Professional dietary counseling by a nutritionist to young adults with phenylketonuria (PKU) has clear beneficial short-term effects on phenylalanine levels in blood, a study found.
But nutritional counseling should be done at least two times per year to maintain phenylalanine levels in the normal range, as the effects of better diet last for about six months, its researchers suggested.
The study, “Sustaining benefits of nutritional therapy in young adults with phenylketonuria – A 2 year prospective study,” was published in the journal Molecular Genetics and Metabolism Reports.
Phenylketonuria (PKU) is a metabolic disorder caused by a deficiency in the enzyme phenylalanine hydroxylase (PAH).
PAH breaks down an amino acid called phenylalanine (Phe), which is frequently found in diet. People with PKU have elevated Phe levels in their blood, which can lead to intellectual disability and other health problems.
A diet that avoid foods containing Phe, especially in high amounts, is essential. As Phe is an amino acid (a building block of proteins), a patient’s diet is protein restricted, avoiding high protein foods like milk and other dairy products, meat, fish, chicken, eggs, beans, and nuts.
These people are usually given a Phe-free medical formula and amino acid mixtures (AAMs), like special breads and pastas, to make up for the lack of protein in their diet.
Life-long dietary restrictions, however, are difficult, especially for adolescents and young adults taking responsibility over their diet and therapy from their parents.
Younger patients are not as adherent to therapy they need to be, leading to higher-than-normal Phe levels.
A researcher with Children’s Hospital, University of Ulm, in Germany, investigated the long-term effects (24 months) of a consultation by a professional nutritionist on Phe levels in young adults
Daily protein intake, use of AAMs, and micronutrient supply was also assessed.
In total, 21 people, 14 to 30 years old, were included in the analysis. Most were young men; eight were women.
Professional nutritional advice and recommendations were presented in a semi-structured manner to each patient, and tried to follow an individual’s preferences and needs.
Average Phe levels at the study’s start across this group were 926 μmol/l, while normal levels should be below 600 μmol/l in adolescence and adulthood. Six months after meeting the nutritionist, average Phe levels had dropped significantly to 709 μmol/l.
Four patients (38% of the study population) reached values within the therapeutic goal.
After 12, 18 and 24 months, however, Phe levels rose to an average of 869 μmol/l.
The average daily intake of natural protein (found in diet) at baseline (study’s start) was 32.3 g/day. Protein consumption significantly dropped within six months of counseling to 26.9 g/day and to 25.9 g/day at 12 months.
However, this dietary protein’s intake rose to 27.5 g/day at 18 months and 35.0 g/day at 24 months.
Vitamin B12 levels rose to 424.8 pg/ml, from 368.6 pg/ml at baseline, at 24 months, while Vitamin D levels increased to 30.4 ng/ml from 24.5 ng/ml at study’s start.
Patients at baseline were also found to be supplementing their diet with Phe-free amino acids at an average daily consumption of 26.2 g/day.
At all subsequent time points, intake of these supplements was significantly higher: 42.4 g/day after 6 months, 52.1 g/day after 12 months, 38.7 g/day after 18 months and 39.3 g/day after 24 months.
The study, for this reason, found nutritional counseling with recommendations fairly easy to adhere to — like increasing use of amino acid supplements — resulted in adherence for up to 24 months.
“Counselling by a professional nutrionist in young adults with PKU has clear short-term effects on plasma Phe-levels,” the study said.
But the effects on Phe levels seemed to be best for about six months.
“Our study shows a reduction in Phe-levels and reduced amount of intake of natural protein within 6 months in adolescents and young adults with PKU,” the researchers wrote. “But in contrast to generally supposed ongoing effects of counselling by a professional nutrionist, we could clearly show the low half-life of specific changes in nutrition and health behavior after single interventions.”
More frequent nutritional counseling, preferably at least twice a year, is recommended to preserve the long-term benefits of dietary change on Phe levels.
Moreover, it concluded, a “lack of Vitamin B12 and Vitamin D still are common in PKU patients, but [do] not necessarily need to be substituted. They can effectively be equalized by a well-balanced diet within 24 months.”
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