Healthy eating with PKU
The diet for Phenylketonuria (PKU) can be very hard to follow. Avoiding high protein foods on a daily basis whilst eating out, socialising and working can pose for difficulties. When adding healthy eating and weight loss into daily routine, things can become even more difficult. However, like the general population it is really important to aim for a healthy Body Mass Index to avoid developing any associated conditions such as diabetes and heart disease.
See below for the guidelines regarding BMI:
| BMI | Classification |
| <18.5kg/m2 | Underweight |
| 18.5-25kg/m2 | Healthy weight |
| 26-30kg/m2 | Overweight |
| >30kg/m2 | Obese |
How to work out your BMI:
= Weight (kg) / Height (m) x Height (m)
Firstly, let’s review some of the common myths that we regularly hear from people with PKU and set the record straight. (NB: If you are following the pre-conception diet or pregnant, please speak to your dietitian before making any changes to your diet):
I can’t lose weight if I have PKU; my phenylalanine levels will increase
To an extent this is partly true. If you go on a crash diet and deprive your body of calories you will become catabolic. This means your body will break down its own muscle stores for energy and in doing so release phenylalanine into your blood, increasing your levels. However, if you sensibly cut your calories down and aim to lose 1-2lbs a week steadily, this should not be a problem.
I need to eat regularly and snack to keep my phenylalanine levels within range
This links in with myth one and was true when you were younger. When you are growing your body needs lots of calories and you will have probably been advised to eat lots of low protein foods and snack regularly. This keeps your energy intake up for growing and activities and stops you becoming catabolic, causing higher phenylalanine levels. As you age, calorie needs reduce and therefore you can cut down on the amount you eat. You may still want to snack but fruit is always a better option.
My protein substitute “my medicine” is really high in calories and causes me to gain weight
Firstly you should not refer to your protein substitute as medicine. The PKU diet means you cannot eat foods high in protein and therefore as the name suggests your protein substitute is your protein substitute. In fact, if you look at the table below and the calorie content of common protein substitute versus some high protein foods they are similar or much less. You need to think as your protein substitute being the meat, fish, eggs, beans or lentils you are not having with a meal instead of an extra.
| Protein Substitute | Calories | High protein food | Calories |
| 1 x Cooler 20 | 124 | Chicken breast (120g) ovenbaked | 166 |
| 1 x PKU Air 20 | 97 | ½ a tin of baked beans | 185 |
| 1 x Express 20 (unflavoured) | 99 | 1 x Salmon fillet (120g) ovenbaked | 269 |
| 1 x PKU Lophlex Powder (unflavoured) | 91 | Lean Minced beef (120g) panfried | 176 |
| 1 x PKU Lophlex Sensation | 166 | Lentils (50g) | 164 |
| 1 x Lophlex LQ Juicy 20 | 116 | 2 large eggs | 156 |
| 25 x Phlexy 10 tablets | 95 | Pork Chop (120g) | 244 |
I can’t have sugar-free drinks because they have aspartame in them. So I choose fruit juices, smoothies and normal fizzy drinks and squashes instead.
This is partly true. A lot of common diet drinks do have aspartame in them which contains phenylalanine. However, many supermarkets such as Asda and Sainsburys now have their own diet drink range and use sweeteners such as sorbitol and sucralose. These are fine to have in PKU and can help cut your calorie and sugar intake down. There has been a lot of media interest in fruit juices and smoothies and their many health claims. Some claims are true; they are a good source of Vitamin C and they are one of your 5 a day if consumed in the recommended portion. However, because many pieces of juiced or blended fruit fit into one bottle of juice or smoothie they are very concentrated in sugar and calories. They should not be a drink consumed everyday as have similar or much higher sugar content to full-sugar fizzy drinks. See below:
| Drink (full-sugar) (100mls) | Sugar (g) | Calories | Drink
(100ml) |
Sugar (g) | Calories |
| Coca Cola | 10.6 | 42 | Innocent Smoothie | 10.5 | 54 |
| Sprite | 6.6 | 27 | Fresh Orange Juice | 9.0 | 44 |
| Fanta | 6.6 | 29 | Pomegranate Juice | 11.7 | 48 |
All my exchanges are unhealthy. I find it hard not to have chips, crisps and biscuits.
It is hard to find quick and easy foods on the go sometimes for exchanges and a quick packet of crisps or a biscuit can be quick and easy. These are not the healthiest choices and not the best for your waistline. Some healthy exchanges that you could use instead include vegetables such as peas and sweetcorn, potato, breakfast cereals, plain popcorn, crackers, measured amounts of normal rice, small amounts of cream cheese (if you have a higher phe tolerance 35g is 3 exchanges). Cream crackers are an exchange each and small fromage frais (45g) are 2.5 exchanges. Something different and tasty.
As you can see there are many myths associated with the PKU diet and maintaining a healthy weight and BMI. The diet is very tricky and takes dedication and motivation but it is possible to lose weight healthily and keep your blood phenylalanine levels in range.
Thank you for your post, as it helps me to learn on what to do on the PKU diet n be successful at weight loss n maintaining blood phe levels at the same time. I find this very challenging n I wasnt raised this way n have be eet n totally lost. I find your article very helpful. However, I also disagree on the protein substitute n using that in place of my meat portion. I cannot do that, as I starve.
Thank you for your kind comment, I am glad it has helped you. We will take note of your last comment, thanks.
This article does not reflect my experience at all. I suggest you try living on 6g protein, working, being a mother, having PKU and losing weight at the same time. I found it patronising. I have a BM index of 34.
Thanks for your comment, sorry you found it patronising. The article was aimed at giving a general overview for people with PKU as often healthy eating info for the general public is not always suitable.
Enjoyed the article but disagree on considering your “formula” your meat in each meal…
mainly because formula is so much less filling than meat as a PKU patient who has on occasion eaten meat.
It would be nice to have a list of diet drinks PKU patients can drink… I have had this fear instilled in me since I was 7 that if I drink a diet drink I will burst in to flames, and it would be nice to have verified ones I could drink with no concern.
Thanks for your comment Marco. Yes many people know not to have diet drinks with aspartame in for PKU. Check the ingredients lists, it is only the sweetener aspartame that contains phenylalanine, the other sweeteners don’t and would be ok to have.
Your article is very well written and interesting.
Thanks Nicola – very kind 🙂 x
I absolutely love this article! I have PKU and am a personal trainer with several clients that have PKU. All of them have come to me for fat loss. I always tell them that in terms of diet they need to speak to their clinic because my sports nutrition qualifications don’t cover me to work with anyone with medical conditions, but that they MUST take all of their PKU supplements. They are always sceptical!
Thanks Kate! You send very sensible. The supplements are so important as you well know 🙂 x