Low protein diet
A low protein diet is the main type of treatment for phenylketonuria (PKU).
Your dietician will be able to draw up a detailed dietary plan for your child and they will also be able to help revise the plan over time as your child gets older and their needs change.
It is beyond the scope of this article to provide a complete overview of all the recommendations and information regarding low protein diets. For more detailed information and advice, the National Society for Phenylketonuria (NSPKU) website has a section that provides dietary information. The NSPKU is the UK’s leading charity for people with PKU.
In general terms, the NSPKU recommend a ‘traffic light’ approach to diet where foods are categorised as follows:
- green foods - are those that are safe to eat because they contain very low levels of protein, although they should not be eaten to excess
- amber foods - contain protein and must be carefully weighed; they will be eaten in different quantities according to your blood phenylalanine level
- red foods - should never be eaten under any circumstances
Below are examples of green, amber and red foods.
Green foods
Examples of green foods include:
- fresh fruit with the exception of bananas, figs and dates
- most vegetables with the exception of asparagus, bean sprouts, broccoli, Brussels sprouts and cauliflower
There are also a number of specially designed low protein versions of popular products, such as flour, rice and pasta that are specifically designed for people with PKU and related conditions. Many of these special foods are available on prescription so you will not have to pay the full price for them.
Amber foods
Examples of amber foods include:
- cornflakes
- chips
- baked beans
- milk - a specially designed formula can be used as a milk substitute for babies and children
- normal rice
Red foods
Examples of red foods include:
- all types of meat
- eggs
- fish
- cheese
- beer - lager and bitter
- any food that has been baked using flour, such as bread
Dietary Supplements
As well as sticking to a low protein diet, people with PKU will also have to take regular dietary supplements. These contain all the essential nutrients that are absent from the low protein diet. The supplements contain a mixture of all the amino acids (apart from phenylalanine) that are essential for the body to grow and remain healthy. Supplements are available in various different forms, including powders, drinks and tablets and need to be taken three or four times a day.
Aspartame
People with PKU also have to avoid food products that contain aspartame. Aspartame is an artificial sweetener that can be found in:
- sugar substitutes, such as artificial sweeteners that are often used in tea and coffee
- diet versions of fizzy drinks
- chewing gum
- squashes and cordials
- some alcopops
All food products that contain aspartame or a related product should state on the packet ‘contains a source of phenylalanine’.
There are also a number of medications that contain aspartame, such as some cold and flu remedies for children. It is a legal requirement for any medication that contains aspartame to state it on the patient information leaflet that comes with the medication.
You should always make sure you read the patient information leaflet carefully before giving any medication to your child.
Sapropterin
Sapropterin is a new type of medication that has proved to be effective at reducing the level of phenylalanine in some children and adults with PKU. Sapropterin is a synthetic form of a vitamin which helps the PAH enzyme to work better. However, sapropterin only works for some types of PKU, depending on precisely which PAH gene mutation is present.
Sapropterin is available in tablet form. The amount of tablets your child will need to take will depend on their body weight - the more they weigh, the more tablets they will require. A person with PKU who is treated with sapropterin may be able to relax their diet, although it is unlikely that they will be able to eat normally.
Sapropterin is a very expensive medication; it costs more than £100,000 a year to treat an adult. As PKU is a very rare condition, the National Institute of Health and Clinical Excellence (NICE) is not going to make any recommendations about its use in the NHS. This means that it is up to individual local primary care trusts (PCTs) to decide whether to use sapropterin.
Due to the high cost of sapropterin, the fact that it is only effective in a small number of patients and the fact that diet is such an effective treatment for PKU, it is currently very unusual for someone in the UK with PKU to be treated with sapropterin.
