Abstract
The nutritional and metabolic characteristics of adult phenylketonuria (PKU) patients in the UK with varying dietary adherence is unknown. In other countries, nutritional and metabolic abnormalities have been reported in nonadherent patients compared to adherent counterparts. A pooled analysis of primary baseline data from two UK multi-centre studies was therefore performed to establish whether this is true from a UK perspective. Adult PKU patients who had provided 3-day food records and amino acid blood samples were included and grouped according to dietary adherence (adherent; n = 16 vs. nonadherent; n = 14). Nonadherent patients consumed greater amounts of natural protein compared to adherent patients (61.6 ± 30.7 vs. 18.3 ± 7.7 g/day; q < 0.001). In contrast, the contribution of protein substitutes to total protein intake was lower in nonadherent compared to adherent patients (3.9 ± 9.2 g/day vs. 58.6 ± 10.2 g/day; q < 0.001). Intakes of iron, zinc, vitamin D3, magnesium, calcium, selenium, iodine, vitamin C, vitamin A and copper were significantly lower in nonadherent compared to adherent patients and were below UK Reference Nutrient Intakes. Similarly, intakes of thiamin, riboflavin, niacin, vitamin B6 and phosphorus were significantly lower in nonadherent compared to adherent patients but met the UK Reference Nutrient Intakes. Phenylalanine concentrations in nonadherent patients were significantly higher than adherent patients (861 ± 348 vs. 464 ± 196 µmol/L; q = 0.040) and fell outside of European treatment target ranges. This study shows the nutritional and metabolic consequences of deviation from phenylalanine restriction and intake of PKU protein substitutes in nonadherent adult PKU patients. Collectively, these data further underlie the importance of life-long adherence to the PKU diet.
Highlights
Maintenance of blood phenylalanine concentrations within target range (120–600μmol/L) is recommended to avert the metabolic consequences of phenylketonuria (PKU; OMIM 261600)
The results presented here support previous observations and further confirm that nonadherent adult PKU patients have an insufficient intake of key micronutrients and poor metabolic control compared to adherent counterparts [11,12]
Evidence at present is inconclusive, nonadherence to the PKU diet may impact on the prevalence of overweight and obesity [15], which over time may have implications for increased cardiovascular risk compared to compliant patients [21]
Summary
Maintenance of blood phenylalanine concentrations within target range (120–600μmol/L) is recommended to avert the metabolic consequences of phenylketonuria (PKU; OMIM 261600). This is achieved through a careful, life-long, balance between phenylalanine restriction and intake of lowphenylalanine protein substitutes ( referred to as the PKU diet). Low-phenylalanine protein substitutes are integral adjuncts in the dietary management of PKU They supply around 70–85% of patient’s protein requirements and the majority of essential and large neutral amino acids (in PKU, tyrosine is conditionally essential given the inability to perform phenylalanine hydroxylation effectively), optimise metabolic control and provide a major source of micronutrients [3]. Adherence to a phenylalanine restricted diet and intake of a protein substitute ensures a nutritionally adequate diet whilst enabling metabolic control
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