Food allergies

Causes

Food allergies are caused by a reaction of the body’s immune system against food proteins. There are several types of allergic reactions, depending on the immune players involved (e.g. IgE, IgG, T-cells, mast cells, immune complexes, etc), and they give rise to different clinical manifestations. The IgE-mediated, rapidly occurring reactions are the commonly described food allergies. However, other less well understood and often more delayed reactions also exist. These are often collectively referred to as non-IgE-mediated allergies. Genetic and acquired immune disorders, increased passage of allergens through the gut wall (increased intestinal permeability) or the skin are possible reasons for the development of allergies. There is a close interaction between the immune and nervous systems in the intestinal wall and in the skin, explaining the important multidirectional link between immune, pain and psychological reactions. The exact sequences of food protein structure responsible for allergies are increasingly known, allowing prediction of allergic cross-reactions between foods and pollen, for example. At least 30% of individuals with plant allergies have accompanying intestinal allergic responses (See Associations between food and other allergies, cross-reactions). Exercise, stress, alcohol and certain painkillers can induce allergic reactions to foods in predisposed individuals. Reduced vitamin D, zinc and other micronutrients appear to favor the development of allergies.

Frequency in population and natural history

• Adults: 1-4% (based on currently accepted test techniques)
• Children: 5-8% (based on currently accepted test techniques)
• Geographic differences: the most frequent allergies differ according to eating habits.

Most food allergies present in early childhood, but adults can develop new food allergies, especially allergies to fruit and vegetables. The natural history varies with the individual food allergy, however many allergies eventually fade away in later childhood, e.g. by school age. The food allergies most likely to resolve include egg, milk, soy and wheat. Food allergies that typically persist include fish, peanut, shellfish and tree nuts. Overall, the frequency of food and other allergies is increasing.

Individual types of allergy

Allergies to almost any food can occur and have been reported. The most common allergies - constituting approximately 90% of all allergies (often termed ‘IgE-mediated’ or ‘true’ allergies) in the developed Western world are listed below.

• Milk
• Peanut
• Egg
• Soy
• Wheat
• Tree Nut
• Fish
• Seafood
• Vegetables (e.g. carrot, celery, tomato, bean, mustard)
• Meat (e.g. beef, pork)

Latex-food / fruit allergy syndrome: This is the association of latex contact allergy with food allergy, which occurs in 30-80% of cases with latex allergy. Cross-reacting foods are:

• Bananas, avocado, chestnut, apple, kiwi, potato, tomato, melon, papaya. Less common: fig, pineapple, peach, pear, passion fruit, walnut, hazelnut, almond, grapefruit, strawberry, spinach, lettuce, celery, divers spices.

Celiac’s disease: gliadin / gluten allergy occurring in approximately 1% of Northern Europeans and somewhat less in other races. (See Celiac’s disease)

Eosinophilic esophagitis and enteritis: infiltration of esophageal and intestinal lining with allergic cells, resulting in dysfunction. (See Eosinophilic gastrointestinal syndromes). Often associated with food allergies.

Pollen-associated food allergies: Gastrointestinal symptoms occur in at least 30% of individuals with non-food allergies. The commonest of these is the contact allergy known as oral allergy syndrome or food contact hypersensitivity syndrome. Approximately 80% of birch-pollen, and lesser ragweed and mugwort allergic individuals develop immediate itching and swelling in the mouth after ingestion of cross-reacting foods, commonly fruits, nuts and vegetables. (See Associations between food and other allergies, cross-reactions)

Pseudoallergic reactions are defined as clinical reactions resembling allergic reactions but without identifiable immunological sensitization. These include reactions to both natural and artificial food ingredients, as well as drugs and x-ray contrast media. (See Other food reactions)

Symptoms

Allergic reactions involving the alimentary tract can result in a wide range of symptoms, stretching from harmless tingling in the mouth to life-threatening shock reactions, and from lasting a few hours to many days.

At least 30% of sufferers will have symptoms resembling functional bowel disorders, such as irritable bowel syndrome, functional diarrhea or functional dyspepsia: nausea, vomiting, bloating, abdominal cramps and pain, diarrhea, swallowing problems or reflux. Tingling, swelling, itching of the mouth, tongue and throat are frequent allergic signs relating to the oral allergy syndrome (see Associations between food and other allergies, cross-reactions), which is the commonest food allergy in teenagers and adults. Other possible manifestations of food allergies are the common skin reactions, such as itching (urticaria), rash, edema or swelling, and respiratory problems, such as runny nose, sinusitis, asthma or bronchitis. Nervous system reactions, such as tiredness, chronic fatigue, loss of ability to concentrate, migraine headaches and psychiatric disturbances, and musculoskeletal symptoms, including joint and muscle pain, are increasingly recognized. At the extreme end of the spectrum anaphylactic shock can ensue. These reactions are most common in adolescents with co-existing asthma and with peanut allergies.

In infants food protein-induced inflammation of the colon (proctitis, colitis or enteropathy) can be a serious disease, related predominantly to cow’s milk and soy allergy. Characteristic symptoms and signs are protracted diarrhea, vomiting, bloody stools, pain, and malabsorption.

