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Home > Vitafriendspku > Your pku journey > Practical Tips (Teens)

Practical Tips (Teens)

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Even though you have lived with PKU your whole life, you may be starting to take more of an active role in managing your diet as you’re getting older. You might be starting high school, going off to university or even moving out of the family home. But don’t worry, you are not alone. Here are some practical tips for managing your PKU and if you have any specific questions about your low protein diet, your dietitian will always be happy to help.

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Blood Spots for Phe Monitoring
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Dried blood spots

Providing dried blood spots for Phenylalanine (Phe) monitoring is essential in PKU, as this enables your dietitian to check your phe levels are within a target range and make any amendments needed to your diet. Your dietitian will advise you on how often blood spots need to be provided for testing.

It is important that you become used to providing good quality blood spots. If poor quality blood spots are received at the lab, they may not be accepted.


What are blood spot samples?


Blood spot samples are a drop of blood, about a centimetre in width, that are placed onto a specially made testing card.

This testing card takes 4 blood spot samples and is sent back to a lab where the phe level in the blood is tested.


How do I complete a blood spot card?

Before taking the blood spot sample, check the date on the testing card to make sure it has not expired and that all sections are completed.

These cards may already have a label on them with all your details (it’s still always useful to double check these are correct).

If not, you will need to add them to the card.

Providing a good quality blood spot sample

You will have completed a blood spot sample hundreds of times in your life but just in case you need a refresher on how to do it, here is a step-by-step guide to providing a good quality blood spot sample:

  1. Wash your hands.
  2. Prick your finger.
  3. Allow a drop of blood to form.
  4. Place the blood spot card up to the drop and allow it to drip onto the circle on the card, as close to the centre as possible. Do not press your finger against the card.
  5. Repeat step 4 onto the other 3 circles on the blood spot card.
  6. Once you have finished, cover the prick site with a little cotton wool and light pressure – bleeding should stop almost immediately.
  7. Allow the blood spots to absorb into the card and air dry enough so they lose the initial wet look before putting the card into the envelope provided (if they are not air dry then they can stick to the inside and damage the card).
  8. Send the blood spot sample card back to the hospital as soon as possible once you have completed it. This helps to make sure any changes to your diet can be identified quickly by your dietitian.

Important points to remember

  • Have all the equipment ready before you start.
  • Always take the blood spot sample at the time of day your dietitian has advised but it is usually best to measure early in the morning before the first meal of the day.
  • Blood spots need to be taken from just 1 drop of blood, measuring 0.7cm – this is just under a centimetre in diameter.
  • If blood spots don’t meet this measurement and are taken from more than one drop of blood (overlapping on the card) the phe level result will not be accurate and will need to be repeated.
  • Blood needs to be soaked right through the card so the lab can test it properly.
  • If you have any questions at all about this process, contact your dietitian or the metabolic nurse at your hospital.


Top Tips:


  • Practice makes perfect.
  • Keep your finger below the level of your heart to encourage blood flow.
  • Make sure there is a collection from your post box on the day you post your results.
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Reading food labels
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When you have PKU it is particularly important to know how to read food labels.

This will enable you to check the protein content of foods and work out if the food is suitable for your diet without counting it as a phe exchange.

If you are not used to doing this yourself, this might seem confusing and overwhelming at first, but with practice this should become easier.

As a reminder, the protein in food is counted as phe exchanges. 1 phe exchange is the amount of food that provides 1g of protein.

1g of protein = 50mg of phe

So, 50mg of phe = 1 phe exchange

Most pre-packed foods have nutritional information on the packaging.

Here is an example of the nutritional information on a Weetabix cereal packet:

This label provides information on energy content expressed as kilojoules (kJ) and calories (kcal). Information is also provided on the typical fat, carbohydrate and most importantly for PKU, protein content. All nutritional information is provided per 100 grams and sometimes per portion of the food. So, in this instance 2 biscuits of Weetabix contain 4.5g of protein.

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How To Read Food Labels
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Unless a food is a specially manufactured low protein food, then it is extremely unlikely that the phe content will be provided on a food label.

Sometimes food labels will state that the product contains protein. However, the ingredients list may be made up of foods which you know are exchange free. If this is the case, the food can be eaten without contributing towards phe exchanges.

However, the phe content can be estimated from the protein content. From this, the number of phe exchanges in a certain quantity of food can be calculated.

To work out if a food needs to be counted as a phe exchange look at the protein content on the label. If the protein is 0.5g or less per 100g, then this food is classed as exchange free (please note, this does not apply to plant-based alternatives to milk, please speak to your dietitian about this). However, if it is over 0.5g per 100g, then you will need to calculate how much of that food is a phe exchange. Your dietitian will tell you how many phe exchanges are allowed each day.

The National Society of Phenylketonuria (NSPKU) dietary information booklet provides a comprehensive list of products which are exchange free. For further information, visit

Calculating phe exchanges

When you know the protein content of a food per 100g, you can calculate how much of that food equals 1 phe exchange.

