Allergic reactions to food may manifest in the form of nausea, vomiting, flatulence, abdominal pain, cramping, diarrhoea and with non gastrointestinal illnesses such as rashes, eczema, swelling, nasal allergy, wheeze, angioedema and in some cases, even life threatening anaphylaxis.

Fresh fruit, vegetables and spices may cause local tissue reactions on the lips, in the mouth and in the throat - this is the so-called Oral Allergy Syndrome (OAS). Oral allergy tends to occur more commonly in individuals who are allergic to Birch and Grass pollen. Some food allergic people may also develop flushing, shortness of breath, hives and fainting following strenuous exercise. This condition is known as food related Exercise-induced Anaphylaxis. It can occur for up to 12 hours after ingesting offending food such as shellfish, celery and wheat. Evidence now suggests that Coeliac Disease may be due to delayed T cell-mediated allergy to dietary gliadin found in wheat, rye barley and oats. Preservatives and other additives tend to predominantly induce reactions outside the intestine such as rashes, wheezing and exacerbate eczema. There is still considerable controversy as to whether the hyper-activity syndrome and migraine are allergic in nature - so far scientific evidence is in conflict, but so-called Myalgic Encephalomyelitis (M.E.) and the Chronic Systemic Candidiasis syndrome do not appear to have any food allergy basis.

Only when the adverse reaction occurs immediately after eating the causative food may the diagnosis of food allergy be easy to make. Otherwise with delayed reactions to food, such as when cell mediated and immune complex mediated mechanisms are involved, the offending food is very difficult to isolate.

Infants tend more commonly to develop allergies to Hen egg white, Cows milk protein, Wheat, Peanuts, Bony Fish, Citrus and even Soya protein, whilst adults tend to be allergic to foods such as Bony Fish, Shellfish, Peanuts, Tree-nuts, Tomatoes and Chocolate. Although these foods are more commonly implicated in food allergy, almost any food can be a potential allergen.

Food allergy usually manifests in babies with feeding problems and a strong family background of allergy. The high-risk infant is the one who has one or both parents with allergic disease. Those with a single affected parent have about a 37% risk of developing some form of allergy while those with both parents affected have about a 62% risk. The diagnosis is dependent on a clinical history suggestive of food allergy, with symptom improvement on withdrawing the offending food from the diet. The physical examination is often not particularly informative. There are a number of Diagnostic tests, which determine IgE mediated allergy by means of skin or blood testing. Skin Scratch Test solutions are commercially available from ALK Abello and Diagenics for most foods, but fresh extracts are preferable and should be used to test for fruit allergy. Pharmacia Diagnostics market a number of food allergy screening tests such as Total IgE and the CAP RAST fx5 Paediatric Food Mix which tests for 6 common paediatric food allergens (Milk, Egg, Wheat, Peanut, Soya and Peanut). In adults the CAP RAST fx1, fx2 and fx3 are additional screening tests for nuts, seafood and cereals respectively. There are also up to 160 individual CAP RAST tests available for different foods.

Neither skin prick tests nor CAP RASTs alone can absolutely exclude or confirm the possibility of a food allergy. For example, Prof. Bahna (USA) has shown that in Cow’s Milk allergy confirmed by double-blind challenge testing, both skin testing and RAST showed similar although suboptimal degrees of reliablity. The sensitivity (true positive test) was 44% for skin testing and 56% for RAST, and the specificity (true negative test) was 67% for both. Therefore provocation challenge testing is the best way of confirming a suspected food allergy.

The diagnostic "gold standard" in food allergy is the double blind placebo controlled food challenge test (DBPCFC). In reality it is very difficult to perform this challenge outside the orderly environment of an academic inpatient hospital. In the Primary Care setting, if a specific food is implicated, a trial exclusion diet is implemented, followed by the diagnostic re-introduction of the offending food.

Nutramigen, Pregestimil or Alfare

Comminuted chicken

Nutramigen, Pregestimil or Alfare

Rice cereal and rice cakes

Lamb or chicken meat

Cooked pears or bananas

Herb or Rooibos Tea (only sugar may be added)

Rice cereals, "Rice Krispies" and rice bread

Lamb and chicken meat

Cooked or canned pears, apricots, prunes or their juices

Sunflower or olive oil, non-dairy margarine

Cooked beetroot, sweet-potato, carrots, parsnips

Lettuce

If no obvious food is suspected, then a simple elimination diet for two to four weeks is suggested. It should consist of either a extensively hydrolysed infant formula or only hypo-allergenic foods such as: lamb meat or chicken, polished rice, rice cakes, pears, bananas, water and sunflower or olive oil. In children, if despite the elimination diet, the symptoms persist, an elemental diet such as Neocate, a hypoallergenic amino acid based formula, should be considered. If Neocate is unavailable then Comminuted chicken or lamb meat may be used as a "homemade" hypoallergenic formula. The elimination diet for children is very limited and obviously not well adhered to by adults. In adults a greater number of foods may rather be used in a "few food" elimination diet.

The "few food" diet for adults - if offending food is not apparent

The following foods are considered to have a low potential for causing allergies

Meat: Lamb, chicken

Vegetables: Rice, sweet-potato, carrots, rhubarb, asparagus, Fruit: Pears, banana, apricots, apple, pineapple (All peeled)

Fat: Non-dairy margarine, sunflower and olive oil

Other: Herb or Rooibos tea, water, honey, sugar, sago

Supplement: Calcium 400 - 800mg/day and added vitamin B

Once the allergy has settled after 4 weeks on the elimination diet, other foods are slowly re-introduced one at a time at weekly intervals. Each new food may be tried in small test quantities and then given in normal amounts every day for a week until the allergy provoking food is identified. Most foods can then slowly be re-introduced during the provocation testing period. Adults are tested by slowly re-introducing fish and shellfish, pork and beef, nuts, chocolate, legumes, white potatoes, tomatoes, oranges, strawberries, cows milk, wheat, eggs, pizza, fresh fruit and finally hens eggs. Provocation testing should not be performed if there is a history of anaphylaxis to a particular food (such as peanuts).

