Food intolerance
Encyclopedia
Food intolerance or non-allergic food hypersensitivity is a term used widely for varied physiological responses associated with a particular food, or compound found in a range of foods.

Food intolerance is negative reaction, often delayed, to a food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...

, beverage, food additive
Food additive
Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...

, or compound found in foods that produces symptoms in one or more body organs and systems, but it is not a true food allergy
Food allergy
A food allergy is an adverse immune response to a food protein. They are distinct from other adverse responses to food, such as food intolerance, pharmacological reactions, and toxin-mediated reactions....

. A true food allergy requires the presence of IgE
IGE
IGE was one of the largest services company buying and selling virtual currencies and accounts for MMORPG. During its peak time, it had offices in Los Angeles, China , and headquarters & customer service centre in Hong Kong. IGE was one of the main monopoly in virtual economy services, also known...

 antibodies against the food, and a food intolerance does not.

Food intolerances can be classified according to their mechanism. Intolerance can result from the absence of specific chemicals or enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s needed to digest
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

 a food substance, as in hereditary fructose intolerance. It may be a result of an abnormality in the body's ability to absorb nutrients, as occurs in fructose malabsorption
Fructose malabsorption
Fructose malabsorption, formerly named "dietary fructose intolerance," is a digestive disorder in which absorption of fructose is impaired by deficient fructose carriers in the small intestine's enterocytes. This results in an increased concentration of fructose in the entire intestine.Fructose...

. Food intolerance reactions can occur to naturally occurring chemicals in foods, as in salicylate sensitivity
Salicylate sensitivity
Salicylate sensitivity, also known as salicylate intolerance, is any adverse effect that occurs when a normal amount of salicylate is introduced into a person's body...

. Drugs sourced from plants, such as aspirin, can also cause these kinds of reactions. Finally, it may be the result of non-IgE-mediated immune responses.

Definitions

Non-allergic food hypersensitivity is the medical name for food intolerance, loosely referred to as food hypersensitivity, or previously as pseudo-allergic reactions. Non-allergic food hypersensitivity should not be confused with true food allergies.

Food intolerance reactions can include pharmacologic, metabolic, and gastro-intestinal responses to foods or food compounds. Food intolerance does not include either psychological responses or foodborne illness
Foodborne illness
Foodborne illness is any illness resulting from the consumption of contaminated food, pathogenic bacteria, viruses, or parasites that contaminate food, as well as chemical or natural toxins such as poisonous mushrooms.-Causes:Foodborne illness usually arises from improper handling, preparation, or...

.

A non-allergic food hypersensitivity is an abnormal physiological response. It can be difficult to determine the poorly tolerated substance as reactions can be delayed, dose-dependant, and a particular reaction-causing compound may be found in many foods.
  • Metabolic food reactions are due to inborn
    Inborn error of metabolism
    Inborn errors of metabolism comprise a large class of genetic diseases involving disorders of metabolism. The majority are due to defects of single genes that code for enzymes that facilitate conversion of various substances into others...

     or acquired errors of metabolism of nutrients, such as in diabetes mellitus
    Diabetes mellitus
    Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...

    , lactase deficiency, phenylketonuria
    Phenylketonuria
    Phenylketonuria is an autosomal recessive metabolic genetic disorder characterized by a mutation in the gene for the hepatic enzyme phenylalanine hydroxylase , rendering it nonfunctional. This enzyme is necessary to metabolize the amino acid phenylalanine to the amino acid tyrosine...

     and favism.
  • Pharmacological reactions are generally due to low-molecular-weight chemicals which occur either as natural compounds, such as salicylates
    Salicylate sensitivity
    Salicylate sensitivity, also known as salicylate intolerance, is any adverse effect that occurs when a normal amount of salicylate is introduced into a person's body...

     and amines, or to food additive
    Food additive
    Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...

    s, such as preservatives, colouring, emulsifiers and taste enhancers. These chemicals are capable of causing drug-like (biochemical) side effects in susceptible individuals.
  • Gastro-intestinal reactions can be due to malabsorption
    Malabsorption
    Malabsorption is a state arising from abnormality in absorption of food nutrients across the gastrointestinal tract.Impairment can be of single or multiple nutrients depending on the abnormality...

     or other GI Tract abnormalities.
  • Immunological responses are mediated by non-IgE immunoglobulins, where the immune system recognises a particular food as a foreign body.
  • Toxins may either be present naturally in food, be released by bacteria, or be due to contamination of food products. Toxic food reactions are caused by the direct action of a food or substance without immune involvement.
  • Psychological reactions involve manifestation of clinical symptoms caused not by food but by emotions associated with food. These symptoms do not occur when the food is given in an unrecognisable form.


