Objective To analyze the body composition of patients with malignant gastrointestinal tumor and explore the value of body composition analysis in nutrition assessment.

Methods We included 162 patients with malignant gastrointestinal tumor admitted for surgery treatment. Subjective global assessment (SGA) was performed for identifying malnutrition and body composition was analyzed by bioelectrical impedance.

Results The incidence of low fat free mass index, skeletal muscle index and extracellular overhydration were all about 1/4, among which more than 20% patients were classified as well-nourished by SGA. Poor agreement was found between SGA and body composition indexes. However, low fat mass index was better agreed with SGA in male patients while low skeletal muscle index was better agreed with SGA in female patients. Phase angle < 4° had high specificity of 98% for identifying low body mass index, low fat free mass index, low skeletal muscle index, extracellular overhydration, malnutrition, severe malnutrition and hypoalbuminemia.

Conclusion Body composition indexes should be analyzed in the assessment of nutrition status of malignant gastrointestinal tumor patients. Gender difference exists in body composition indexes to indentify malnutrition. Phase angle < 4° has high specificity for comprehensively indentifying malnutrition.