Background <p>Gastrectomy due to gastric cancer leads to metabolic alterations in body composition, significantly affecting nutritional status. This prospective study aimed to investigate the metabolic effects of gastrectomy and perioperative treatment on the nutritional status of gastric cancer patients.</p> Methods <p>A total of 37 patients diagnosed with gastric cancer, treated with perioperative chemotherapy, without evidence of dissemination or metastasis, were included in the study. Demographic data, Body Mass Index, full blood count parameters, lipid profiles, vitamin B12, vitamin D, iron levels, albumin, prealbumin, total serum protein concentration, bioimpedance parameters, physical activity levels, quality of life, Prognostic Nutritional Index, neutrophil-to-lymphocyte ratio, and systemic immune-inflammation index were assessed preoperatively and at two follow-ups (6 and 12&#xa0;months post-surgery) for each patient.</p> Results <p>Significant changes were observed across the analyzed parameters, demonstrating the metabolic impact of gastrectomy and perioperative systemic treatment on the nutritional status of gastric cancer patients.</p> Conclusions <p>The study provides a comprehensive evaluation of the long-term nutritional status of gastric cancer patients post-gastrectomy, offering valuable insights into postoperative metabolic and dietary adaptations. Obtained results underscore the dynamic physiological adaptations following gastric resection, emphasizing the importance of nutritional and metabolic monitoring for long-term recovery. Targeted rehabilitation strategies and micronutrient supplementation are crucial in reducing postoperative complications and improving patient outcomes.</p>