For example, this yoghurt contains:

5.1g of protein per 100g. So 100 ÷ 5.1 = 20g. Therefore, 20g is equal to 1 phe exchange.

When you need to calculate phe exchanges quickly, print off and use the ready reckoner below.

For example, if the protein content on the label states 0.9g per 100g, then 111g of this food is counted as 1 phe exchange.

Exchanges Table
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Phe exchanges per portion of food
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Usually, it will say on the label how much protein there is in 1 portion. The table below shows how many phe exchanges are in a portion of food based on the protein content.

If a portion of food contains 0.3g protein or less, it is exchange-free for 1 portion. However, if you eat more than 1 portion it will need to be counted towards your daily exchange allowance as advised by your dietitian.

Small Exchanges Table

If you do not have the protein content per portion available, then you can still work out the number of exchanges per portion of food using the steps below:

  1. Multiply the protein content of food per 100g by the amount of the food eaten.
  2. Divide this number by 100 to give the number of phe exchanges per portion of food.
Calculating Phe Label

If you eat 20g of yoghurt:

5.1 (protein per 100g) x 20 (amount eaten) ÷ 100 = 1 phe exchange.

Remember practice makes perfect and will increase your confidence in working out what you can incorporate into your low protein diet.

We recommend you regularly refer to the NSPKU dietary information booklet on their website for the most up-to-date nutritional information.

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Cooking With Low Protein Foods

As your independence grows and you start to gain confidence in the kitchen, you may start to increase variety in your meals. Specially manufactured low protein foods will become staples of your diet, if they aren’t already, and act as a great base to build a meal around. Here are a few helpful hints and tips for cooking with specially manufactured low protein foods:

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Low protein pasta

  • Make sure the water is boiling rapidly with a little oil in to keep the pasta from sticking together whilst it’s cooking.
  • Stir constantly for the first 2 minutes when the pasta goes into the boiling water.
  • Always rinse the pasta in cold water after cooking to remove the starch and stop it sticking together.
  • If you want to eat it hot, warm the sauce and add the cooled pasta to it.
  • Cooked pasta can be placed in a zip lock bag with a teaspoon of oil to prevent it sticking together. This can be stored in the fridge then microwaved on high for one minute in the zip lock bag to let the steam refresh it before eating. It’s recommended to eat within 2 days of cooking.
  • Low protein lasagne sheets work best if you soak the sheets in warm water, with a teaspoon of oil, for 5 minutes before making up the lasagne.
  • If you run out of low protein pasta before your next delivery, you can use pasta alternatives such as spiralised courgette, butternut squash or carrot.
  • Or you can make your own sweet potato gnocchi or ravioli at home!
  • You could use vegetables like sliced butternut squash instead of low protein pasta sheets in lasagne if you have run out.

Low protein rice

  • Make sure the water is boiling rapidly with a little oil in to keep the rice from sticking together whilst it’s cooking.
  • Stir constantly with a whisk/fork for the first 3-4 minutes when the rice goes into the boiling water.
  • Cook for no longer than 9 minutes. Always rinse the rice in cold water after cooking to remove the starch and stop it sticking together.
  • Rice can be coloured and flavoured by adding ½ teaspoon of turmeric or tomato purée into the water when cooking.
  • You can make ‘rice’ out of sturdy vegetables such as carrots, beetroot, squash and sweet potatoes. Just grate them and pop them in the food processor and blitz to a rice-like texture. Then microwave for 1-2 minutes or until soft.

To bake low protein bread

  • When baking bread, adding psyllium husk to the recipe creates a spongy texture and makes it last longer. For a delicious low protein bread recipe, click here!
  • Warm (but not hot) water is required to activate the dried yeast in low protein bread recipes. Store in a zip lock bag to freeze.
  • A loaf of bread, if placed in an airtight container, will last for about a week (the bread will dry out quicker than this if there is no psyllium husk used in the recipe).
  • If required, refresh slices of bread by microwaving for 10 seconds in between pieces of kitchen roll.
  • Adding herbs and spices to the dough creates flavoured bread e.g. dried basil, thyme or oregano. Bread machines make good low protein bread – just follow the manufacturer’s instructions.

To bake low protein cakes

  • Brown sugar (not demerara) creates a moister texture than white sugar.
  • Lemon or orange juice helps to flavour and colour cakes.
  • Permitted fruit added into cakes provides texture and variety.

Additional useful tips:

  • Vegetable soups freeze and keep well.
  • Don’t freeze cooked spiralized veg – it won’t freeze well and will be soggy when defrosted/cooked.
  • Batch cook lasagne, Bolognese sauce and ratatouille to have ready-made meals in advance.
  • Frozen low protein food keeps about the same length of time as equivalent non-low protein frozen food.
  • Make sure dishes are wrapped and protected well in the fridge/freezer to keep them at their best.
  • Remember to label and date foods when freezing.
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