Table 1 Types of protein substitutes suitable for children < 6 years of age
Stage | Type | Features | Issues |
|---|---|---|---|
1 | Infant protein substitutes (powder/liquid) L-amino acids | • Phenylalanine-free • Given post neonatal diagnosis • Early infant exposure accustoms their taste to amino acids [4] | • Poor taste [4] |
2 | Semi-solid weaning protein substitutes L-amino acids | • Phenylalanine-free • Semi-solid consistency given from a spoon • Higher in protein equivalent than infant protein substitutes • Introduced from 6 months • Low volume/low energy so infant has capacity/appetite for solid foods [5, 6] | • Poor taste but most infants adapt if introduced at 6 months • Difficult to administer during teething/illness • Thickens on standing • High osmolality [5] |
2/3 | Powders suitable from 1y+ L-amino acids | • Phenylalanine-free • Concentrated in amino acids so low volume • Flexible as the amount of water added can be adjusted and it is usually given as a drink [4, 6] | • Poor taste • Less convenient • Needs water for preparation • High osmolality [7] |
3 | Ready to use liquid protein substitutes L-amino acids | • Phenylalanine-free • Low volume • Convenient | • Poor taste |
3 | Casein glycomacropeptide with amino acids (CGMP-AA) Peptide based substitute with added amino acids | • Low-phenylalanine • Powdered, liquid and bars • Improved taste and palatability • May improve nitrogen retention • Prebiotic, antimicrobial and immunomodulatory effects [9,10,11,12,13] | • Contains residual phenylalanine • May increase blood phenylalanine in well-treated children if given as a sole source of protein substitute • Human studies on long-term effects are limited [1, 14,15,16] |
3 | Slow-release protein substitutes suitable from 3 +  Amino acids coated with ethyl cellulose and alginate | • Phenylalanine-free • Granules • Mixed with food or fruit juice • Prolonged release and physiological absorption of amino acids shown in a non-PKU human study |