This clinical study aims to assess feasibility, safety, tolerability, and compliance of a Nonessential Amino Acid Restriction (NEAAR) medical food in adult patients with locally advanced rectal cancer during standard of care short course radiotherapy followed by standard of care chemotherapy.

Inclusion Criteria:

• Histologically confirmed diagnosis of adenocarcinoma of the rectum
• Clinical stage II (cT3-4, N-) or Stage III (cT any, N+) based on MRI
• Eligible for total mesorectal excision
• No evidence of distant metastasis
• No prior pelvic radiation therapy
• No prior chemotherapy
• Age ≥18 years

Exclusion Criteria:

• Patients unable to undergo MRI
• Other anticancer or experimental therapy
• Body mass index (BMI) <18.5 kg/m2 or >40 kg/m2
• Serious or refractive cachexia or anorexia
• Insulin-dependent diabetes Taking or needs to take any protein or amino acid containing nutritional supplements (e.g., Ensure®) Patients with a condition where high-fat or fatty food is contraindicated History of confirmed food allergy Active wound or skin graft that would require a significant increase in protein requirements for skin integrity and healing