Inborn errors of metabolism are rare genetic disorders in which the body cannot properly turn food into energy. The disorders are usually caused by defects in specific proteins (enzymes) that help break down (metabolize) parts of food.

See: Newborn screening tests

A food product that is not metabolized (broken down into energy) can build up in the body and cause a wide array of symptoms. Several inborn errors of metabolism cause mental retardation if not controlled. There are wide number of inborn errors of metabolism. This article offers a general overview.

Specific information is available on the following forms of inborn errors of metabolism:

• Fructose intolerance
• Galactosemia
• Maple sugar urine disease (MSUD)
• Phenylketonuria (PKU)

Diet changes may control the disorder. The type and extent of the changes depends on the specific metabolic error. For example, persons with galactosemia should avoid milk and milk products, including yogurt, cheese, and ice cream. Galactose and lactose-free milk substitutes and foods should be used.

Health care providers and registered dietitians can help create a diet appropriate for the specific disease.