How to help the new PKU person in your life

How to help the new PKU person in your life

It can be scary to hear that someone you have just met has PKU. Whether it’s a new friend, partner, work colleague or whoever they may be to you. Like so many others who are new to the idea of PKU and are curious to learn more about it, the first thing you may do or have already done, is a web search for it. You enter the word “PKU” into google but unfortunately, as with all medical matters when you search for them on the internet, it does not always provide a helpful introduction. The first thing that comes up on my google is the NHS website which has these introductory lines: Phenylketonuria (PKU) is a rare but potentially serious inherited disorder. Our bodies break down the protein in foods, such as meat and fish, into amino acids, which are the “building blocks” of protein. People with PKU cannot break down the amino acid phenylalanine, which then builds up in their blood and brain. This can lead to brain damage*.

But upon reading that, understandably the only words people tend to see are ‘Brain damage’ and ‘Protein’. Knowing protein is something that is in some food, out of curiosity you may start to read the labels of the different food products that you have in the kitchen and then have that sudden realisation that ‘hang on a minute, there is protein in everything!’. So, understanding that you now know someone with PKU, you start to question how on earth you don’t accidently poison your newfound friend! Well, this is the goal of my blog; I hope to shed some light on what PKU is in a more helpful way and give advice on how you can cater for, and maybe provide some support for, this rare condition.

Science stuff

Before we get into the minefield of eating, lets rewind back to what PKU, protein and amino acids are. Naturally, you may think, as the issue is to do with food, that PKU is an allergy but unlike allergies, PKU is not caused by the immune system in our bodies, it’s caused by the metabolic system. As the NHS website has said, amino acids are an essential building block of protein and they can be found in all the foods that when eaten, we metabolise. It’s the amino acids in our food that give us our daily energy, they are how we are able to move, grow and thrive.

Having PKU means that we are missing the ability to break down the essential amino acid phenylalanine (sometimes called Phe), because of this, we get a dangerous amount of Phe in our blood that pumps around to our brain, which is what causes the brain damage described earlier. To control the amount of Phe in our blood, we must control how much Phe we intake, via how much protein we eat. Every single person with PKU is different, we all have different tolerances to protein, some can eat loads and others barely any.

As we must control how much Phe goes into our body, it means most high protein foods are completely taken out of our diet (more on that in a minute), however we do still need to eat certain proteins or there is a risk we will lose out on the other essential amino acids and vitamins that we need to develop. For this we take a protein substitute, there are many different formats depending on age, tolerances, flavour and ease of use. This can come in the form of tablets, drinks or gels, some are taken 3 times a day, others 6 times.

Eating and Drinking

As PKU is not an allergy, we do not have an allergic reaction when we do eat certain foods, whether by accident or on purpose but that doesn’t mean eating those foods is any less dangerous because there is no instant reaction, the long term effects it has on the brain need to be taken just as seriously as any allergy.

The most important thing to remember when it comes to the PKU diet is that in nearly all circumstances we cannot have any high protein items, this includes meat, fish, dairy, wheat, nuts, lentils, pulses, soya, Quorn or tofu. We also cannot have any drinks containing aspartame. Before the sugar tax it was quite easy to tell what drinks had aspartame in them, as generally all full fat options had normal sugar and the diet alternatives would have had the aspartame.

However, with the sugar tax going up, more and more companies are also using aspartame  in their full fat versions, drinks like Dr Pepper, Sprite and most branded squashes. ALWAYS check the label if you are not sure, you will know if it contains aspartame because it will have it in the ingredients and under the ingredients there will be a warning label, that says contains a source of phenylalanine in bold writing. This label has been specifically written for people with PKU as it is so dangerous because essentially it is half phenylalanine.

I imagine reading everything I’ve just written it can feel like that pretty much rules out all the food and drinks in the world! However, there are some raw foods that can be eaten, they just need to be weighed. We weigh them because they don’t contain a high protein content like animal-based products, but they do contain enough protein that means they need to be measured. Vegetables such as potatoes, sweetcorn, bean shoots and peas to name but a few. We count the amount of Phe contained in our food via exchanges, so 80g of boiled potato = 1 exchange. As said before we all have different tolerances, I am allowed 5 exchanges a day however I’ve met people who have been on 25 exchanges and others who have only been on 3.

