This randomized Phase III trial will evaluate whether perioperative nutrition enriched with eicosapentaenoic acid can prevent body weight loss after total gastrectomy for gastric cancer. The patients who enroll in this study will be randomly assigned to Group A: no supplementation with oral nutrients (standard diet) or Group B: standard diet with eicosapentaenoic acid-enriched supplementation for 7 days before surgery and for 21 days after surgery. For both groups, patients will undergo total gastrectomy with Roux-en Y reconstruction. The extent of dissection will principally follow the third edition of the Gastric Cancer Treatment Guideline published by the Japanese Gastric Cancer Association. When patients are diagnosed with pathological Stage II or III disease, adjuvant chemotherapy with S-1 will be initiated within 6 weeks after surgery and administered for 1 year. The primary endpoint will be the body weight loss at 1 and 3 months after surgery (double primary endpoints). The secondary endpoints will be the relative performance of the supplement, loss of lean body mass at 1 and 3 months after surgery, the lowest serum albumin level, quality of life, the incidence of surgical morbidity and mortality, and the incidence of surgical site infection.