Sorry, you need to enable JavaScript to visit this website.
Change language
Home > Vitafriendspku > Your pku journey > What Factors Effect Phe Levels? (Teens)

What Factors Effect Phe Levels? (Teens)


Having PKU should not prevent you from gaining or maintaining excellent general health.

Read more

As with the rest of the population, eating a healthy varied diet, enjoying good quality sleep and staying physically active, all have a part to play in this. However, if you have PKU, an additional consideration is keeping your phe levels within the target range recommended for you.  


Knowing what can affect your phe levels can help you understand how to cope with levels if they change. Some of the factors that might affect your phe levels include:  


  • Being unwell 

  • Physical activity and undereating 

  • Rapid weight loss 

  • Hormonal changes e.g. puberty, the menstrual cycle and early stages of pregnancy 

  • Overeating on dietary protein and not taking your protein substitute as prescribed. 


Your metabolic team will be able to give you more guidance on these, so you will know what to expect. 

Read less
What to do if I am unwell?

When you are unwell, your energy (calorie) needs automatically increase as your body tries to fight the illness.

Read more

You might also find that your appetite is reduced. These two factors combined can result in your body breaking down its protein stores from the muscles to use for energy. This breakdown of protein in your muscles releases phe into the blood causing phe levels to increase. 


It is important that you to contact your metabolic team or GP if you are unwell and struggling to eat and drink enough.  


If you must take medication when unwell, remember, some medications contain aspartame, which is a source of phe and must be avoided (unless your doctor or metabolic team tells you otherwise). Always check the ingredients of medications with your metabolic team or pharmacist before taking.  

Here are some suggestions on how to minimise the rise in your phe levels during illness: 

  • Try to eat small frequent meals as tolerated to ensure adequate energy (calorie) intake.  

  • Aim to take your protein substitute as normal. If you’re unable to do so, make sure you contact your metabolic team promptly. 

  • Consider your phe exchanges. Your metabolic team may advise you to cut back on phe exchanges if phe levels are raised. You might find that this will have happened naturally as appetite may be reduced during illness.  

  • Stay hydrated. Ensure adequate fluids are taken especially if symptoms include vomiting and/or diarrhoea. 

  • Check for suitable medication. Look out for aspartame and seek the guidance of your pharmacist or metabolic team if you’re unsure. It is also important not to mix any medications, such as antibiotics, into the protein substitute as this will alter the taste and consistency.  

Read less
Physical Activity and Exercise

Being physically active such as playing a sport of your choice is encouraged for overall fitness, strength, wellness and general health.

Read more

A sedentary lifestyle can be harmful to your health, so physical activity is encouraged wherever possible and through all life stages. Aim to make physical activity part of your week, and ideally most days participate in some kind of exercise. One of the many benefits of regular exercise (or manual labour) is that your body will use protein to build muscle. Phe, as an amino acid, is a building block of protein so the phe from your diet will be used to help build muscle and reduce the amount of phe in your blood. 

Exercise promotes muscle mass and overall strength which is important for everyone. Exercise increases your requirement for energy and can be useful for weight control.  

Some people may be very active and struggle with eating enough calories and maintaining a healthy weight. Regular meals and snacks and having drinks with calories (juice, cordials, sport drinks, low protein milks) will help boost overall calorie intake. Speak to your dietitian for further tips. 

Read less
Growth during the teenage years and rapid weight loss

During the teenage years you will experience periods of rapid growth and hormonal changes as part of puberty. Part of this will involve you building up body mass and muscle.

Read more

Phe is needed along with the other amino acids, vitamins and minerals from your low protein diet and protein substitutes to help you grow. At these times the blood phe level should be measured more frequently because it may be necessary to adjust your protein allowance and therefore phe intake to meet the growing needs of your body. Your body may require more energy (calories) during these growth spurts, so you may find your appetite increases. It is important that you eat enough calories to prevent rapid weight loss and the breakdown of fat and protein from your body’s stores.  

Your metabolic team will explain this in more detail at your clinic appointments. 

Read less

Eating too much of certain types of food can also affect your blood phe levels.

Read more

It is important that you are aware of foods that naturally contain protein. Eating too many calories will cause weight gain. 

Looking closely at your food intake, routine, eating behaviour and habits and exercise pattern will help work out the best way to fine-tune your diet to avoid further unnecessary weight gain. If you are struggling and feel you are gaining too much weight discuss this with your dietitian. 

Undereating protein can cause phe levels to drop too low. Phe is an essential amino acid so it is important you eat enough to meet your body’s needs, but too much that you levels are high. It is a fine balancing act. If your phe levels are too low your dietitian will ask you to increase your intake of natural protein. 

Read less
Protein Substitute

Taking your protein substitute is a vital part of the diet for PKU.

Read more

It provides important amino acids (protein), vitamins and minerals and some energy that is essential for everyday health and wellbeing. As the diet for PKU is so restrictive in natural protein quantity and quality it does not provide sufficient amino acids and vitamins and minerals to meet your body’s requirements. The protein substitute supplements your diet to ensure your body obtains the nutrients it requires.

Without it you are at risk of deficiency and your body will break down your muscle stores releasing phe into your blood, causing levels to be high. Consuming the right amount of protein substitute over the day to meet your requirements is best to keep your phe levels within the normal range. Speak to your dietitian if you are having trouble consuming the amount you need or simply would like an alternate option. There are many to choose from, so there may be a better option for you. 

Read less

Learn more about PKU

< Return to Teens Page