What Is a Phenylketonuria Diet?

For those with phenylketonuria, a low-phenylalanine diet can help avoid intellectual impairment and other consequences. High protein foods are avoided and low protein foods are the main emphasis of the diet.

A genetic mutation that results in low amounts or no phenylalanine hydroxylase (PAH) enzyme is known as phenylketonuria (PKU). Phenylalanine (Phe), an amino acid, is typically broken down by PAH.

PKU patients experience PHE buildup in their bodies. If PKU treatment is not initiated soon after birth, infants with PKU may develop intellectual impairment because Phe is toxic to brain cells.

PKU is mostly treated with a particular diet. The goal here is to cut back on Phe consumption without sacrificing overall nutrition quality. To find out more about the PKU diet, continue reading.

What is the goal of a phenylketonuria diet?

You follow the PKU diet specifically, and you do so for the rest of your life. The PKU diet aims to achieve these:
  • Restricting natural intake of Phe: Phe is present in protein sources since amino acids are the building blocks of proteins. People with PKU therefore need to have a low-protein diet.
  • Using a protein substitute: People with PKU still need to receive other amino acids from their food, even if the PKU diet tries to restrict Phe consumption. Usually, this is accomplished by applying a protein replacement mix.
  • Maintaining a good nutrition status: It's critical that PKU sufferers eat a balanced diet. You might need to take supplements of vitamins and minerals or mix them into the protein substitute recipe, to be sure of this.
The general goal of PKU care is to maintain blood Phe levels between 120 to 360 micromoles per litre (umol/L).

Your doctor will periodically check the amount of Phe in your blood if you have PKU. This entails taking a tiny sample of your finger's blood and putting it on a designated card. After that, the card is transported to a lab for analysis.

Together, you and a dietitian will create a PKU diet plan that suits your requirements. They might periodically modify this strategy. For instance, during growth spurts, your blood Phe levels and nutritional requirements may alter.

The importance of following a phenylketonuria diet

A low-phenylalanine diet has been shown to lower phenylalanine levels and shield individuals with PKU from cerebral impairment and other neurological problems.

When you stop the PKU diet, Phe in your body can begin to accumulate once more. This may result in a range of neurological alterations, including
  • intellectual disability
  • problems with focus, memory, or problem-solving
  • difficulties coordinating vision and movement
  • difficulty at school or work
  • behavioral or mood changes
  • tremors
  • fatigue 

What foods can a person with phenylketonuria eat?

Foods that are permissible for consumption by those with PKU include:
  • most veggies and fruits
  • sugars found in jams, syrups, and honey
  • fats like vegetable oil, butter, and margarine
  • low-protein starches such as arrowroot, tapioca, and cornflour
  • beverages including fruit juice, coffee, and green or black tea
  • herbs and spices
An important amino acid is phenomenal. Essential amino acids are not produced by your body naturally; instead, you must get them through food. You cannot entirely cut off Phe from your diet as a result.

People with PKU can consume carefully controlled amounts of specific foods, such as cereals or potatoes, to obtain some dietary Phe.

In addition, your doctor may prescribe low-protein alternatives for some foods that are especially designed for individuals with PKU. Among the instances are:
  • flour mixes
  • breads
  • egg and milk substitutes
  • pastas
  • pizza bases

How to calculate the amount of phenylalanine in a food
Your food plan will contain a daily Phe allowance if you have PKU. You are allowed to consume this much Phe in a single day. Every PKU patient has a different daily Phe allowance.

The Phe content of food can be determined in several ways, and there isn't much data to support the superiority of any particular approach. This online brochure offers practical calculations for Phe content and protein swaps.

Additionally, your physician can issue you a card for exchanging proteins and suggest apps that will allow you to monitor your intake of vitamin Phe.

What foods should a person with phenylketonuria avoid?

Protein-rich foods should be avoided by those with PKU because they contain Phe. Among them are:
  • meat and poultry
  • fish
  • eggs
  • beans
  • lentils
  • milk and cheese
  • nuts and seeds
  • grains like:
  1. wheat
  2. barley
  3. quinoa
  4. oats
  5. rye
  • gelatins
  • soy products

Furthermore, aspartame should be avoided by those who have PKU. This is because aspartame gets changed by the body into Phe.


A low-phe diet is the major management strategy for PKU. Maintaining low blood Phe levels and avoiding PKU sequelae including intellectual disability and other neurological problems can be achieved by adhering to the PKU diet.

This calls for eating a low-protein diet because Phe is contained in protein. While avoiding foods like meats, eggs, and dairy, people with PKU can eat most fruits and vegetables, sweets, fats, and low-protein carbohydrates.

You should discuss all dietary plans with your physician.

Even though Phe is an essential amino acid, getting enough of it in your diet is still crucial if you have PKU. Each person with PKU is unique and has a daily allotment of Phe. You can learn from your doctor how to monitor how much Phe you take in each day.

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