Elimination diet
Elimination diet
An elimination diet is a method of identifying foods that an individual cannot consume without adverse effects. Adverse effects may be due to food allergy, food intolerance, other physiological mechanisms , or a combination of these...

s are useful to assist in the diagnosis of food intolerance. There are specific diagnostic tests for certain food intolerances.

Signs and symptoms

Non-IgE-mediated food hypersensitivity (food intolerance) is more chronic, less acute, less obvious in its presentation, and often more difficult to diagnose than a food allergy.
Symptoms of food intolerance vary greatly, and can be mistaken for the symptoms of a food allergy
Food allergy
A food allergy is an adverse immune response to a food protein. They are distinct from other adverse responses to food, such as food intolerance, pharmacological reactions, and toxin-mediated reactions....

. While true allergies are associated with fast-acting immunoglobulin IgE responses, it can be difficult to determine the offending food causing a food intolerance because the response generally takes place over a prolonged period of time. Thus the causative agent and the response are separated in time, and may not be obviously related. Food intolerance symptoms usually begin about half an hour after eating or drinking the food in question, but sometimes symptoms may delayed up to 48 h.

Food intolerance can present with symptoms affecting the skin, respiratory tract
Respiratory tract
In humans the respiratory tract is the part of the anatomy involved with the process of respiration.The respiratory tract is divided into 3 segments:*Upper respiratory tract: nose and nasal passages, paranasal sinuses, and throat or pharynx...

, gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....

 (GIT) either individually or in combination. On the skin may include skin rashes, urticaria
Urticaria
Urticaria is a kind of skin rash notable for pale red, raised, itchy bumps. Hives is frequently caused by allergic reactions; however, there are many non-allergic causes...

 (hives), angioedema
Angioedema
Angioedema or Quincke's edema is the rapid swelling of the dermis, subcutaneous tissue, mucosa and submucosal tissues. It is very similar to urticaria, but urticaria, commonly known as hives, occurs in the upper dermis...

, dermatitis, and eczema
Eczema
Eczema is a form of dermatitis, or inflammation of the epidermis . In England, an estimated 5.7 million or about one in every nine people have been diagnosed with the disease by a clinician at some point in their lives.The term eczema is broadly applied to a range of persistent skin conditions...

. Respiratory tract symptoms can include nasal congestion
Nasal congestion
Nasal congestion is the blockage of the nasal passages usually due to membranes lining the nose becoming swollen from inflamed blood vessels. It is also known as nasal blockage, nasal obstruction, blocked nose, stuffy nose, or stuffed up nose.Nasal congestion has many causes and can range from a...

, sinusitis
Sinusitis
Sinusitis is inflammation of the paranasal sinuses, which may be due to infection, allergy, or autoimmune issues. Most cases are due to a viral infection and resolve over the course of 10 days...

, pharyngeal
Human pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...

 irritations, asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...

 and an unproductive cough
Cough
A cough is a sudden and often repetitively occurring reflex which helps to clear the large breathing passages from secretions, irritants, foreign particles and microbes...

. GIT symptoms include mouth ulcer
Mouth ulcer
A mouth or oral ulcer is an open sore in the mouth, or rarely a break in the mucous membrane or the epithelium on the lips or surrounding the mouth. The types of mouth ulcers are diverse, with a multitude of associated causes including: physical abrasion, acidic fruit, infection, other medical...

s, abdominal cramp, nausea
Nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...

, gas
Flatulence
Flatulence is the expulsion through the rectum of a mixture of gases that are byproducts of the digestion process of mammals and other animals. The medical term for the mixture of gases is flatus, informally known as a fart, or simply gas...

, intermittent diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...

