Sarcopenia in pediatric gastroenterology and hepatology: an updated review.

Sarcopenia-the pathologic loss of skeletal muscle mass and strength-is increasingly recognized in pediatric gastroenterology and hepatology as an important determinant of clinical outcomes. Although historically linked to aging, secondary sarcopenia in children arises from chronic inflammation, malnutrition, physical inactivity, corticosteroid exposure, endocrine disturbances, and anabolic resistance. Unlike adult medicine, where diagnostic frameworks are more established, pediatric definitions remain heterogeneous because growth and puberty substantially influence body composition and muscle function. Diagnosis therefore relies on size-adjusted muscle indices, usually normalized to height squared, interpreted against age- and sex-specific reference curves. Body mass index alone is insufficient because muscle depletion and abnormal fat distribution may be present despite normal or elevated body weight, particularly in children with sarcopenic obesity and metabolic dysfunction-associated steatotic liver disease. Accumulating evidence suggests that pediatric sarcopenia is not simply a marker of frailty but a clinically meaningful predictor of adverse outcomes. In pediatric liver transplantation and cirrhosis, sarcopenia is associated with higher waitlist mortality, longer intensive care stays, and more posttransplant infections. In pediatric inflammatory bowel disease, reduced muscle mass correlates with aggressive disease, earlier biologic escalation, and increased surgical risk. This review summarizes current evidence on the epidemiology, pathophysiology, diagnosis, and management of pediatric sarcopenia in gastrointestinal and liver diseases. We discuss available diagnostic tools, including computed tomography/magnetic resonance imaging, dual-energy x-ray absorptiometry, bioelectrical impedance analysis, and grip strength, highlighting their practical advantages and limitations. We also propose a pragmatic diagnostic algoririthm and outline management strategies that extend beyond caloric supplementation, emphasizing adequate protein intake, resistance exercise, and optimization of underlying disease. Early recognition of sarcopenia may improve risk stratification, functional outcomes, and long-term prognosis in children with chronic gastrointestinal and liver diseases.