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Dietitians are involved in treating patients with long-term conditions, and long-term conditions are associated with a mental health burden.1 Phenylketonuria (PKU) is no exception.2 In this unusual year, more than ever before, it may be useful to be aware of mental health issues and resources available to help patients and nutrition professionals alike, says Suzanne Ford, Society Dietitian with the NSPKU.

Physical health and physical activity can be a challenge too, and the link between mental health and physical health are clearly evidenced.3 The information and resources available online need not just be for patients but could be relevant to dietitians’ self-care as well.


People with PKU are particularly vulnerable to poor mental health due to the raised phenylalanine and toxicity – this is hypothesised to cause neurotransmitter disruption. People with PKU cannot breakdown the amino acid phenylalanine and convert it into tyrosine. Due to the higher uptake of phenylalanine into the brain 4 and potentially low tyrosine levels,5 the alterations in brain chemistry are thought to lead to prefrontal cortex dysfunction. The prefrontal cortex helps in emotional stability.6,7

There is evidence that taking protein substitutes, which contain high levels of large neutral amino acids, reduce the uptake of phenylalanine to the brain and further improve functioning when combined with a low phenylalanine diet.8 For people with PKU, being on dietary treatment is highly likely to improve mental health.9 There is also evidence that poor mental health is not in the person experiencing effects of high phenylalanine, but all who live with it, with 59% of caregivers of children with PKU experiencing clinical levels of psychological distress.10


This year, it has been recognised and evidenced that the ‘invisible enemy’ of COVID-19 and changes to our way of life have caused an increase in poor mental health.11 Many readers of this article, who work for the NHS, may already know about the following websites with trusted mental health advice – however, they are worth sharing widely:


Activity levels may be reduced due to restrictions on our lives imposed by lockdown. However, weight control and physical activity are more important than ever before. Furthermore, being active is a key part of mental health too.

The UK recommendations for activity for 19 to 64-year-olds – first published in 2011 and updated as recently as January 202012 – are as follows:

  1. All adults aged 19 years and over should aim to be active daily.
  2. Over a week, this should add up to at least 150 minutes (2.5 hours) of moderate intensity physical activity in bouts of 10 minutes or more.
  3. Alternatively, comparable benefits can be achieved through 75 minutes of vigorous intensity activity spread across the week or combinations of moderate and vigorous intensity activity.
  4. All adults should also undertake physical activity to improve muscle strength on at least two days a week.
  5. They should minimise the amount of time spent being sedentary (sitting) for extended periods.

A great resource is the Public and Patient part of the website run by the Chartered Society of Physiotherapists for its pages entitled Keeping active and healthy, which has subsections on Staying Active at Home and Working from Home, How to Get More Active and Love Activity, Hate Exercise? All can be found here: https://www.csp.org.uk/public-patient/keeping-active-healthy


How many of us promote physical activity to our patients with long-term conditions, as a means of staying both physically and mentally healthy? And would we read this and use the material for ourselves?

Self-care for dietitians is important – modelling healthy lifestyle choices, not just signposting towards them, will help us remain healthy and effective healthcare professionals.

In summary, lockdown requires holistic dietetic interventions to consider all aspects of patient wellbeing.


Suzanne Ford
Society Dietitian for

National Society for Phenylketonuria
Specialist Dietitian, North Bristol NHS Trust


  1. Demain S et al (2015). Living with, Managing and Minimising Treatment Burden in Long-Term Conditions: A Systematic Review of Qualitative Research. PLoS ONE 10(5): e0125457. https://doi.org/10.1371/journal.pone.012545
  2. Moyle J, Fox A, Arthur M, et al. Meta-analysis of neuropsychological symptoms of adolescents and adults with PKU. Neuropsychology Review. 2007; 17(2): 91-101
  3. Biddle S. Physical activity and mental health: evidence is growing. World Psychiatry. 2016; 15(2): 176-177. doi:10.1002/wps.20331 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4911759/
  4. Pardridge WM. Blood-brain barrier carrier-mediated transport and brain metabolism of amino acids. Neurochemical Research. 1998; 23(5): 635-44
  5. Smith QR, Momma S, Aoyagi M et al. Kinetics of neutral amino acid transport across the blood‐brain barrier. Journal of Neurochemistry. 1987; 49(5): 1651-8
  6. Anwar M, Waddell B, O'Riordan J. Neurological improvement following reinstitution of a low phenylalanine diet after 20 years in established phenylketonuria. BMJ case reports. 2013; bcr2013010509
  7. Daelman L, Sedel F, Tourbah A. Progressive neuropsychiatric manifestations of phenylketonuria in adulthood. Revue Neurologique. 2014; 170(4): 280-7
  8. Broer S. Amino acid transport across mammalian intestinal and renal epithelia. Physiological Reviews. 2008; 88(1): 249-86
  9. Pietz J, Kreis R, Rupp A et al. Large neutral amino acids block phenylalanine transport into brain tissue in patients with phenylketonuria. The Journal of Clinical Investigation. 1999; 103(8): 1169-78
  10. Medford E, Hare DJ, Carpenter K, Rust S, Jones S, Wittkowski A. Treatment Adherence and Psychological Wellbeing in Maternal Carers of Children with Phenylketonuria (PKU). JIMD Rep. 2017; 37: 107-114. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5740045/
  11. Pierce M et al. Mental health before and during the COVID-19 pandemic: a longitudinal probability sample survey of the UK population; The Lancet Psychiatry; Volume 7, Issue 10, October 2020, Pages 883-892.
  12. https://www.gov.uk/government/publications/physical-activity-guidelines-uk-chief-medical-officers-report









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