<p>Sarcopenia, characterized by loss of skeletal muscle mass and function, is a highly prevalent yet often overlooked condition in patients with gastrointestinal (GI) cancers. Emerging evidence suggests that sarcopenia is a significant predictor of poor prognosis across various stages of GI cancers. Among surgical candidates, preoperative sarcopenia is consistently associated with higher rates of postoperative complications, longer hospital stays, and lower recurrence-free and overall survival rates. Among patients receiving neoadjuvant, adjuvant, or palliative chemotherapy, sarcopenia is associated with increased treatment-related toxicity, reduced adherence to treatment, impaired quality of life, and shorter survival. These findings suggest that sarcopenia is a modifiable risk factor that can critically influence the clinical trajectory of GI cancer patients; i.e., it is not merely a comorbidity. Early detection of sarcopenia through imaging or functional assessment before cancer treatment allows for risk stratification and implementation of targeted interventions such as nutritional optimization and personalized exercise programs. As a primary strategy, the optimal management of sarcopenia in GI cancer patients should combine nutritional and exercise interventions. Pharmacologic therapy, such as anamorelin, may be considered for refractory cachexia accompanied by significant anorexia. Early and sustained multidisciplinary intervention involving collaboration among oncologists, dietitians, physiotherapists, and other specialists is crucial for improving outcomes, enhancing treatment tolerance, and ultimately prolonging survival. This review summarizes the current understanding of sarcopenia in GI cancers, highlights its clinical impact across different treatment settings, and discusses strategies for assessment and integrated management. Addressing sarcopenia is an essential component of personalized cancer care in GI oncology.</p>