Inadequate nutritional intake - maternal malabsorption, IDA, neglect
Difficulty feeding - neurological (e.g. cerebral palsy), cleft lip/palate, genetic conditions, pyloric stenosis
Malabsorption - CF, coeliac disease, cows milk allergy, chronic diarrhoea
Increased energy requirements - hyperthyroidism, chronic disease (e.g. CF, congenital heart disease), malignancy, chronic infections
Unable to process nutrients - inborn errors of metabolism (e.g. phenylketonuria), T1DM