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Adverse Food Reactions

March 13, 2015

punk-rock-veggies-scott-youngAdverse food reactions
By Dr Adrian Morris

Food allergy is a complex area of medicine. Up to 20 per cent of the population have adverse reactions to food and claim to be food allergic. But on testing, around one per cent of adults and four per cent of children are found to be truly food allergic.

Food allergy

What are the causes? In children, common allergy provoking foods include cows milk protein, hens egg white, wheat, soya bean, codfish and peanuts. In adults, nuts (including brazilnuts, almond, hazelnut, peanut and walnut), fruits (such as peach, apple, strawberry and citrus fruit), and vegetables (such as celery, tomato, onion, garlic and parsley) are common allergens. Seafood such as fish, mussels, crab, prawn, shrimp and squid may also cause allergic reactions.

What are the symptoms? Typically, an immediate type of food allergic reaction involves the immune system. Traces of the offending food rapidly lead to symptoms of generalised rash, itching, body swelling, breathing difficulties and even collapse. Peanut anaphylaxis is a good example where traces of the food are absorbed in the mouth or intestine. This leads to the rapid release of histamine from cells and allergic tissue swelling.

Some people with the oral allergy syndrome get a localised red itchy mouth and throat on eating certain fruit, vegetables and nuts. Delayed reactions to food are becoming more common and this may be the basis of eczema in infants. Coeliac disease occurs due to a delayed immune reaction to gluten in wheat. This causes intestinal membrane damage with resultant diarrhoea, abdominal bloating and anaemia resulting in malnutrition.

Food intolerance

What are the causes? Food Intolerance – for example lactose intolerance – may be caused by the lack of a specific digestive enzyme. This is a remarkably common condition. Natural histamine may be too rapidly absorbed from food in the diet and effectively lead to a histamine ‘rush’ that mimics an allergy.

Then there are adverse reactions to chemical preservatives and additives in food such as seen with sulphites, benzoates, salicylates, monosodium glutamate, caffeine, aspartame and tartrazine.

What are the symptoms? These adverse food reactions are of slower onset, do not involve the immune system and are not usually life threatening. Reactions are usually dose related. With small amounts of the food being tolerated but larger amounts leading to reactions such rashes, flushing, abdominal pain, vomiting, diarrhoea and palpitations. These are by far the most common adverse food reaction seen in general practice.

The lack of a specific enzyme in the body may lead to the build up of toxic by-products and histamine, which then mimic the symptoms of an allergy. This is called a ‘pseudo-allergic’ reaction.

Food toxicity and aversion

Poisons may naturally occur in foods such as mushrooms and potatoes. Bacteria in putrefying fish can cause toxic food poisoning called ‘schromboid toxicity’. These reactions occur in all people who consume the toxin and do not involve a digestive intolerance or an immune reaction.

Some people convince themselves – with no sound basis – that they are ‘food allergic’ and will vomit if given the particular food. If the food is concealed or hidden then they consume it with no ill effect. Their reaction is strictly on a psychological basis, and it is often difficult to convince these people that they are not allergic.

Diagnosing food allergy

Food allergy can be diagnosed by means of skin-prick tests to various foods or by RAST testing. Skin testing with fresh food extracts is more accurate. The gold standard in food allergy is the Double Blind Placebo Controlled Food Challenge (DBPCFC) test under careful supervision in a hospital.

If no food can be identified, but an allergic reaction is strongly suspected, a two- to four-week elimination diet is performed. The person lives on a limited number of foods, which are unlikely to cause allergies, such as lamb, rice, pears and sweet potato. Then once the allergic symptoms settle, foods are slowly reintroduced one at a time to identify the offending food. This should only be done under the supervision of a dietician as a child can end up in a state of malnutrition on a prolonged few-food diet.

Food Intolerance is very difficult to diagnose as there are no reliable blood or skin tests available. The suspected food has to be eliminated from the diet and a clinical improvement documented. The offending food should then be reintroduced again for a short period to confirm the adverse reaction and hence the intolerance.

Food allergy prevention

For high-risk families (those families with severely allergic parents or siblings) it is recommended that the pregnant mother avoid cigarette smoking and highly allergenic foods in the last half of pregnancy. She should try to exclusively breastfeed the child and continue the avoidance of allergenic foods. If the mother is unable to breastfeed then a hypoallergenic formula-milk should be considered.

Delay the introduction of solid foods until six months of age and then restrict first foods to lamb meat, chicken, rice, sweet potatoes, carrots and pears. Avoid cow’s milk, eggs, wheat, fish, soya, citrus for the first year and introduce nuts and peanuts only in the third year. Food labels need to be carefully read to take account of contents in tinned and processed food. Try wherever possible to avoid foods containing additives and preservatives.

Once food allergy has been confirmed, the most effective preventative treatment is complete avoidance of that food. If the food cannot be completely avoided, oral sodium chromoglycate may help to prevent adverse reactions.


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