Diet principles - TYR I

The diet for HT1 patients must be individualized depending on each patient’s nutrients requirements. The amount of natural protein allowed in the diet depends on the age appropriate target plasma concentrations, growth rate and anabolism. Close monitoring is essential.

The amount of natural protein tolerated will decrease from 1.8-2.4 g protein kg/day at 4-5 months to around 1 g protein/kg/day, probably related to catch up growth after diagnosis.¹

Average intake of natural protein in HT1¹
1-4 years	0.6g/kg/day	(median 8 g/day)
5-10 years	0,4g/kg/day	(median 8 g/day)
≥11 years	0,2 g/kg/day	(median 14 g/day)

Diet principles^1,2

Limit the intake of natural protein, as the dietary sources of PHE and TYR to maintain blood tyrosine and phenylalanine levels within in the desired range.
Ensure an adequate amount of dietary PHE and TYR, to support normal growth and development but also to maintain blood TYR and PHE levels within the desired range. The TYR tolerance differs within individuals, depending on the level of enzyme defect, growth velocity and (recuperation of) illness.
Adequate amino acid supplementation by a PHE and TYR -free L-amino acid supplement, enriched with micronutrients, essential fatty acids (EFA) up to a level recommended in the age range, in order to maintain adequate protein status for HT1 patients.
Adequate energy intake to promote appropriate growth and weight maintenance and prevent catabolism.
Monitor nutritional status and adjust diet as needed.
Provision of a palatable, varied and ‘easy to maintain’ diet.

References

Dixon M, Macdonald A, White F. Disorders of amino acid metabolism, organic acidae,mias and Urea cycle disorders. In; Shaw V (ed) Clinical paediatric dietetics, 4th edn. John Wiley & Sons ltd. Sussex, 2015:381-526
Van Spronsen Fj, van Rijn G. Tyrosinemie. Carbasius Weber (ed) 1st edn. Dieet bij metabole ziekten 1st Ed. WKZ/UMCU Utrecht. 2011:38-58.