in most studies). There were no significant differences in postoperative outcomes, though again pooled analyses included a small number of patients and there were wide corresponding 95% CIs. Overall, this review suggested the evidence for routine use of VLEDs in obese patients undergoing major surgery is compromised by heterogeneous small studies with methodological limitations. A large, definitive trial is required to resolve this uncertainty. Prior to a definitive trial to compare the efficacy of VLEDs in obese patients undergoing major surgery, a pilot RCT is required. A pilot trial will provide the following critical feasibility insights: (1) Assessment of recruitment and randomization ability; (2) Evaluation of compliance to VLED regimens; and (3) Assessment of our ability follow patients completely. The objective of this pilot RCT is to determine the feasibility of a multicenter RCT comparing obese patients (i.e., BMI > 30kg/m2) receiving VLEDs versus control prior to elective non-bariatric surgery in terms of perioperative outcomes.

Inclusion Criteria:

• Older than 18 years of age
• BMI of greater than 30 kg/m2
• Undergoing major elective non-bariatric surgery. Major surgery is defined as any operation performed under general anesthesia requiring a skin incision extending beyond the subcutaneous tissue.

Exclusion Criteria:

• Undergoing bariatric surgery
• Undergoing neurologic surgery
• Undergoing urgent or emergent surgery
• Recently diagnosed myocardial infarction or unstable angina (i.e., within past six months)
• Diagnosed moderate-to-severe renal dysfunction (i.e., eGFR less than 30mL/min/1.73m2)
• Diagnosed severe liver dysfunction (i.e., cirrhosis, portal hypertension, hepatic encephalopathy, hepatorenal syndrome)
• Recently diagnosed alcohol or drug use disorders (i.e., excessive use of substance within past six months)
• Experienced a recent episode of gout (i.e., within past six months)
• Medical history of porphyria; (10) Known allergy to any Optifast ingredient
• Enrolled in other prospective studies with similar interventions and/or outcomes. Co-enrollment may be deemed appropriate if the steering committees of the respective trials review the details of participation.
• Pregnant or breastfeeding women
• Patients unable to provide informed consent.

Surgeons, investigators, outcome assessors, and data analysts will be blinded to treatment allocation to limit measurement bias