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


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.