Phenylketonuria is an inherited metabolism disorder that causes a buildup of phenylalanine, an amino acid, due to the absence of the phenylalanine hydroxylase enzyme. This enzyme usually converts phenylalanine into the amino acid tyrosine, causing tyrosine to become conditionally essential to the body. If untreated, the buildup of phenylalanine leads to mental retardation, behavioral problems, seizures and eczema. Luckily, phenylketonuria is treatable by following a restricted-protein diet for life. This diet prevents any further brain damage if strictly followed.
Overview of Diet
The most effective method of preventing further brain damage is to begin the low-phenylalanine diet during your child's growth and development. In order to strictly follow the diet, you must routinely visit with a registered dietitian or doctor who can manage and supervise the progression of the diet. The current recommendation is to follow this diet for life in order to achieve the best possible mental and physical health.
Phenylalanine is found in almost all foods, but milk, eggs and products containing aspartame such as diet soda are extremely high in phenylalanine. Avoid these foods and beverages while on a low-phenylalanine diet.
Low-Phenylalanine Diet
The ideal low-phenylalanine diet provides as much protein as possible to allow for adequate growth and development of your child, while also staying within the recommended blood phenylalanine levels. Your child's physician monitors these levels regularly. Protein in your child's diet comes from fruits, vegetables, rice, cereals and crackers.
When the amount of amino acids needed in your child's diet is calculated, your child's doctor will prescribe him to a metabolic formula containing all of the amino acids in sufficient levels, except the formula will contain an extremely low amount of phenylalanine. Common formula brands prescribed are Phenex, Phenylfree and Lofenalac.
Formula Overview
Special formulas designed for phenylketonuria are usually powder-based and contain a carbohydrate source, fat source with essential fatty acids, vitamins and minerals. Formulas vary in composition according to your age, size, flavor preference and calcium intake. Low carbohydrate and low fat formulas are used for individuals who need to lower their caloric intake due to excessive weight gain, or if aging and decreased growth rates occur. Formulas with minimal vitamin and mineral content are used for those who want a more palatable product, thus requiring a vitamin and mineral supplement. Additional calcium is required if using an unfortified formula due to low dairy intake in phenylketonuria patients.
Considerations
The main considerations in those consuming phenylketonuria-specialized formulas are the problems associated with absorption and nutrient utilization from the synthetic amino acids in the formula powder. A doctor and dietitian should work as a team to minimize nutrient deficiencies, growth retardation, anemia, neuropathy or osteopenia. Amino acid deficiency is another consideration if the diet is restricted too much or if the formula regimen is not advanced often enough.
References
- National Institutes of Health: Phenylketonuria
- "Nutrition Therapy and Pathophysiology"; Marcia Nelms; 2007
- University of Maryland Medical Center: Phenylketonuria
