As an adult with PKU you may have been told as a child or a teenager that you no longer needed to follow a low protein diet. This is because, it used to be thought that high blood phe levels had minimal impact once the brain was fully developed and it was thought the brain was fully developed once you were a teenager. However more recent research and findings has led to the recommendation of Diet for Life.
Although some adults say they don’t feel any different to their norm when they have high phe levels, others do report problems when their phe levels are high and it is thought that the variability in cognitive outcomes in adults with PKU is linked to the variability in dietary adherence.
Research has shown that cognitive performance is linked with present and past phe levels. It is thought that high phe levels in adulthood have more of an effect on parts of the brain that develop later such as executive function which includes speed of processing and the ability to sustain attention. You will hear people referring to a feeling of ‘brain fog’ when phe levels are high. You may feel a bit muddled when doing tasks and your friends, family and colleagues may notice you’re not quite yourself. Having a poor executive function may hinder you when you’ve got a packed schedule or if you are starting a new job.
Newborn screening for PKU has now been possible for over 50 years and this means that the oldest individuals treated for PKU from birth are into their 50’s. However, the effects of high phe long term are not fully known and the potential effects on ageing will continue to be studied.
As previously stated, there is currently no strong evidence that it is safe to discontinue dietary management in adulthood, the experts recommended treatment for life.
Possible long-term risks associated with high phe levels may include:
Unplanned pregnancies are common. However, high blood phe in a mother with PKU can have devastating effects on the unborn baby, so it is important blood phe levels are controlled prior to becoming pregnant. See PKU and Pregnancy for more information.
High phe levels do not tend to occur in isolation. If an individual has high phe levels due to no longer taking their protein substitute as part of their diet, they are also at risk of not fully meeting their requirements for several vitamins that are added to the protein substitute.
The recommendation is Diet for Life but if an adult feels very strongly that they want to come off diet, they should discuss it with their Specialist Metabolic team. Although the team will respect and seek to support that individual’s choice, they will also want to monitor their health and well-being to ensure that coming “off diet” has no ill effects. Part of that monitoring will be ensuring that the diet is well balanced and providing all the nutrients required for good health.
If somebody simply stops taking their protein substitute whilst remaining on a severely restricted protein intake, they are putting themselves at risk of protein malnutrition and vitamin and mineral deficiencies.