Management

The most important aspect of allergy management is accurate recognition of the offending food(s) or other agent(s) (See Food allergies: tests), as well as cross-reacting allergies (See Associations between food and other allergies, cross-reactions). Permanent exclusion of even small amounts of the recognized component(s) from the diet is still the cornerstone of allergy management for prevention of occurrence and escalation of symptoms. New data show ingestion of small amounts of allergen in egg or milk allergy may in the long term diminish allergic reactions. An elimination diet is often difficult, depending on the food component(s), frequently requiring expert dietary advice and a great deal of personal motivation and discipline. Careful reading of food, drug and in some cases household and cosmetic product labels is advised. Advice on food substitution from an experienced dietician is crucial in the case of fruit or vegetable allergies to prevent deficiencies.

If symptoms persist there is some evidence certain types of anti-allergic medication may be helpful. These include cromoglycate, ketotifen, a combination of antihistamines and probiotics. There is currently insufficient evidence to support the use of steroids or more novel agents, except in the case of eosinophilic intestinal disease. Allergic reactions to food may be very severe, even life-threatening. Medical diagnosis and management advice are important. Emergency treatment injectors (e.g. Epipen™) should be carried in case of severe allergic reactions. Immunotherapy for some allergies, especially the pollen-associated food allergies, may be successful in a subset of individuals, however even then the effect is often not long-term. Other treatments in development include vaccination, anti IgE and other antibodies, toleragen peptides, recombinant epitopes for hyposensitization, anti-mast cell drugs, as well as molecular modification of the offending food protein.

The Recommendations for Prevention of Allergy by the American Academy of Pediatrics have recently been revised and now conclude: Current evidence does not support a major role for maternal dietary restrictions during pregnancy or lactation in the reduction of allergies. There is evidence that breastfeeding for at least 4 months, compared with feeding formula made with intact cow milk protein, prevents or delays the occurrence of atopic dermatitis, cow milk allergy, and wheezing in early childhood. At present, there are insufficient data to document a protective effect of any dietary intervention beyond 4 to 6 months of age for the development of atopic disease.

Information nuggets

• Heating of food by microwave (e.g. 90˚C or 190˚F) or cooking will eliminate or reduce allergic reactions to many foods, but not peanuts.
• In oral allergy syndrome peeling of the fruit or eating freshly picked or unripe fruit may reduce allergic reactions.
• In highly allergic individuals inhalation of the food allergen may be sufficient for even strong allergic reactions. Examples are flour, egg white or crustaceans.
• Immunotherapy (‘allergy shots’) of hay fever may reduce the intensity of associated food allergies.
• Seek medical treatment if a severe food allergy requiring use of the emergency injector occurs, as usually a second, delayed reaction can occur 4 to 12 hours after the first reaction.
• Intestinal malabsorption (e.g. lactose or fructose) and slow clearing of intestinal content may predispose to food allergy.
• Food allergies and food intolerances (See Food intolerances) may co-exist. If conscientious exclusion of one type of food does not result in major symptom relief, consider having other intolerances or allergies excluded.
• Skin prick and blood IgE tests correlate incompletely with intestinal allergic reactions. These results therefore never exclude food allergies. They can, however, provide some useful guidance.
• Breastfeeding for at least 6 months and the early consumption of probiotics during and immediately after pregnancy may reduce food-induced allergic reactions in children.
• Although currently not accepted by most allergy specialists, food IgG4 blood tests have been shown to result in significant and useful symptom improvements in patients with functional bowel disorders, when identified foods were excluded from the diet.
• Food additive allergies are rare, but may be severe (e.g tartrazine, monosodium glutamate, “natural food additives”). This can be suspected if symptoms occur after food or beverage some, but not all of the time, suggesting the reaction only occurs in the presence of the additive.
• Food allergies and anaphylaxis may be provoked by exercise, which do not occur otherwise. This is especially common with wheat allergy.

Links to literature

• Sicherer SH, Sampson HA. Food allergy. J Allergy Clin Immunol 2010;125(Suppl 2): 116-125 (click to download pdf).
• Cochrane S et al. Factors influencing the incidence and prevalence of food allergy. Allergy 2009;64:1246-1255 (click to download pdf).
• Bischoff S. Food allergies. Current Treatment Options Gastroenterology. 2007;10:34-41 (click to download pdf).
• Nowak-Wegrzyn A, Sampson HA. Adverse reactions to foods. Med Clin N Am 2006;90:97-127 (click to download pdf).
• Chapman JA, Bernstein IL, Lee RE, Oppenheimer J, Nicklas RA, Portnoy JM, Sicherer S, Schuller DE, Spector SL, Khan D, Lang D, Simon RA, Tilles SA, Blessing-Moore J, Wallace D, Teuber SS. Food allergy: a practice parameter. Ann All Asthma Immunol 2006;96:S1-S68 (click to download pdf).
• Bischoff S, Crowe SA. Gastrointestinal food allergy: new insights into pathophysiology and clinical perspectives. Gastroenterology 2005;128:1089-1113 (click to download pdf).
• http://www.foodallergens.info