Define food allergy and food intolerance. what is the difference between allergies and intolerance

Food hypersensitivity is used to refer broadly to both food intolerances and food allergies.[1] There are a variety of earlier terms which are no longer in use such as «pseudo-allergy».[2]

Food intolerance reactions can include pharmacologic, metabolic, and gastro-intestinal responses to foods or food compounds. Food intolerance does not include either psychological responses[3] or foodborne illness.

A non-allergic food hypersensitivity is an abnormal physiological response. It can be hard to determine the poorly tolerated substance as reactions can be delayed, dose-dependent, and a specific reaction-causing compound may be found in numerous foods.[4]

  1. Metabolic food reactions are due to inborn or acquired errors of metabolism of nutrients, such as in lactase deficiency, phenylketonuria and favism.
  2. Toxins may either be present naturally in food, be released by bacteria, or be due to contamination of food products.[5] Toxic food reactions are caused by the direct action of a food or substance without immune involvement.[5]
  3. Pharmacological reactions are generally due to low-molecular-weight chemicals which happen either as natural compounds, such as salicylates and amines, or to food additives, such as preservatives, colouring, emulsifiers and taste enhancers.

    These chemicals are capable of causing drug-like (biochemical) side effects in susceptible individuals.[5]

  4. Gastro-intestinal reactions can be due to malabsorption or other GI Tract abnormalities.
  5. Immunological responses are mediated by non-IgE immunoglobulins, where the immune system recognises a specific food as a foreign body.
  6. Psychological reactions involve manifestation of clinical symptoms caused not by food but by emotions associated with food. These symptoms do not happen when the food is given in an unrecognisable form.[5]

Elimination diets are useful to help in the diagnosis of food intolerance.

There are specific diagnostic tests for certain food intolerances.[5][6][7]


Reactions to chemical components of the diet may be more common than true food allergies,[citation needed] although there is no evidence to support this. They are caused by various organic chemicals occurring naturally in a wide variety of foods, animal and vegetable, more often than to food additives, preservatives, colourings and flavourings, such as sulfites or dyes.[13] Both natural and artificial ingredients may cause adverse reactions in sensitive people if consumed in sufficient amounts, the degree of sensitivity varying between individuals.

Pharmacological responses to naturally occurring compounds in food, or chemical intolerance, can happen in individuals from both allergic and non-allergic family backgrounds.

Define food allergy and food intolerance. what is the difference between allergies and intolerance

Symptoms may start at any age, and may develop quickly or slowly. Triggers may range from a viral infection or illness to environmental chemical exposure.

Define food allergy and food intolerance. what is the difference between allergies and intolerance

Chemical intolerance occurs more commonly in women, which may be because of hormone differences, as numerous food chemicals mimic hormones.[citation needed]

A deficiency in digestive enzymes can also cause some types of food intolerances. Lactose intolerance is a result of the body not producing sufficient lactase to digest the lactose in milk;[25][26] dairy foods which are lower in lactose, such as cheese, are less likely to trigger a reaction in this case.

Define food allergy and food intolerance. what is the difference between allergies and intolerance

Another carbohydrate intolerance caused by enzyme deficiency is hereditary fructose intolerance.

Celiac disease, an autoimmune disorder caused by an immune response to the protein gluten, results in gluten intolerance and can lead to temporary lactose intolerance.[27][28]

The most widely distributed naturally occurring food chemical capable of provoking reactions is salicylate,[18] although tartrazine and benzoic acid are well recognised in susceptible individuals.[29][30][31] Benzoates and salicylates happen naturally in numerous foods, including fruits, juices, vegetables, spices, herbs, nuts, tea, wines, and coffee.

Define food allergy and food intolerance. what is the difference between allergies and intolerance

Salicylate sensitivity causes reactions to not only aspirin and NSAIDs but also foods in which salicylates naturally happen, such as cherries.

Other natural chemicals which commonly cause reactions and cross reactivity include amines, nitrates, sulphites and some antioxidants. Chemicals involved in aroma and flavour are often suspect.[20][32][33][34]

The classification or avoidance of foods based on botanical families bears no relationship to their chemical content and is not relevant in the management of food intolerance.[citation needed]

Salicylate-containing foods include apples, citrus fruits, strawberries, tomatoes, and wine, while reactions to chocolate, cheese, bananas, avocado, tomato or wine point to amines as the likely food chemical.

Thus, exclusion of single foods does not necessarily identify the chemical responsible as several chemicals can be present in a food, the patient may be sensitive to multiple food chemicals and reaction more likely to happen when foods containing the triggering substance are eaten in a combined quantity that exceeds the patient’s sensitivity thresholds. People with food sensitivities own diverse sensitivity thresholds, and so more sensitive people will react to much smaller amounts of the substance.[5][9][20][33][34][35][36][37][38][39]


There is emerging evidence from studies of cord bloods that both sensitization and the acquisition of tolerance can start in pregnancy, however the window of main harm for sensitization to foods extends prenatally, remaining most critical during early infancy when the immune system and intestinal tract are still maturing.[citation needed] There is no conclusive evidence to support the restriction of dairy intake in the maternal diet during pregnancy in order to prevent.

