BACKGROUND: The impact of preoperative sarcopenia on postoperative outcomes in gastric cancer remains debated. This study aims to perform an in-depth meta-analysis and comprehensive review of the relationship between preoperative sarcopenia, as assessed by the Skeletal Muscle Mass Index (SMI), and postoperative complications and survival metrics in gastric cancer patients, to offer new insights into this issue. METHODS: We conducted a systematic search of primary studies in databases such as Embase, PubMed, and Web of Science, up to July 2024. Our analysis focused on comparing postoperative readmission and mortality rates, overall and severe complication rates, incidence of specific complications, as well as overall survival (OS) and disease-free survival (DFS) between groups with and without preoperative sarcopenia. RESULTS: Our review included 42 studies with a total of 11,981 patients. Findings revealed that patients with sarcopenia had significantly higher rates of overall postoperative complications, severe complications, mortality, and readmissions compared to those without sarcopenia (all P <
0.001). A detailed examination showed that sarcopenic patients had notably higher incidences of pulmonary complications, bowel obstruction, and pancreatic fistulas. Additionally, the OS (P <
0.001) and DFS (P = 0.003) rates were considerably lower in the sarcopenia group. CONCLUSIONS: Preoperative sarcopenia is associated with an increased risk of postoperative complications and poorer survival outcomes in gastric cancer patients. Given these associations, it is recommended to incorporate routine screening for sarcopenia using SMI before surgery, where feasible, to enhance patient risk assessment and customize treatment approaches.