How Much Should My Child Eat?

Children with PKU should eat roughly the same amounts as a child of the same age without PKU. Throughout their childhood, many things will change in your child’s life including their appetite. 

Even in children of the same age, there can be a big difference in their food intake; 

• Smaller children will generally need less food than taller children. 
• Less active children will generally need less food than more active children. 

If the amount your child eat reduces significantly, or you are worried about your child’s weight, contact their dietitian for advice. 

When a child has PKU, their diet will have extra considerations, for example some foods; 

• will need to be avoided entirely such as meat and fish. 
• can only be eaten in measured quantities (phe exchanges), these include bread and cereal. 
• must be swapped for specially manufactured low protein alternatives, such as milk and pasta. 

Your child’s specialist metabolic team will continue to see your child regularly. You can use these appointments as an opportunity to ask any questions you might have about your child’s individual diet. 

The following information outlines the 5 main food groups your child should include in their low protein diet:

• Fruit and vegetables
• Starchy carbohydrates
• Protein (Phe exchanges and protein substitutes)
• Dairy and dairy free alternatives
• Oils and spreads

Eatwell guide: https://www.nhs.uk/live-well/eat-well/the-eatwell-guide/

The following sections provide information on the main food groups your child should eat. We have provided average amounts as a guide only. As always, please consult your child’s dietitian for information specific to your child.

The National Society for Phenylketonuria (NSPKU) has developed a booklet containing a list of permitted fruits and vegetables that you can refer to. This can be downloaded from their website or you can contact them to request a copy. Fruit and vegetables can be included as part of a meal or offered as a snack option. Children should aim for at least 5 permitted, age appropriate portions of fruit and vegetables every day.

Allow your child to eat larger portions of permitted fruits and vegetables if they wish, as these are low energy, high nutrient foods.

Fruits and vegetables can be fresh, frozen, tinned or dried. A typical portion size would fit into the palm of your child’s hand, for example:

As most carbohydrate-based foods contain protein your child will mostly rely on specially manufactured low protein foods, such as low protein bread, pasta, cereal and rice. There are a wide variety of these specially manufactured low protein foods available, speak to your child’s dietitian for further information on these.

Specially manufactured low protein carbohydrate-based foods provide energy, variety and bulk to the diet. They should be offered at each meal and can also be offered as a snack. Here are some example portion sizes:

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Many of the specially manufactured low-protein carbohydrate-based foods (e.g. low protein breads and pastas) are low in fibre although higher fibre versions are available. It is important to include other sources of fibre such as permitted fruits and vegetables in your child’s diet. 

Meat, fish and eggs contribute to a child without PKU’s protein intake, however the phe in these foods is much too high for a child with PKU. Protein is needed for growth and your child will get most of the protein they require from their protein substitute. It is very important that they take all their protein substitute daily as advised by their dietitian.

A small amount of protein will also come from their daily phe exchanges, for example, from certain vegetables and starchy carbohydrates. These phe exchanges must be measured with scales.

The amount of protein substitute your child needs and the number of phe exchanges allowed each day will be advised by your child’s dietitian.

Dairy and dairy free alternatives provide energy, nutrients and variety to your child’s diet. There are many low protein dairy alternatives available. You should speak to your dietitian about the most suitable options and amounts for your child.

Example portion sizes:

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Unlike regular dairy foods, low-protein dairy alternatives may contain minimal amounts of vitamins and minerals, such as calcium. However, these nutrients will also be provided by your child’s protein substitute.

Fats are a rich source of energy, and very important in childhood where recommended amounts are higher than they are in adulthood. Fats are also a source of Omega 3 & 6 fatty acids which are important for health. Fats can be used to provide extra energy if your child is struggling to gain or maintain their weight. You should speak to your dietitian about the most suitable options and amounts for your child.

Choose healthier unsaturated varieties such as vegetable oil or olive oil-based/low fat spread.

Here are some example portion sizes:

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Fluid is essential for good health. It is important that children drink frequently throughout the day. Offer a drink with each meal and snack. Water or permitted drinks should be taken after your child’s protein substitute.

Daily fluid recommendations:

1 medium size glass ≈ 200 ml

1 mug ≈ 250 ml

1 cup ≈ 200 ml

≈ = approximate measurements

Tips:

• Water or permitted drinks should be taken after your protein substitute.
• Extra fluids may be required in very hot weather or if your child is particularly active.
• The best drink between meals and snacks is water.
• Drinks containing permitted sweeteners should be well diluted.
• Always check labels for added sweetener such as Aspartame (E951 or E962), which contain Phe and is therefore not suitable for those with PKU.

These foods are high in sugar and fat and include protein-free and/or low protein puddings, cakes, biscuits and sugary drinks. Although they provide extra energy to the diet, they contain few other nutrients. Permitted sweets, low protein chocolate alternatives and low protein biscuits can be offered to children occasionally. 

It is important to be careful and aware of how much of these foods and sugary drinks your child is having. High sugar intakes can lead to tooth decay and unnecessary weight gain. They may also reduce your child’s appetite for their meals which contain important food groups.

It is common for some children at certain stages in childhood, to be constantly hungry! This is more likely to be the case if they are going through a growth spurt or being particularly active through school and extra-curricular activities such as swimming, running, football, etc. This can be challenging for any parent and more so if your child is on a restricted diet. This can be managed by increasing the amount of permitted foods eaten. Discuss the best options to manage this increased appetite with your dietitian. It may be the case that your child needs to obtain higher amounts of the specially manufactured low-protein foods and will need a change in their prescription.

The information provided here should be used as a guide only and every child, whether they have PKU or not will have a different appetite. The best advice you will receive on the types of food and the amount your child should be eating will come from your dietitian.