This is generally not recommended since the drawbacks in terms of loss of nutrition can out-weigh the benefits. However, further randomised, controlled trials are required to examine if dietary exclusion by lactating mothers can truly minimize risk to a significant degree and if any reduction in risk is out-weighed by deleterious impacts on maternal nutrition.[51]

A Cochrane review has concluded feeding with a soy formula cannot be recommended for prevention of allergy or food intolerance in infants.

Further research may be warranted to determine the role of soy formulas for prevention of allergy or food intolerance in infants unable to be breast fed with a strong family history of allergy or cow’s milk protein intolerance.[52] In the case of allergy and celiac disease others recommend a dietary regimen is effective in the prevention of allergic diseases in high-risk infants, particularly in early infancy regarding food allergy and eczema. The most effective dietary regimen is exclusively breastfeeding for at least 4–6 months or, in absence of breast milk, formulas with documented reduced allergenicity for at least the first 4 months, combined with avoidance of solid food and cow’s milk for the first 4 months.[53][54]


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Food intolerance are every other adverse reactions to food. Subgroups include enzymatic (e.g. lactose intolerance due to lactase deficiency), pharmacological (e.g. reactions against biogenic amines, histamine intolerance), and undefined food intolerance (e.g. against some food additives).[40]

Food intolerances can be caused by enzymatic defects in the digestive system, can also result from pharmacological effects of vasoactive amines present in foods (e.g.

histamine),[6] among other metabolic, pharmacological and digestive abnormalities.

Allergies and intolerances to a food group may coexist with separate pathologies; for example, cow’s milk allergy (CMA) and lactose intolerance are two distinct pathologies.

Define food allergy and food intolerance. what is the difference between allergies and intolerance


Diagnosis of food intolerance can include hydrogen breath testing for lactose intolerance and fructose malabsorption, professionally supervised elimination diets, and ELISA testing for IgG-mediated immune responses to specific foods. It is significant to be capable to distinguish between food allergy, food intolerance, and autoimmune disease in the management of these disorders.[41] Non-IgE-mediated intolerance is more chronic, less acute, less obvious in its clinical presentation, and often more hard to diagnose than allergy, as skin tests and standard immunological studies are not helpful.[8] Elimination diets must remove every poorly tolerated foods, or every foods containing offending compounds.

Clinical investigation is generally undertaken only for more serious cases, as for minor complaints which do not significantly limit the person’s lifestyle the cure may be more inconvenient than the problem.[5]

IgG4 tests are invalid; IgG4 presence indicates that the person has been repeatedly exposed to food proteins recognized as foreign by the immune system which is a normal physiological response of the immune system after exposure to food components.[42][1] Although elimination of foods based on IgG-4 testing in IBS patients resulted in an improvement in symptoms,[43] the positive effects of food elimination were more likely due to wheat and milk elimination than IgG-4 test-determined factors.[44] The IgG-4 test specificity is questionable as healthy individuals with no symptoms of food intolerance also test positive for IgG-4 to several foods.[45]

Diagnosis is made using medical history and cutaneous and serological tests to exclude other causes, but to obtain final confirmation a Double Blind Controlled Food Challenge must be performed.[6] Treatment can involve long-term avoidance,[46] or if possible re-establishing a level of tolerance.

Define food allergy and food intolerance. what is the difference between allergies and intolerance

Today there are numerous methods available such as Cytotoxic testing, MRT testing, Elisa Testing, Microarray Elisa Testing, and ELISA/ACT. Allergy US reviewed these methods and Microarray technology appears to be the most dependable among them.[47][48][49][50]

Signs and symptoms

Food intolerance is more chronic, less acute, less obvious in its presentation, and often more hard to diagnose than a food allergy.[8] Symptoms of food intolerance vary greatly, and can be mistaken for the symptoms of a food allergy. While true allergies are associated with fast-acting immunoglobulin IgE responses, it can be hard to determine the offending food causing a food intolerance because the response generally takes put over a prolonged period of time.

Thus, the causative agent and the response are separated in time, and may not be obviously related.

Define food allergy and food intolerance. what is the difference between allergies and intolerance

Food intolerance symptoms generally start about half an hour after eating or drinking the food in question, but sometimes symptoms may be delayed by up to 48 hours.[9]

Food intolerance can present with symptoms affecting the skin, respiratory tract, gastrointestinal tract (GIT) either individually or in combination. On the skin may include skin rashes, urticaria (hives),[10]angioedema,[11] dermatitis,[12] and eczema.[13] Respiratory tract symptoms can include nasal congestion, sinusitis, pharyngeal irritations, asthma and an unproductive cough.

GIT symptoms include mouth ulcers, abdominal cramp, nausea, gas, intermittent diarrhea, constipation, irritable bowel syndrome (IBS),[6][7][9] and may include anaphylaxis.[13]

Food intolerance has been found associated with irritable bowel syndrome and inflammatory bowel disease,[14] chronic constipation,[15] chronic hepatitis C infection,[16] eczema,[17] NSAID intolerance,[18] respiratory complaints,[19] including asthma,[20]rhinitis and headache,[21][22]functional dyspepsia,[23]eosinophilic esophagitis[9] and ENT illnesses.[21][24]