Unrestricted consumption of fruits and vegetables in phenylketonuria: no major impact on metabolic control

Abstract

Background/Objectives: The treatment of phenylketonuria (PKU) requires consistent restriction of protein intake from natural sources. Therefore, protein from all foods has to be accounted for, even the small amounts in fruits and vegetables. We studied whether free consumption of fruits and vegetables containing less than 75 mg phenylalanine (phe) per 100 g affects metabolic control in children with PKU. Subjects/Methods: Fourteen children (2-10 years) were included in a cross-over study, with a two-week period of conventional treatment (accounting for protein from fruits and vegetables) and a two-week period with free fruit and vegetable consumption. The instruction to follow liberal fruit and vegetable consumption in the first or second study period was randomized. Detailed daily dietary records were obtained throughout the study. Phe and nutrient content was calculated. Dried-blood phe concentration was monitored daily. Results: Although total phe intake increased by an average of 58 mg per day (P ¼ 0.037) during the 2 weeks of free fruit and vegetable consumption, dried-blood phe concentrations were unchanged. Total intake of fruits and vegetables did not increase, but patients instead used the higher phe tolerance to consume more of other foods, which were calculated and accounted for. Conclusion: Free consumption of fruits and vegetables does not impair metabolic control in PKU patients over a 2-week period.

Nutritional Changes and Micronutrient Supply in Patients with Phenylketonuria Under Therapy with Tetrahydrobiopterin (BH4)

“…However, a special supplementation of vitamin C seems not to be necessary for PKU patients, as the most fruit and vegetables, the main sources for vitamin C, are low in protein and could be consumed in adequate amounts. Recent studies even showed that free consumption of fruits and vegetables does not impair the metabolic control in PKU patients (MacDonald et al 2003;Rohde et al 2012;Zimmermann et al 2012). Hence, independent from the therapeutic regimes (Phe restricted diet + AAM alone or in combination with BH 4 ) it should be the objective to encourage the patients to eat more fruits as well as vegetables, rather than supplementing vitamin C.…”

“…In the classical treatment of PKU it is necessary to plan meals exactly and to calculate the Phe content of all foods. Only recently, some specialized centres allow the unrestricted consumption of fruits and vegetables under certain conditions (Macdonald et al 2003;Rohde et al 2012;Zimmermann et al 2012). However, the individual Phe tolerance has to be respected.…”

Effect of dietary regime on metabolic control in phenylketonuria: Is exact calculation of phenylalanine intake really necessary?

“…Other studies, although investigating small patient groups, could demonstrate the safety of dietary regimes without exact calculation of Phe from all ingested foods and beverages in children with classical PKU. These include investigations of small cohorts with respect to free use of fruits and vegetables in short-term [9], [11], as well as long-term settings [8], [10], [12]. The regimes 2, 3 and 4 revealed similar results, and in total represent a group of 80 patients.…”

“…Within this system, however, there are differences with respect to its degree of accuracy. So far, only few studies with small patient groups of children and adolescents were performed to examine the influence of dietary regimes on metabolic control [8], [9], [10], [11].…”

“…< 10 mg/100 g food. Dietary regime 3 combines free consumption of low protein foods (< 10 mg Phe/100 g), fruit and vegetables (< 75 mg Phe/100 g) with calculating the exact Phe content of all other foods [9], [10], [11], [12]. Dietary regime 4, the so-called “simplified diet”, consists of estimating the Phe content according to certain principles (free use of five portions of fruit and vegetables; free use of special low protein food including low protein bread, pasta and breakfast cereals; quantities of potatoes, rice and maize are discussed with the parents and then fixed for a period of time) [8].…”