Some diets are medications, too.

A clinician should never underestimate the role of diet in a child’s health. A child’s diet must meet basic metabolic functions but also provide adequate nutrition to allow for appropriate growth and development. A pediatrician’s role is to ensure that the child’s diet meets all metabolic and nutritional requirements in the prevention and management of disease, such as iron and vitamin D deficiencies. Diet, as source of treatment, is particularly important for a number of diseases, including phenylketonuria (PKU), epilepsy, diabetes, and renal disease.

Children with inborn errors of metabolism have unique metabolic and dietary requirements. A commonly screened inborn error of metabolism includes PKU. Patients with PKU lack the enzyme used to convert phenylalanine to tyrosine. As serum levels of phenylalanine rise, excessive levels of phenylalanine are transmitted across the blood–brain barrier, leading to deficiencies in the transfer of other essential amino acids. The resultant amino acid deficiencies lead to reduced neuronal protein and neurotransmitter synthesis, impaired brain development, and mental retardation. The mainstay of treatment for patients with PKU is diet; phenylalanine intake is limited with a low-protein diet, and a specific amino acid “cocktail” to provide sufficient amounts essential amino acids. In addition, patients with a metabolic disorder must be monitored for signs catabolism (e.g., intercurrent illness, overexertion, anorexia), as they promote the breakdown of internal protein stores, lead to toxic amounts of a specific substrate, like phenylalanine in PKU. Even a simple viral infection in patients with inborn errors of metabolism can lead to severe acidosis or hyperammonemia, which, in turn, can lead to coma or death. These patients should be treated aggressively at the first sign of illness to avoid (or treat) a metabolic crisis.