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Home > Vitafriendspku > Your pku journey > What Factors Affect Phe Levels? (Children)

What Factors Affect Phe Levels? (Children)


There are many different factors that can affect phe levels. Your dietitian will be able to give you guidance on these, so you will know what to expect.

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They can include things like your child being unwell, not eating enough, eating too much or too little protein and not taking their protein substitute as prescribed.

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My child is unwell

It is normal for children to suffer with common childhood illnesses like coughs, colds or high temperatures.  If your child is unwell, encourage fluids and energy (via fluids and easy to eat foods).

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Ensuring they stay hydrated and take in enough energy (calories), so they have the energy to fight the illness and minimise protein breakdown is important. If your child doesn’t eat enough energy (calories), then like everyone, their bodies will break down the protein stores from their muscles to use for energy. This means amino acids, including phe, will be released into the bloodstream and blood phe levels will increase. It is important to contact your GP and dietitian for advice.  

If your child must take medication when they are ill, remember, some medications contain aspartame, which is a source of phe, and these must be avoided (unless your doctor tells you otherwise). Always check the ingredients of medications with your dietitian or pharmacist.

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My Child Is Not Eating Enough

If your child is gaining weight and growing well you know they are eating enough. If children are losing weight or not gaining then they need to eat more calories (energy).

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It is important that your child manages to meet their daily protein needs from consuming natural protein from foods (counted as your child’s protein allowance) , phe-free protein provided by a protein substitute and overall sufficient energy to meet their needs. The amount of natural protein allowed, protein substitute needed and total calories is different for each child and is monitored and advised by your dietitian.  

If your child is very active they will need more calories overall. It’s important that enough energy (calories) are consumed to meet their activity levels. If not, then like everyone, the body breaks down its protein stores from the muscles to use for energy. This means their blood phe levels will increase. Discuss with your dietitian if you are worried that your child is not eating enough.

Eating a varied and balanced diet that contains protein-free foods like permitted fruits and vegetables, low protein specially manufactured foods, natural protein to meet their protein allowance and their protein substitute, as well as some fats and sugar, will help your child meet their daily energy (calorie) needs. 

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My child is eating too much or too little protein

Eating too much or not enough protein as advised by your dietitian can affect blood phe levels.

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Try to measure and count intake of protein and involve your child where appropriate. You may find it helpful to write this down to keep a close eye on what’s being consumed. Aim to speak to your child calmly about what they are eating and when, and speak to any relevant caregivers, to help understand what is going on and to see if there are times when food is or isn’t being eaten.

It is important to work with your child so they feel supported and not threatened that they are in trouble. Once you have a good idea what is going on try to be consistent with your child’s protein intake and monitor blood phe levels. Discuss with your dietitian to finetune any changes required.

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My Child Is Refusing To Take Their Protein Substitute

If your child is not taking their protein substitute, talk to them and try to understand why. There are many reasons why a child will not take their protein substitute and it may be an easy fix. If your child’s concerns are listened to they will feel supported. If it is because they dislike their current protein substitute, speak to your child’s dietitian and ask if there are alternatives to try. This way, your child can feel some control in choosing what protein substitute they will carry on taking. 

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Whilst waiting to try or receive a new protein substitute, explain to your child why they must continue to take their current protein substitute in the meantime. Try to discuss it in terms that your child will understand and what is important to them. Talk to them about what a protein substitute is and its importance, in case they have forgotten. Explain to your child that their concentration in school and ability to do their schoolwork may be affected if they do not take it. If they take part in sports, letting them know their energy levels and performance may suffer could encourage them to make sure they take their protein substitute.   

It could be that they are feeling self-conscious taking their protein substitute in front of their school friends. If this is the case, contact the school and arrange for your child to be able to take it in private – maybe in the school office away from other pupils. If your child agrees, it could be useful to ask the teacher to explain to the class why it is important that your child takes their protein substitute.   

When talking with your child try to uncover their concerns or what they don’t like about their protein substitute and work with them to find a solution to ensure there is minimal disruption to them actually taking it. If you need further help and support speak with your metabolic clinic. Other families and children with PKU may be helpful too so don’t be shy to ask and reach out for help.

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