Food allergy is defined as an adverse immunological response to a food protein.
[1]
Sicherer SH, Sampson HA. 9. Food allergy. J Allergy Clin Immunol. 2006 Feb;117(2 Suppl Mini-Primer):S470-5.
http://www.ncbi.nlm.nih.gov/pubmed/16455349?tool=bestpractice.com
Although approximately 20% of people alter their diet due to a perceived adverse reaction to food, only 6% of young children and 3.7% of adults in the US have a true food allergy.
[1]
Sicherer SH, Sampson HA. 9. Food allergy. J Allergy Clin Immunol. 2006 Feb;117(2 Suppl Mini-Primer):S470-5.
http://www.ncbi.nlm.nih.gov/pubmed/16455349?tool=bestpractice.com
People who believe they have a food allergy may suffer from a metabolic intolerance to a particular food; for example, lactose intolerance. Others may be sensitive to a particular pharmacologically active component of food, such as caffeine or tyramine. Some people may mistake bacterial food poisoning as a reaction to a particular food.
[1]
Sicherer SH, Sampson HA. 9. Food allergy. J Allergy Clin Immunol. 2006 Feb;117(2 Suppl Mini-Primer):S470-5.
http://www.ncbi.nlm.nih.gov/pubmed/16455349?tool=bestpractice.com
[2]
Ebisawa M, Ito K, Fujisawa T; Committee for Japanese Pediatric Guideline for Food Allergy, The Japanese Society of Pediatric Allergy and Clinical Immunology, The Japanese Society of Allergology. Japanese guidelines for food allergy 2017. Allergol Int. 2017 Apr;66(2):248-64.
http://www.allergologyinternational.com/article/S1323-8930(17)30005-9/fulltext
http://www.ncbi.nlm.nih.gov/pubmed/28285847?tool=bestpractice.com
Although all of these scenarios involve food, they do not result from an abnormal immune response to a particular food protein and therefore cannot be considered a true food allergy.
[3]
Zopf Y, Baenkler HW, Silbermann A, et al. The differential diagnosis of food intolerance. Dtsch Arztebl Int. 2009 May;106(21):359-69.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2695393/
http://www.ncbi.nlm.nih.gov/pubmed/19547751?tool=bestpractice.com
Rather, some of them, such as lactose intolerance and sucrase-isomaltase deficiency, are considered non-immune food intolerances, and others such as tyramine and sulphite reactions are considered non-immune food sensitivities.
Pathophysiology
Food allergies can be classified into disorders that are IgE-mediated, cell-mediated, or a combination of the two.
[4]
Sicherer SH. Food allergy. Lancet. 2002 Aug 31;360(9334):701-10.
http://www.ncbi.nlm.nih.gov/pubmed/12241890?tool=bestpractice.com
IgE-mediated food allergies result from abnormal sensitisation to a food allergen that results in specific IgE production. However, a positive skin prick test or IgE test on its own does not indicate that a patient has a food allergy; it only means that they are sensitised to a food. Only the history, or an oral food challenge, can identify true food allergens. Once produced, food-specific IgE binds on to mast cells. When the particular food is subsequently ingested, the food is broken down and absorbed. The food antigen then binds to the IgE on the mast cells, leading to mast-cell degranulation and release of mediators that cause the signs and symptoms of the allergic reaction.
[4]
Sicherer SH. Food allergy. Lancet. 2002 Aug 31;360(9334):701-10.
http://www.ncbi.nlm.nih.gov/pubmed/12241890?tool=bestpractice.com
IgE-mediated food disorders include anaphylaxis and oral allergy syndrome.
Cell-mediated reactions involve T cells, and may occur several hours to days after ingesting the offending food.
[4]
Sicherer SH. Food allergy. Lancet. 2002 Aug 31;360(9334):701-10.
http://www.ncbi.nlm.nih.gov/pubmed/12241890?tool=bestpractice.com
Food protein-induced enterocolitis, enteropathy, proctocolitis, and coeliac disease are examples of cell-mediated food-allergic diseases.
Mixed IgE- and cell-mediated food diseases include atopic dermatitis and the eosinophilic gastroenteropathies, such as eosinophilic oesophagitis.
[4]
Sicherer SH. Food allergy. Lancet. 2002 Aug 31;360(9334):701-10.
http://www.ncbi.nlm.nih.gov/pubmed/12241890?tool=bestpractice.com
Non-immune food intolerances often result from deficiencies in the enzyme that breaks down the food component into absorbable substrates in the small intestine.
[5]
Heyman MB; Committee on Nutrition. Lactose intolerance in infants, children, and adolescents. Pediatrics. 2006 Sep;118(3):1279-86.
http://pediatrics.aappublications.org/content/118/3/1279.full
http://www.ncbi.nlm.nih.gov/pubmed/16951027?tool=bestpractice.com
Non-immune food sensitivities to biogenic amines (such as tyramine) or to food additives (such as monosodium glutamate) are more controversial and are debated vigorously in the literature.
[6]
Jansen SC, van Dusseldorp M, Bottema KC, et al. Intolerance to dietary biogenic amines: a review. Ann Allergy Asthma Immunol. 2003 Sep;91(3):233-40.
http://www.ncbi.nlm.nih.gov/pubmed/14533654?tool=bestpractice.com
[7]
Geha RS, Beiser A, Ren C, et al. Multicenter, double-blind, placebo-controlled, multiple-challenge evaluation of reported reactions to monosodium glutamate. J Allergy Clin Immunol. 2000 Nov;106(5):973-80.
http://www.ncbi.nlm.nih.gov/pubmed/11080723?tool=bestpractice.com
However, sensitivities to sulphites found in foods such as red wine and dried fruit have been confirmed as a trigger of bronchospasm in sulphite-sensitive asthmatic patients.
[8]
Simon RA. Update on sulfite sensitivity. Allergy. 1998;53(46 Suppl):78-9.
http://www.ncbi.nlm.nih.gov/pubmed/9826006?tool=bestpractice.com
