'Ready to drink' protein substitute is easier is for people with phenylketonuria

J Inherit Metab Dis. 2006 Aug;29(4):526-31. doi: 10.1007/s10545-006-0234-y. Epub 2006 May 30.


In phenylketonuria (PKU), compliance with taking protein substitute is an issue in teenage and older patients. A 'ready to drink' protein substitute may overcome many of the practical issues associated with its administration.

Objective: To investigate the efficacy of a liquid protein substitute in a 6-week, three-part, randomized, crossover, controlled study.

Methods: 27 subjects (15 female; 12 male) with PKU with a median age of 30 years (range 8-49 years) were recruited. One subject withdrew from the study. Their median daily dose of protein equivalent was 60 g (range 45-75 g). In parts 1 and 2, subjects were randomized to either a liquid or a powder protein substitute with the same nutritional composition per unit (each 130 ml liquid pouch or 25 g powder sachet contained 15 g protein equivalent). In part 3, subjects chose liquid, powder or a combination of both. Weekly blood phenylalanine (Phe) concentrations were estimated, and during weeks 2, 4 and 6 subjects completed a daily questionnaire on administration issues.

Results: All but one of 26 subjects chose the liquid in part 3 as either their sole (69%, n = 18) or partial source (28%, n = 7) of protein substitute. Blood Phe concentrations were significantly better on the liquid (p = 0.03). With the liquid protein substitute, subjects were less self-consciousness (p = 0.003) and found it easier to take away from home (p = 0.001). Overall, the liquid was easier (p < 0.0001), more convenient (p = 0.002) and resulted in less wastage of protein substitute (p = 0.001).

Conclusion: Liquid protein substitute was popular and efficacious, reduced self-consciousness and overall improved compliance of teenagers and adults with PKU.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adolescent
  • Adult
  • Beverages
  • Child
  • Cross-Over Studies
  • Diet*
  • Dietary Supplements*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Phenylalanine / blood*
  • Phenylalanine / chemistry
  • Phenylketonurias / therapy*
  • Proteins / chemistry
  • Tyrosine / blood*
  • Tyrosine / chemistry


  • Proteins
  • Tyrosine
  • Phenylalanine