Establishing a prescription is done in a stepwise manner:

Step 1	Fill the PHE requirements through the use of measured quantities of natural protein from breast milk, regular infant formula in infants and by natural food intake beyond infancy
Step 2	Fill the protein requirement by adding the PHE-free L-amino acid supplement that provides a PHE free mixture of amino acids, and other nutrients
Step 3	Fill energy requirements by adding non-protein calorie sources as needed. Energy needs should be based on ideal body weight whenever possible and are the same as for non-PKU patients
Step 4	Adjust fluid volume to meet requirements
Step 5	Calculate vitamins, minerals, trace-elements, essential fatty acids content of the final supplement, adjust or supplement as needed

Dietary recommendations:

Protein recommendations

For healthy individuals, protein recommendations are based on the rates of growth, protein deposition for children of different age groups, the amino acid composition of whole body protein, as well as the efficiency of dietary protein utilization1 and more recently by a stable isotopic technique.2

In PKU patients the majority of patients will take the PHE-free protein supplement, that will provide approximately 75% of total protein intake3.

The optimal protein intake is not agreed, where some will allow an inefficiency factor for L-amino acid sources of 20%4

Amino acids do not require digestion and are directly available for absorption by the small intestine, which leads to rapid absorption and cause a transient imbalance of amino acids in the systemic circulation as opposed to whole protein intake5,6.

ESPKU preliminary recommendations for Protein:

Total protein intake should supply age-related safe levels of protein intake, based on WHO/FAO/UNU2007, with an additional 20% of L-aminoacids to compensate for the ‘digestible indispensable amino acid score and further 20% to optimize impact of L-AA on blood Phe control.

Age	gProtein/kg bodyweight
0-2 months	2,5
2-12 months	2,0
1-4 years	1,5
4-10 years	1,2
10-14 years	1,1
>14 years	1,0

Energy requirements infants		Energy requirements children
Age/months	Kcal/kg/d	Age years	Kcal/kg/d – M	Kcal/kg/d – F
1	110	1-2	82	80
2	102	2-3	84	81
3	95	3-4	80	77
4	83	4-5	77	74
5	82	5-6	75	72
6	81	6-7	73	69
7	79	7-8	71	67
8	79	8-9	69	64
9	79	9-10	67	61
10	80	10-11	65	58
11	80	11-12	62	55
12	80	12-13	60	52
		13-14	58	49
		14-15	56	47
		15-16	53	45
		16-17	52	44
		17-18	50	44
		<18

Human energy requirements, report of a joint FAO/WHO/UNU Expert consultation. October 2001.

Fluid requirements, based on requirements of healthy population
Age	Weight (kg)	Recommendation (ml)
0-3 months		150 x weight (kg)
4-6 months		130 x weight (kg)
7-9 months		120 x weight (kg)
10-12 months		110 x weight (kg)
>1 year	1-10	100 x weight (kg)
	11-20	1000 + 50 x (weight in kg -10)
	> 20	1000 + 20 x (weight in kg – 20)

Human fluid requirements Report of a Joint FAO/WHO/UNU expert consultation 2001.

References

Pillai RR, Kurpad AV Amino acid requirements in children and the elderly population. Br J Nutr, 2012, 108(Suppl 2) S44−9.
Lango R, Levesque C, Ball RO et al. Available versus digestible amino acids − new stable isotope methods. Br J Nutr, 2012, 108(Suppl 20) S306−14.
Hennermann JB, Roloff S, Gellermann J et al. Chronic kidney disease in adolescent and adult patients with phenylketonuria. J Inherit Metab Dis, 2013;36(5):747-756.
MacDonald A, Rocha JC, van Rijn M et al. Nutrition in phenylketonuria. Mol Genet Metab, 2011, 104(Suppl) S10−18.283.
Gropper SS, Acosta PB Effect of simultaneous ingestion of L-amino acids and whole protein on plasma amino acid and urea nitrogen concentrations in humans. J Parenter Enteral Nutr, 1991, 15 48−53
Gropper SS, Smith JL Advanced Nutrition and Human Metabolism. California, USA: Wadsworth Cengage Learning, 2013, pp. 183−244.
van Rijn G, Carbasius Weber E. Dieet bij metabole ziekten 1st Ed. WKZ/UMCU Utrecht. 2011:24-38.

PKU: Diet prescription