Background. The most important component of multimodality treatment of cancer is nutritional support. The management of the correct full nutritional support in the perioperative period will help to maintain body weight and muscle function, to reduce the frequency of development of postoperative complication severity and to reduce hospital length of stay. To provide full nutritional support is necessary to cover all energy requirements in patients (30 kcal/kg body weight per day), protein requirements (1.5 g of protein/kg of body weight per day) and eicosapentaenoic acid requirements (2 g/day), applying clinical nutrition through the appropriate routes of administration (oral, enteral, parenteral or combined).
 Materials and methods. The trial studied the dynamics of the nutritional status of 400 oncological patients who underwent surgical treatment at the Hertsen Moscow Oncology Research Institute the branch of the National Medical Research Radiology Centre from 2019 to 2021. The patients were divided into 2 groups: the main (n=200) and the control (n=200). The patients of the main group received full nutritional support. The control group consisted of the patients, according to retrospective analysis of the patients, with the traditional approach to nutritional support. The study included patients with nutritional deficiency confirmed by clinical criteria, as well as patients with malignant neoplasms of the upper gastrointestinal tract the gastrointestinal tract (esophagus and stomach), colon and rectum, as well as head and neck.
 Results. The application of nutritional therapy in the perioperative period can improve the nutritional status of the patients with head and neck and upper gastrointestinal tract cancer (the statistically significant increase in body weight by 1 kgs and 0.5 kgs, respectively). In patients with colorectal cancer, body weight during the treatment was stable with the tendency to increase by 0.4 kg. Perioperative nutritional support for patients with head and neck and upper gastrointestinal tract cancer showed statistically significant increase of the level of both complete protein by 2.8 and 4.1 g/l, respectively, as well as serum albumin by 5.2 and 3.3 g/l, respectively. The absolute lymphocyte count increased at the trend level. No statistically significant difference was obtained during treatment in patients with colorectal cancer. Nutritional support in cancer patients during the surgical treatment allowed to reduce the total number of surgical complications by 36%, including the incidence of anastomotic failure by 3 times (p=0.014), infectious complications by 1.5 times (p=0.074), to reduce the duration of stay in the intensive care unit, as well as inpatient stay in hospital to 0.3 and 1.08 bed days, respectively (p0.05).
 Conclusion. The application of nutritional support can help to reach more favorable perioperative course in cancer patients and also can lead to a decrease in the number of complications and early rehabilitation for patients, and on the other hand, will help to reduce the duration of stay in the intensive care unit as well as inpatient stay in hospital, reducing the cost of treating patients.
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