An investigation into diet treatment for adults with previously untreated phenylketonuria and severe intellectual disability.

Doctors gave five adults with severe intellectual disability a low-phenylalanine diet. All five had never been treated for PKU. Staff watched mood, alertness, and daily living skills for several months.

Four of the five adults woke up faster, stayed calmer, and learned more daily tasks. Irritability dropped and smiles increased. The team called the diet safe and worth trying.

Raslear et al. (1992) and Einfeld et al. (1995) ran single-case tests first; Bailey et al. (2000) now adds more adults and firmer yes.

Hatton et al. (1999) tracked the same UK group and found the diet also saved £20k per person in nursing hours.

Katz et al. (2003) seems to clash: restricted diets left autistic kids low in other amino acids. The gap is metabolic need—PKU brains poison themselves on phenylalanine, autism brains do not.

If you serve adults with severe ID and untreated PKU, ask the doctor about a low-phenylalanine diet. It may cut aggression, boost eye contact, and lower care costs. Track mood, self-care, and nursing time for six weeks; small gains can justify the kitchen effort.