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Food Labels

Reading food labels

When you have a child with PKU it is particularly important and useful to know how to read food labels. This will allow you to check the protein content of foods and work out if the food is suitable for your child’s diet.

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This might seem confusing and overwhelming at first, but with practice this will become easier.

The protein in food is counted in grams of protein. 1g of protein equals 50mg of phe in most foods.

1g of protein = 50mg of phe

When feeding your child commercially available, packaged food, it is important to know how to interpret the food label.

This enables you to -

1) Decide if the food needs to be counted

2) Decide how much can be included in your child’s diet if it is to be counted.

It is also important to compare the
declared serving size of the packaged food to the amount that your child would eat. This will allow you to consider the amount of protein your child would eat from that food, which helps to plan

Protein values for foods without a
nutrition information table ie. fresh fruit and vegetables, can be obtained from your dietitian or the PKU Handbook (ASIEM).

Always check labels for the added sweetener ASPARTAME (E951 or E962) which is not permitted as it is a source of phenylalanine.

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

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

Nutritional Information

Serving Size: 33g (2 bsicuits)

Per Sevre Per 100g
Energy (kcal) 118 355
Protein (g) 4.1 12.4
Fat, Toal (g) 0.4 1.3
Carbohydrate (g) 22.1 67

This label provides information on the energy content shown as 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 4.1g of protein. 

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How to read food labels

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.

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Reviewing the nutrition information panel enables you to decide if a food contains significant amounts of protein and so needs to be counted in your child’s diet.

If the protein is 0.5g or less per 100g, then this food is classed as protein 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 your child will eat, and therefore how many grams of protein they consume. Your dietitian will instruct on the number of grams of protein allowed each day, and how they are to be spread throughout the day.

The ASIEM PKU Handbook provides a comprehensive list of products which are protein free. For further information, speak to your dietitian.

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Calculating Protein in Foods

Knowing a food’s protein content per 100g,  enables you to calculate how much of that food provides ONE gram of protein.

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For example, this yoghurt contains:

Calculating Phe Label

5.1g of protein per 100g. So, 100 ÷ 5.1 = 20g

Therefore, 20g is equal to 1 gram of protein.


A nutrition information panel will also state the amount of protein per serve/portion.

The table below shows how many grams of protein are in ONE portion of food.

If ONE portion of food contains 0.3g protein or less, then the amount of protein ONE portion provides, is considered protein- free.  However, if your child eats more than ONE portion, this amount of food will contain greater than 0.3g protein, and so it will be counted towards the daily protein allowance.

Protein Content (g/per portion) Grams of Protein
0 - 0.3 Free (1 portion only)
0.4 - 0.7 0.5
0.8 - 1.2 1
1.3 - 1.7 1.5
1.8 - 2.2 2


If you do not have the protein content per portion available, then you can still work out the amount of protein per portion of food that your child eats using the protein content for 100g.

See 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 grams of protein per portion of food.

If a child eats 20g of yoghurt:

5.1 (protein per 100g) x 20 (amount eaten)

÷ 100 = 1 gram of protein


Once your child is old enough, encourage them to read food labels and calculate their intake of protein at meals and snacks. Until then, at mealtimes it will be useful to get them familiar with knowing which foods contain protein and which ones are protein-free.

Understanding food labels will encourage independence and help to prevent your child always relying on you to do the work! Plenty of practice will increase their ability and confidence.

Always refer to the food label, ASIEM PKU Handbook and your dietitian for the most up-to-date nutritional information.

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