Branded supermarket foods are a bit easier as they do give you the nutritional information so they will show one packet of crisps is 1.5g of protein (so that will be 1.5 exchanges) however unfortunately the packaging can also not be helpful, as often they will just have how much protein is in food per 100g. The calculation to remember is 100 ÷ the amount of protein the packet says it’s in 100g = 1 exchange.

For example, if Cheerio’s are 9.4g per 100g, 100 ÷ 9.4 = 10.6g, so we would say 11g of Cheerio’s is 1 exchange of protein. There are a few types of food that are completely free of protein, nearly all fruit is, most ‘salad’ vegetables, cucumber, lettuce, tomatoes etc. are and our prescription food, which will be a range of carbohydrate-based foods, such as pasta, rice, bread, biscuits etc.

If you want more details on exchanges, weights of food and what food are free, I really recommend looking on the NSPKU website. The NSPKU is a charity that support families of and people with PKU and they have all sorts of different information on there, from the basics of what foods need to be weighed to all the kinds of milk alternatives, to what sweets are free of protein! Of course, if you have any doubts or questions then do ask the person too, with a lifetime of living with this diet we know a lot about it and if it helps them, there is no such thing as a silly question!


Now that’s the really complicated parts out of the way, it’s time for the more social side of PKU. The hardest thing about PKU isn’t necessarily the counting, the weighing and limiting that we have to do ourselves with our diet, it can also be the social aspect of eating and people cooking for us. Knowing this, it can seem very daunting to cater for someone with PKU when you also just want them to enjoy the experience of eating together and they know the last thing you want to do is to give them something that we can’t have.

If you do want to go out to a restaurant the great thing is, most restaurants now do vegan friendly meals that can be adapted to the PKU diet. Some people try and be helpful by making the person with PKU pick what suits them the best but this isn’t always ideal as if you’re going with a large group, this choice can put a lot of the pressure on them. To help someone with PKU regarding this, the best thing you can do is to first research a few different restaurants in the area using what you already know about PKU and then ask the person with PKU which restaurant they would prefer to go to.

If you want to cook for them or provide food, the best thing you can do is just to sit down and talk to them, to ask what they enjoy, what their own protein tolerances are and what works for them. If you are catering for them, help them feel more comfortable by you being the first one to ask if they would like to bring any food with them, whether it’s their prescription food or their favourite vegan cheese product. If you are not sure on a food product you are giving them, again, be the first to ask whether they would like to check the product. It can feel awkward for us to ask to do both things, as we don’t want to be rude to someone who is trying to cater for us and we don’t want you to think that we don’t trust you but PKU can be very complicated and if we are already given that space to do this before we have to ask about it ourselves, it can be a huge relief.

I have an amazing friend who buys cake for our monthly book club as part of running it, following our conversations about PKU she knows now to look for snacks for me that are under 0.5g of protein each, are in the free-from range or will buy me fresh fruit which she knows I can eat freely. It’s a really lovely thing to do, it helps me feel more included and gives me one less thing to worry about as I know at my book club there is always something I can enjoy. Your effort to include us, cook for us and provide food for us really does make a huge difference in tackling the really hard parts of the PKU diet, so thank you, good luck and again, never be scared to ask!

Important notes to remember

  • Nearly ALL high protein products are off limits
  • ALWAYS check labels in drinks for aspartame
  • 100 ÷ the amount of protein the packet says it’s in 100g = 1 exchange.
  • Every person with PKU has different tolerances and that makes a big difference on what can and can’t be eaten
  • Ask them first what food they would like to bring/if they would like to check it, rather than waiting for them to ask
  • Whenever there is any doubt – just ask, there is no such thing as a silly question!

*Phenylketonuria – NHS (

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