The use of a low phenylalanine diet with amino acid supplement in the treatment of behavioural problems in a severely mentally retarded adult female with phenylketonuria.

Doctors gave one adult woman with severe intellectual disability and untreated PKU a special low-protein diet for 18 weeks. They also gave her an amino-acid drink to replace the protein she could not eat.

Staff watched her behavior every day and wrote down how often she hit, screamed, or hurt herself.

The woman’s serious behavior problems dropped clearly while she stayed on the diet. When phenylalanine levels fell, she was calmer and needed fewer restraints.

Bailey et al. (2000) later tested the same diet on five adults and saw better mood and alertness in four of them. This larger group adds weight to the 1992 single-case result.

Hatton et al. (1999) tracked money, not just behavior. They found the diet saved about £20,000 per patient in one year because nurses spent less time managing outbursts.

Einfeld et al. (1995) looks like a contradiction at first. Their adult man showed only small, unclear gains. The catch: he started new medicines at the same time, muddying the picture. When you remove that drug confound, the diet effect lines up with Raslear et al. (1992).

If you serve adults with severe ID and untreated PKU, a low-phenylalanine diet is a low-tech, side-effect-free tool that can cut aggression and self-injury. Pair it with close blood testing and amino-acid support. The same plan can also shrink care costs and may boost alertness for day-program work tasks.