Food allergy prevention measures should only be considered in babies with one or both parents manifesting definite allergic disease. Maternal diet in early pregnancy seems to play little or no role in the infant becoming food allergic, so dietary manipulation is not recommended at this stage. However, in the last 3 months of pregnancy and during breastfeeding, cigarette smoking should be strongly discouraged and milk, egg and peanuts avoided. The most effective form of food allergy prevention in the "at risk" infant is unsupplemented breast-feeding for at least the first four to six months of age. Breast-feeding should be encouraged as it reduces exposure to foreign proteins, helps to mature the gut barrier early, has anti-inflammatory properties and reduces the risk of infections, which can act as allergy triggers. The breastfeeding mother must be careful to avoid eating common allergenic foods such as eggs, cow’s milk and peanuts, as traces can pass into the breast milk and sensitize the infant.

If exclusive breast-feeding cannot be established or maintained then a partially hydrolysed infant milk formula or an extensively hydrolysed formula such as Nutramigen, Pregestimil or Alfare should be used. These hydrolysed formulae are produced by heat or enzymatic hydrolysis of cows milk casein or whey, rendering them hypoallergenic. The more complete the hydrolysis process the less allergenic the milk. But extensively hydrolysed formulas are very expensive and tend to have an unpleasant taste, which is poorly tolerated by older infants. Soya milk formulas now seem to have "fallen from favour" in food allergy prevention as soya is a potential allergen. Goats milk can cross react with cows milk (both contain B-Lactglobulin), so is also a poor alternative and lacks adequate folic acid. Apparently Donkey’s milk is closest in composition to human’s milk!

Food allergy is most prevalent in the paediatric age group. Eggs and cows milk seem to be the commonest causes of food allergy followed by peanut and wheat. Often infants will also develop an allergy to their soya milk and may even have an adverse reaction to "hypoallergenic" formulas. Once the food allergy is diagnosed, an exclusion diet is instituted. Calcium (400-800mg/day) needs to be supplemented in cows milk-free diets, and Vitamin B in wheat free diets. A certain amount of cross-reactivity occurs between foods of similar classes and this should be borne in mind if symptoms recur on specific food avoidance. For example if allergic to peanuts, then there is a high risk of being allergic to beans, peas, lentils, carob, senna and liquorice (all members of the legume family). This may be due to the presence of a pan-allergen called Profilin common to fruit, grass and vegetables and which accounts for the cross-reactivity we see between different food It would appear that allergic reactions to fruit and vegetables, which often coexist with pollen allergy, are on the increase. Birch pollen allergic people can have cross-reactions to apples and other fruit, grass pollen allergic people may react to cereals and tomatoes, while those allergic to latex, react to avocado, chestnut, banana and kiwi-fruit. Hidden allergen sources also need to be identified as processed foods are notoriously inadequately labeled.

If an essential foodstuff needs to be excluded from the diet, a dietitian should be consulted for advice so as to ensure the diet is nutritionally adequate. Restrictive diets run the risk of inducing malnutrition, are costly to implement, cause anxiety in the family, result in the child being over protected and socially isolated. If the diet does not work, then great disappointment and anger may ensue, affecting the whole family.

The main thrust in food allergy treatment is specific allergen avoidance. Medical treatment may sometimes need to be instituted if symptoms are severe and includes; antihistamine, adrenaline and corticosteroid medication. All people with documented food anaphylaxis should wear a Medic Alert bracelet and carry an adrenaline injection (Epipen) for self-administration. Allergy prevention medication such as cetirizine (Zirtek) should be recommended in the paediatric age group. This may reduce food allergen reactivity and slow the so-called "Allergy March" onto Eczema, Asthma and Nasal Allergy which are common sequels to food allergy. At present studies are being undertaken in Europe to assess how effective preventer-medicines are in stopping the "allergic march"- this is the so-called Early Treatment of the Allergic Child (ETAC) concept. The role of oral desensitization vaccines need to be further evaluated, but they may be a future therapeutic option for severe reactions to unavoidable food allergens.

Finally, cautious re-introduction of a "prohibited" food can be attempted after 6-12 months as the natural history of food allergy is for gradual improvement. Foods implicated with anaphylaxis should not be re-introduced outside a controlled hospital environment.

Most clinical food allergic reactions are immediate and IgE mediated. A non-IgE or T-cell mediated allergic reaction might be considered when an allergic basis is still suspected despite conventional skin prick and CAP RAST tests being negative.

When evaluating food allergy one must also be wary of unproven diagnostic and therapeutic regimes. Chiropractors have popularized "food allergy" using dubious diagnostic tests such as Applied Kinesiology and Vega testing - these tests are of no value and are not reproducible. Practitioners should be aware of the fact that the publicity and "popularity" surrounding food allergy has spawned a new form of "Munchausen by proxy" - where the parent, convinced that their child’s symptoms are secondary to food allergy, institutes bizarre and nutritionally deficient diets.

All exclusion diets must include adequate amounts of protein, carbohydrate, essential fats, vitamins and minerals otherwise malnutrition will occur. The advice of a qualified dietician should be sought if foods are excluded from the diet for any length of time.