Medical foods designed for individuals with inborn errors of metabolism (IEMs) may actually cause harm in patients if their use is not carefully monitored and managed, according to researchers from the National Human Genome Research Institute and the National Institutes of Health (NIH).

A medical food, as defined in the Orphan Drug Act, is regulated as a food by the U.S. Food and Drug Administration and intended to be used under medical supervision. In two studies appearing in the journal Genetics in Medicine, medical foods for isolated methylmalonic acidemia (MMA) and cobalamin C (cblC) deficiency were evaluated for treatment responses and nutrition.

In the MMA study, 61 patients received part or all of their nutrition from a special mix of natural protein and MMA medical foods delivered through feeding tubes. When patients on restricted protein diets were given medical foods to manage MMA, especially in large amounts, patients ended up with four or five times the recommended amounts of leucine that can cause a depletion of the other branched chain amino acids and affect growth and brain development. Additional observational studies suggested that reducing the intake of medical foods can resolve amino acid deficiencies without having to increase the protein intake, but that a cause-and-effect relationship between the amino acid deficiencies and the poor growth outcomes cannot be established as of yet.

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For the cblC research, 28 patients ranging from ages 2–27 received medical foods or protein-restricted diets; both groups had lower growth rates (including decreased head circumference) compared to patients on natural diets providing the recommended daily allowance of protein. A case scenario also showed that increasing natural protein intake and discontinuing methionine-restricted medical foods helped improve head growth and blood amino acid concentrations in an infant with cblC. The authors concluded that there is no theoretical rationale or experimental support for the practice of administering medical foods to patients with cblC deficiency.

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