How Much Should a Teenager Eat?

A suggested healthy routine is to eat 3 meals and 2-3 nutritious snacks a day to optimise your energy and get all of the nutrition you need to stay fit and healthy.  

The ‘Eatwell Guide’ provides a visual image of the different types of foods and drinks that people without PKU should eat to ensure a balanced diet. The guide we have provided in this section has been adapted for a low protein diet.  

The following information outlines the 5 main food groups you should consume in your low protein diet and on average how much you should eat in a day: 

•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 you should eat. We have provided average amounts as a guide only, to help give you an idea of quantities. As always, please consult your dietitian for information specific to you.  

The National Society for Phenylketonuria (NSPKU) has developed a booklet containing a long 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 hard copy. Fruit and vegetables can be included as part of a meal or eaten as a snack option. You should aim for at least 5 portions of permitted fruit and vegetables every day. 

Although most fruits and vegetables are exchange free. some will need to be counted as exchanges. Please refer to NSPKU Dietary Booklet or your dietitian for more information.

You can eat larger portions of permitted fruits and vegetables if you wish, as these are low energy foods and full of nutrition. 

Fruits and vegetables can be fresh, frozen, tinned or dried. Examples of typical portion sizes are given below: 

Figures are intended as a guide only.  

As most carbohydrate-based foods contain protein you will mostly rely on specially manufactured low protein foods, such as low protein bread, pasta, cereal and rice. There is a wide variety of these low protein foods available - speak to your dietitian if you are interested in trying something new. 

Some regular starchy carbohydrate foods may be used as exchanges. Please refer to the NSPKU Dietary Booklet or your dietitian for more information

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

Figures are intended as a guide only. 

Many of the specially manufactured low-protein carbohydrate-based foods such as low protein breads and pastas are low in fibre although in some products higher fibre versions are now available. Fibre is important as it keeps the food moving through your body. It is therefore important that you think about including other sources of fibre in your diet (e.g. permitted fruits and vegetables) on a daily basis. 

Meat, fish and eggs contribute to the protein intake of an individual without PKU but, as you may know, the phe in these foods is too high for you. Protein is needed for growth and building muscles. You will get most of the protein you need from your protein substitute. It is very important that you take all your recommended protein substitute every day to ensure you grow to your full potential and maintain your muscle mass throughout your teenage years. If you are thinking about a change of protein substitute, speak to your dietitian – there may be new protein substitutes available that you have not tried yet.   

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

The amount of protein substitute you need and the number of phe exchanges allowed each day will be advised by your metabolic team. 

Some regular dairy foods may be used as exchanges. Please refer to the NSPKU dietary booklet or your dietitian for information.

Dairy and dairy free alternatives provide energy, nutrients and variety to your diet. There are many low protein dairy alternatives available such as plant and coconut-based milks and cheeses. You should speak to your dietitian about the most suitable options and amounts for you. Not all of these products are fortified with calcium so check the labels to see which ones are best. 

Example portion sizes: 

Figures are intended as a guide only. 

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 protein substitute. 

Fats and oils often get a bad name, but you do need fat in your diet. Fats are a rich source of energy which you need every day, to supply your body with essential fatty acids and enable you to absorb the fat-soluble vitamins A, D, E and K from the food that you eat. There are different types of fats, some more beneficial than others. It is best to choose unsaturated varieties such as vegetable oil or olive oil-based/low fat spread.   

Some fats in particular are necessary in your diet, especially for growth and the growing brain as well as your skin. Your body cannot make some omega-3 and -6 fatty acids so you must get them from your diet.

You may want to take an omega-3 supplement if your protein substitute doesn’t already contain this. Your metabolic team will be able to tell you what’s appropriate for you. 

Here are some example portions sizes: 

Figures are intended as a guide only. 

Fluids are essential for good health. Your body is mostly water and water has so many functions – for example, removing waste products and transporting nutrients around your body. It is important that you drink frequently throughout the day.  Make sure you have a drink with each meal and snack.  

Daily water recommendations: 

1 medium size glass = 200ml

1 mug = 250ml

1 cup = 200ml

== approximate measures

Tips: 

• Water or permitted drinks should be taken after your protein substitute. 

• Extra fluids may be required in very hot weather or if you are particularly active. 

• The best drink between meals and snacks is plain or sparkling water. It’s protein and sugar free. 

• 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 you. 

These foods are high in sugar and fat and include your prescription foods too e.g. protein free/low protein puddings, cakes, biscuits and sugary drinks. Although they provide extra energy to the diet, they are low in other necessary nutrients. Permitted sweets like low protein chocolate alternatives and low protein biscuits should not be part of the diet too often and are usually best eaten occasionally. 

High sugar intakes can lead to tooth decay and unnecessary weight gain. They may also reduce your appetite for more nutritious foods that benefit your health. 

You may sometimes go through phases when you always seem to be hungry! This is more likely to be the case if you are going through a growth spurt or being particularly active. As your diet is already restricted, this can be challenging. 

So, what should you eat? You can increase the amount of permitted foods. Discuss your best options to manage your increased appetite with your dietitian. It may also be the case that you need to obtain higher amounts of the specially manufactured low-protein foods. In this case, you will need to change your prescription.  

The information provided here should be used as a guide only - everyone is different. The best advice you will receive will come from your dietitian.