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Diet With Protein for People With PKU

Phenylketonuria (PKU) is a genetic disorder of amino acid metabolism, specifically involving metabolic processing of the amino acid phenylalanine. Due either to an impairment, deficiency or complete absence of the enzyme phenylalanine hydroxylase—which would normally convert phenylalanine to tyrosine—excess dietary phenylalanine accumulates in tissues, resulting in profound damage to the body, particularly the nervous system. The critical aspect in management of PKU is strict adherence to a low phenylalanine diet.

  1. Protein Foods and PKU

    • In order to maintain low blood levels of phenylalanine, it is imperative to avoid all foods that are high in protein, as these inherently contain large amounts of the culpable amino acid. Milk and other dairy products, meat, fish, chicken, eggs, beans and nuts should all be completely eliminated. Of course, there are other sources of phenylalanine such as peas, chocolate, pasta, bread, certain fruits and vegetables and the artificial sweetener aspartame, just to name some. It is vital to work closely with a physician and a dietician to determine a safe limit for phenylalanine intake and learn precisely which foods are permitted and in what daily quantities.

    Diet

    • Due to numerous dietary restrictions, individuals with PKU are unable to obtain adequate nutrition from food. PKU does not alter nutrient and energy requirements; these remain the same as in healthy individuals. To provide for nutritional needs, specially formulated medical foods comprise the predominant portion of the diet. These formulas offer the entire assembly of L-amino acids, with the exception of phenylalanine, which is entirely absent. Formula/medical food is the primary source of protein for those with PKU. Some varieties may also contain carbohydrates and fats as well as a range of vitamins and minerals. Depending on the nutrient profile of the chosen formula, it may be supplemented with additional select foods to fulfill daily needs.

      Just as external sources of phenylalanine elevate its blood levels, protein or energy deficiency can do so as well, due to resultant tissue catabolism and subsequent release of phenylalanine. It is thus vital to maintain consistent formula intake and energy balance.

      Phenylalanine is still a necessary amino acid and must be supplied in quantities sufficient for normal growth and development, or maintenance in the case of adults. In order to meet nutritional requiremnts and control blood phenylalanine concentrations, careful food record keeping and frequent blood tests are necessary. The Medical Research Council of the National Institutes of Health established a target range for blood phenylalanine at 2 to 6 mg/dl or 120 to 360 umol/L.

    Low-Protein Food Products

    • A variety of low-protein foods designed specifically for individuals with PKU are available. These include low-protein pastas, breads, cookies, egg replacers, cereals and dessert mixes. Several websites offer such products, including dietspec.com, med-diet.com, ener-g.com, shshna.com and cambrookfoods.com.

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