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Home > Vitafriendspku > Your pku journey > What Factors Effect Phe Levels? (Teens)

What Factors Effect Phe Levels? (Teens)

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

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What to do if I am unwell?
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When you are unwell, your energy (calorie) needs automatically increase as your body tries to fight the illness. 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.  

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Physical Activity and Exercise
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There is nothing stopping you from being active or competing in a sport of your choice. A sedentary lifestyle can be harmful to your health, so physical activity is encouraged wherever possible and through all life stages. 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. 


For more information on PKU and exercise see Physical Activity and Exercise. 

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Growth during the teenage years and rapid weight loss
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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. 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 is more detail at your clinic appointments. 

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Eating too much of certain types of food can also affect your blood phe levels. Too many phe exchanges will lead to a rise in your blood phe. It is important that you are aware of foods that naturally contain protein.  For more information on a balanced diet and healthy eating with PKU see Healthy Eating.  

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Learn more about PKU

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