Causes of Failure to Thrive
Failure to thrive results from three fundamental mechanisms: inadequate caloric intake (most common), inadequate nutrient absorption, or excessive caloric expenditure, with inadequate intake—often from behavioral, psychosocial, or feeding difficulties—accounting for the majority of cases. 1, 2, 3
Primary Mechanism Categories
Inadequate Caloric Intake (Most Common)
- Behavioral and psychosocial issues are the predominant cause, accounting for inadequate nutrition in 61.4% of cases 4
- Difficulties with nursing or breastfeeding technique 1, 3
- Incorrect formula preparation or concentration 3, 5
- Limited food availability or family food insecurity 2
- Psychiatric and behavioral disorders (17.2% of cases) 4
- Oral-motor dysfunction causing feeding difficulties 6
- Swallowing dysfunction from oromotor coordination problems 7
Inadequate Caloric Absorption
Gastrointestinal disorders are the primary organic causes affecting absorption:
- Celiac disease and inflammatory bowel disease 7
- Pancreatic insufficiency requiring enzyme replacement 7
- Autoimmune enteritis 7
- Food protein-induced enterocolitis syndrome (FPIES), particularly chronic FPIES in infants under 4 months presenting with chronic vomiting, watery diarrhea, and failure to thrive 8
- Gastroesophageal reflux disease (GERD), especially with nasopharyngeal reflux 7
- Esophageal dysmotility and gastroparesis 7
- Severe constipation from intestinal dysmotility 7
Structural gastrointestinal abnormalities:
- Esophageal atresia and tracheoesophageal fistula 7
- Intestinal malrotation, intestinal atresia, anal atresia/stenosis 7
- Hirschsprung disease 7
Excessive Caloric Expenditure
Cardiac disorders increase metabolic demands:
- Left ventricular dysfunction causing pulmonary edema and increased work of breathing 7
- Pulmonary hypertension from chronic hypoxemia 7
Pulmonary/respiratory disorders significantly increase energy requirements:
- Chronic lung disease of infancy/bronchopulmonary dysplasia 7
- Chronic hypoxemia increasing metabolic demands 7
- Increased work of breathing and decreased breathing efficiency 7
- Tracheomalacia and laryngeal anomalies 7
- Aspiration pneumonia from swallowing dysfunction 7
Endocrine and metabolic disorders:
- Hypothyroidism affecting growth velocity 7
- Glycogen storage disease type I causing recurrent hypoglycemia, lactic acidosis, and hepatomegaly 7
- Growth hormone deficiency 7
- Hypocalcemia causing feeding difficulties and irritability 7
Organ System-Specific Causes
Renal/Genitourinary Disorders
- Hydronephrosis and obstructive uropathy 7
- Unilateral renal agenesis or multicystic dysplastic kidney 7
- Vesicoureteral reflux 7
- Renal tubular disorders 7
- Decreased renal function causing sodium/water retention 7
Neurologic Disorders
- Global hypotonia causing feeding difficulties and decreased oral intake 7
- Polymicrogyria and cerebellar abnormalities 7
- Swallowing dysfunction from CNS dyscoordination 7
- Developmental delay affecting feeding skills 7
Genetic/Chromosomal Disorders
- 22q11.2 deletion syndrome with feeding difficulties, cardiac defects, and hypocalcemia 7
- Cardio-facio-cutaneous syndrome with severe feeding difficulties and gastroesophageal reflux 7
- Skeletal dysplasias requiring enteral nutrition in 50% of cases 7
- Shwachman-Bodian-Diamond syndrome with feeding difficulties in 48-73% 7
Hematologic and Immunologic Disorders
- Anemia reducing oxygen delivery and energy availability 7
- Chronic infection from immunodeficiency 7
- Recurrent infections (6.4% of cases) 4
Critical Red Flags for Organic Etiology
When evaluating FTT, specific clinical features strongly suggest underlying organic disease rather than purely nutritional causes:
- Chronic respiratory symptoms including tachypnea, hypoxemia, or increased work of breathing 7
- Vomiting, diarrhea, or signs of malabsorption 7
- Hepatomegaly with metabolic derangements 7
- Dysmorphic features suggesting genetic syndromes 7
Important Clinical Context
Multiple organ systems often interact to cause FTT—for example, pulmonary disease causing cardiac dysfunction, which then causes renal fluid retention, all contributing to poor growth 7. This cascade effect means that identifying one abnormality should prompt evaluation for related complications.
Extensive diagnostic workup rarely identifies the cause: Only 1.1% of laboratory tests, 0.4% of imaging studies, and 1.3% of total diagnostic workup led to a specific diagnosis in one large study, while 27% of endoscopic findings contributed to diagnosis 4. This emphasizes that clinical evaluation and accurate dietary history are far more valuable than routine laboratory screening 1, 2, 3.