Die Bedeutung der „lebenslangen Diät“ verstehen

Aminosäuren sind die Bausteine von Eiweiß. Nach der Aufnahme wird Eiweiß von Enzymen in Aminosäuren aufgespalten (von denen es etwa 20 unterschiedliche gibt). Aminosäuren werden für verschiedenste Funktionen des Körpers benötigt, wie z.B. den Muskelerhalt, das Wachstum, die Reparatur von Zellen und Gewebe sowie die Zusammensetzung anderer Körpereiweiße und Aminosäuren.

Phe ist in allen eiweißhaltigen Lebensmitteln enthalten. Bei PKU reichert sich Phe an, weil das Enzym Phenylalaninhydroxylase (PAH) fehlt. Dieses Enzym hilft, Phe in eine andere Aminosäure umzuwandeln: in Tyrosin. Dies führt zu einer Anreicherung von Phe und niedrigen Tyrosinwerten.

Beide Aminosäuren spielen eine wichtige Rolle im Körper. PKU kann von Person zu Person unterschiedlich sein. Manche Menschen haben keine oder nur eine sehr geringe PAH-Enzymaktivität – dies nennt man klassische oder schwere PKU. Manche Menschen haben eine höhere PAH-Enzymaktivität – das nennt man dann mittelschwere oder leichte PKU. Im Falle der leichten PKU wird manchmal der Begriff „Hyperphenylalaninämie“ verwendet (kurz HPA).

Over the last 40 years, recommendations for the management of PKU have changed as experts in the field collect more evidence on the effect of phe levels on health.

In Europe, a group of experts produced PKU management guidelines in 2017 recommending ‘treatment for life’ for people with PKU. Although some adults say they don’t feel any different when they have high phe levels, others do report problems when their phe levels are high. There is also a lot of uncertainty over the long-term effects of high phe levels. The oldest individuals to be diagnosed through newborn screening are now in their 50s and the impact of high levels of phe on aging are not known. As there is currently no strong evidence that it is safe to discontinue dietary treatment in adults, the experts recommended treatment for life.

This means continuing a low protein diet lifelong, that restricts phe, alongside a protein substitute. When following a low protein diet, taking protein substitutes is essential to ensure that you keep your phe levels within the recommended range, maintain lean muscle mass and do not develop nutritional deficiencies.

• Some relax their dietary protein restriction and reintroduce protein-rich foods such as meat, fish and beans but continue to take their protein substitute
• Others may continue to follow a restricted protein diet but do not take protein substitutes
• Some may completely abandon their diet and eat a “normal” diet containing foods that are naturally high in protein such as eggs and meat and no longer take a protein substitute.

The recommendation is diet for life and any changes to your diet should be discussed with your Specialist Metabolic team. If you are struggling to comply with your low protein diet, your metabolic team are a point of call to support you.

If you were to stop taking your protein substitute whilst remaining on a severely restricted protein intake, you will be putting yourself at risk of protein malnutrition and vitamin and mineral deficiencies. This will also lead to high phe levels.

The effects of being “off diet” can vary for each person but will result in high phe levels.

Research has shown that some adults who stop low protein diet can develop symptoms within only a few weeks after discontinuation. You will hear people referring to a feeling of brain fog when phe levels are high. This may affect how well you make decisions such as when you’re driving a car, operating machinery, or performing day to day tasks. Some people report not feeling any effects when they have high phe levels, although it is still unknown what the long-term effects of living with high phe levels may be.

Other possible risks associated with high phe levels may include:

• depression, anxiety
• tremors (the shakes)
• stiff or weak legs
• headaches
• eczema

The current European guidelines recommend blood phe levels below 600 μmol/l, ideally in the range 120 – 600 μmol/l. If you are a female, you need to be aware your phe levels need to be under stricter control during both before you become pregnant (pre-conception) and pregnancy. Your specialist metabolic team will advise on this as these can differ from centre to centre and person to person. For more information on PKU and pregnancy, click here.

Many adults may not be currently following the ‘treatment/diet for life’ approach or even realise that they should be following this as they may have been told as a teenager they no longer needed to follow a diet and therefore have not been seen by a metabolic team for a while.

However, it is never too late to return to a low protein diet, research is showing that re-starting a low protein diet may improve associated risks.

Some people with PKU who have stopped their low-protein diet and then restarted it report when back on their low protein diet that they:

• feel better
• look better
• can think more clearly
• are less moody
• find it easier to get along with others
• feel less tired and have more energy
• can concentrate
• can work things out better, e.g. when trying to think strategically such as in team sports or at work.

• More choice, availability and better tasting protein substitutes and low protein foods
• clinics specifically for adults
• social media provides access to others with PKU
• more accessible options for eating out, e.g. vegan options.
• More options of low protein foods in supermarkets with the increase in coeliac and vegan food options.

When returning to diet, there are certain things to take into consideration such as:

• Aiming to keep within your daily phe target you will be set by your metabolic team
• Taking your recommended protein substitute regularly throughout the day
• Monitoring your phe levels
• Ensuring you have enough of your PKU supplies in stock

Your metabolic team will help you return to a low protein diet. If it has been a long time since you saw your metabolic team, ask your GP to refer you to your nearest metabolic centre to help you get started on a low protein diet. For more information see the Returning To Diet.