Background: Nutritional status is a major determinant of outcomes following surgery. Perioperative nutritional supplementation may improve postoperative outcomes, however, studies on the topic have led to controversial results. Methods: Single-centre, feasibility randomized trial among gastrointestinal cancer patients undergoing surgery, comparing perioperative nutritional supplements versus placebo. The supplements included: protein supplementation (preoperative day 30-6), “immunonutrition” (preoperative day 5-1 and postoperative day 1-5), and carbohydrate loading (surgery day). Primary outcome was enrollment fraction (i.e., enrolled/eligible patients). Secondary outcomes were patient compliance with study packages (target > 70% of total packages provided) and 90-day postoperative complication rate, including postoperative infectious complications. A priori, we considered protocol modifications to improve enrollment fraction and compliance. Results: From October 2018 to March 2020, 495 patients were screened, of which, 144 were eligible and 71 were enrolled (enrollment fraction: 49%, 95%CI, 41-57%). Patients did not enroll for various reasons including refusal without reason (n = 33) and too much burden (n = 25). Protocol modifications did not impact enrollment fraction or compliance. Modifications included decreasing the interval from enrollment to surgery from 4 weeks to 2 weeks, and decreasing the complexity and length of the baseline assessment. Median overall compliance was 80%, lower for intervention versus control arm (67% and 87%, respectively). Postoperative complication rates were similar between control (18/31 (58%, 95% CI: 41-74)) and intervention (22/34 (65%, 95%CI 48-79)) arms. There was a trend for lower postoperative infectious rates in the intervention arm (12/34 (35%, 95%CI 22-52)) compared to control (16/31 (52%, 95%CI 35-68)). Conclusions: A trial like this is feasible, with an enrollment fraction of 49% and an overall patient compliance with study packages of 80%. Pilot trial protocol modifications did not increase these proportions. Clinical trial information: NCT03445260.