Decreased calorie intake • Inadequate or improperly prepared food/formula • Inadequate breast milk supply or ineffective latch • Mechanical feeding difficulties (e.g., cleft palate, neuromuscular disorders) • Diseases causing nausea and vomiting • Acute illnesses causing anorexia or pain with eating (e.g., appendicitis, pharyngitis) • Chronic illnesses causing anorexia or pain with eating (e.g., malignancy) • Psychosocial factors (e.g., food insecurity, neglect or abuse) • Oromuscular dysfunction, oral aversion, feeding disorders, autism • Global developmental delay, central nervous system disorders, genetic syndromes • Psychological disorders (e.g., anorexia nervosa, major depressive disorder) Decreased calorie absorption/utilization • Gastrointestinal malabsorption (e.g., short bowel syndrome, celiac disease, lactose intolerance, cystic fibrosis, inflammatory bowel disease, milk protein allergy, eosinophilic enteropathy, food allergy enteropathy, digestive enzyme deficiency) • Giardiasis, parasitic disease • Liver disease, biliary atresia • Inborn errors of metabolism • Diabetes mellitus (inability to utilize glucose due to the lack of insulin) Increased metabolic demand • Chronic or recurrent infections • Malignancy • Congenital heart disease • Chronic respiratory disease (e.g., bronchopulmonary dysplasia, cystic fibrosis) • Chronic kidney disease, renal tubular acidosis • Hyperthyroidism • Chronic heart and lung disease • Excessive exercise • Immunodeficiency, HIV • Trauma, burns, sepsis (hypermetabolic stress response) Loss of nutrients or water