Phenylketonuria (PKU) is a rare inherited condition in which there is a build up of the amino acid phenylalanine in the body. PKU is tested for at birth of newborns by measuring phenylalanine levels in the heel-prick blood test. All babies should have this test as it allows treatment to start early in life. High levels of phenylalanine are toxic to the brain, and will affect brain development, and the PKU sufferer will develop learning and behavioural difficulties.
However, PKU is a treatable condition. Phenylalanine is found in the protein part of the food we eat and the treatment is a low protein diet. This means that high protein foods such as meat, cheese, poultry, eggs and milk are not permitted. Instead the diet is supplemented with specially formulated protein sources which contain no phenylalanine. This diet is very effective at lowering levels of phenylalanine and allows normal growth and development of the child.
Basic principles of the diet:
Treatment consists of a diet containing only the amount of phenylalanine which is essential for growth and development.
- Meat, fish, cheese, eggs and nuts are rich in protein and therefore phenylalanine so they are not allowed.
- Other foods which contain some protein such as potato, milk and cereals are given in small measured quantities so that the blood phenylalanine, which is measured regularly, is kept within safe limits. These measured foods are spread out between the day's meals. The quantities allowed will vary from person to person.
- Most fruit, some vegetables and salads can be taken in normal quantities but avoid excess use. Sugar, jam, syrups, and fats such as butter, lard and cooking oil can be used freely. There are many manufactured foods which are low in protein and are available on prescription for the person with PKU, including low protein bread, biscuits, flour, spaghetti and other pasta which can all be taken freely and can be used to provide variety in the diet.
- As high protein foods cannot be eaten these have to be replaced by a special protein mixture from which the phenylalanine has been removed. These protein substitutes are all available on prescription and will provide the essential 'safe' protein for growth and development. It is crucial that these are taken regularly with meals and evenly spread out over the day.
- Vitamins and minerals should also be supplemented into the diet. Some protein substitutes include these, but if they are not then vitamin and mineral supplements are available on prescription.
- Specially formulated low protein wheat based products are available, including bread, flour, biscuits and pasta. Some of these are available on prescription, others can be purchased through your pharmacy or at specialist stores.
Traffic Light System
To make things easier for a PKU diet, a traffic light system is advocated:
- Red - STOP! Do not eat these foods.
- Amber - Go Cautiously! These foods can be eaten in controlled amounts.
- Green - Go! These foods may be eaten in normal quantities.
Red List - Stop! Foods Not Allowed - High in Phenylalanine
- Meat - all kinds of read meat, poultry and offal
- Fish - all kinds including oily, white and shellfish and fish products
- Cheese all kinds including cheese spreads.
- Nuts & seeds
- Wheat products – ordinary bread, flour, cakes, biscuits, pasta.
- Soya - and soya products, e.g. TVP.
- Aspartame - an artificial sweetener found in some fizzy drinks, squashes, cordials, puddings and chewing gums, aswell as some tablet and granulated sweeteners. Aspartame contains phenylalanine and therefore it must be avoided. Foods and drinks containing aspartame will be labelled either Artificial Sweetener: Aspartame or Artificial Sweetener: E951. They will also be labelled 'Contains a source of phenylalanine'. Aspartame is also used in some drugs. Please check with your doctor or pharmacist before taking any drugs.
Amber List - Go Cautiously! Foods containing some Phenylalanine to be taken with Caution.
Basic list of 50mg exchanges of food - these items should be measured accurately (weigh food after cooking unless otherwise stated).
Single Cream 40ml
Double Cream 60ml
Soured Cream 35ml
Boiled and mashed 80g
Chips - frozen, fresh, oven, 45g
Canned, new (drained weight) 100g
Instant mashed potato 10g
Baked Beans 20g
Bamboo shoots, raw 60g
Broccoli tops, fresh, boiled 30g
Brussels sprouts, boiled 35g
Mange tout peas, raw 30g
Peas - fresh, frozen & petit poise 25g
Spinach, boiled 25g
Spring greens 35g
Sweetcorn kernels & baby corn, canned drained 35g
Corn on the cob, raw 55g (4cm)
Sweet potato, boiled 60g
Avocado, flesh only 55g
Passion fruit 35g
Rice Krispies 15g
Sugar Puffs 15g
Weetabix, Weetaflakes 10g
Shredded Wheat 10g
Ready Brek 10g
Puffed Wheat 5g
Bran Flakes 10g
Oatmeal (raw) & rolled oats 10g
Rice (raw) white or brown 15g
Rice (boiled) white or brown 45g
Green list - Go! Foods containing small quantities of phenylalanine which can be used in normal quantities. Take care to avoid excess.
Most types (fresh, tinned, raw or cooked in sugar) including apples, apricots fresh and dried, bilberries, blackberries, cherries, clementines, cranberries, currants (black, red and dried), damsons, figs (fresh, not dried), fruit pie filling, fruit salad, gooseberries, grapes, grapefruit, greengages, guavas, lemons, limes, loganberries, lychees, kiwi fruit, kumquats, mandarins, mangoes, melon, water melon, medlars, mulberries, nectarines, olives, oranges, paw paw, peaches (not dried), pears, pineapple, plums, pomegranate, prunes, quince, raisins, raspberries, rhubarb, satsumas, strawberries, sultanas, tangerines, mixed peel, angelica, glace cherries, ginger.
Artichoke, aubergine, French beans, beetroot, cabbage, capers, carrots, cauliflower, celeriac, celery, chicory, courgettes, cucumber, endive, gherkin, okra, leek, lettuce, marrow, mushrooms, cress, onion, pickled onion, parsley and all herbs, parsnip, peppers (red, green, yellow, orange), pumpkin, radish, swede, sweet potato, tomato, turnip, watercress, fennel, kohl. All clear vegetable pickles in vinegar e.g. pickled onions, gherkins, red cabbage.
Cornflour, arrowroot, custard powder (not instant custard), blancmange powder (not blancmange mix or chocolate flavour), sago, tapioca. (Not ready to serve milk puddings).
Butter, margarine (not margarine spreads which contain buttermilk e.g. some low fat spreads), lard, vegetable fats and oils (liquid and solid).
Sugar: white, brown, caster, icing; glucose. Jam, honey, marmalade, syrup, treacle, boiled sweets, rock, candy, sherbet, barley sugar, candy floss.
Food essences and colourings: e.g. vanilla, cochineal, peppermint, almond essence. Salt and pepper, herbs and spices, curry powder, vinegar, mustard.
Baking powder, bicarbonate of soda, cream of tartar.
Special Olay formulated low protein products: low protein bread, flour, biscuits, pasta, etc.
Water, soda water, mineral water, fizzy drinks, e.g. lemonade, coke, fruit cordial and squash, instant tea, black coffee, pure fruit juices.
NB: Always check the labels. Do not consume at all if the list of ingredients includes aspartame.
The following fruits and vegetables if taken in large quantities add a significant amount of phenylalanine to the day's intake. Restrict to one serving of any one item per day. These foods may be used in small quantities such as in vegetable stews, sauces and fruit salad.
Banana - one small per day
Fruit mincemeat (sweet mincemeat)
The following meal plan is an example plan of a healthy diet which is suitable for a child with PKU and includes protein substitute. However it is imperative that you consult your doctor before commencing such a regimen, and blood levels of phenylalanine are monitored regularly. Portion sizes and 50mg exchanges have not been noted, as these will have to be varied according to blood phenylalanine levels, age, activity, growth and development. Use the plan to give you an idea of what are healthy nutritious foods to include for a balanced diet and for structure, but don't forget to vary your food choices and to drink plenty of water through the day.