, constipation
Constipation
Constipation refers to bowel movements that are infrequent or hard to pass. Constipation is a common cause of painful defecation...

, irritable bowel syndrome
Irritable bowel syndrome
Irritable bowel syndrome is a diagnosis of exclusion. It is a functional bowel disorder characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any detectable organic cause. In some cases, the symptoms are relieved by bowel movements...

,
and may include anaphylaxis
Anaphylaxis
Anaphylaxis is defined as "a serious allergic reaction that is rapid in onset and may cause death". It typically results in a number of symptoms including throat swelling, an itchy rash, and low blood pressure...

.

Food intolerance has been found associated with; irritable bowel syndrome
Irritable bowel syndrome
Irritable bowel syndrome is a diagnosis of exclusion. It is a functional bowel disorder characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any detectable organic cause. In some cases, the symptoms are relieved by bowel movements...

 and inflammatory bowel disease
Inflammatory bowel disease
In medicine, inflammatory bowel disease is a group of inflammatory conditions of the colon and small intestine. The major types of IBD are Crohn's disease and ulcerative colitis.-Classification:...

, chronic constipation, chronic hepatitis C infection, eczema, NSAID intolerance, respiratory complaints, including asthma, rhinitis and headache, functional dyspepsia, eosinophilic esophagitis and ENT illnesses.

Causes

Reactions to chemical components of the diet are more common than true food allergies. They are caused by various organic chemicals occurring naturally in a wide variety of foods, both of animal and vegetable origin more often than to food additives, preservatives, colourings and flavourings, such as sulfite
Sulfite
Sulfites are compounds that contain the sulfite ion SO. The sulfite ion is the conjugate base of bisulfite. Although the acid itself is elusive, its salts are widely used.-Structure:...

s or dyes. Both natural and artificial ingredients may cause adverse reactions in sensitive people if consumed in sufficient amount, the degree of sensitivity varying between individuals.

Pharmacological responses to naturally occurring compounds in food, or chemical intolerance, can occur in individuals from both allergic and non-allergic family backgrounds. Symptoms may begin at any age, and may develop quickly or slowly. Triggers may range from a viral infection or illness to environmental chemical exposure. It occurs more commonly in women, which may be because of hormone differences, as many food chemicals mimic hormones.

A deficiency in digestive enzymes can also cause some types of food intolerances. Lactose intolerance
Lactose intolerance
Lactose intolerance, also called lactase deficiency or hypolactasia, is the inability to digest and metabolize lactose, a sugar found in milk...

 is a result of the body not producing sufficient lactase
Lactase
Lactase , a part of the β-galactosidase family of enzymes, is a glycoside hydrolase involved in the hydrolysis of the disaccharide lactose into constituent galactose and glucose monomers...

 to digest the lactose in milk; dairy foods which are lower in lactose, such as cheese, are less likely to trigger a reaction in this case. 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.

The most widely distributed naturally occurring food chemical capable of provoking reactions is salicylate, although tartrazine
Tartrazine
Tartrazine is a synthetic lemon yellow azo dye used as a food coloring...

 and benzoic acid
Benzoic acid
Benzoic acid , C7H6O2 , is a colorless crystalline solid and the simplest aromatic carboxylic acid. The name derived from gum benzoin, which was for a long time the only source for benzoic acid. Its salts are used as a food preservative and benzoic acid is an important precursor for the synthesis...

 are well recognised in susceptible individuals. Benzoates and salicylates occur naturally in many different foods, including fruits, juices, vegetables, spices, herbs, nuts, tea, wines, and coffee. Salicylate sensitivity
Salicylate sensitivity
Salicylate sensitivity, also known as salicylate intolerance, is any adverse effect that occurs when a normal amount of salicylate is introduced into a person's body...

 causes reactions to not only aspirin and NSAIDs but also foods in which salicylates naturally occur, 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.

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.

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 occur when foods containing the triggering substance are eaten in a combined quantity that exceeds the patient's sensitivity thresholds. People with food sensitivities have different sensitivity thresholds, and so more sensitive people will react to much smaller amounts of the substance.

Pathogenesis

The term food allergy is widely misused for all adverse reactions to food. Food allergy (FA) is a food hypersensitivity occurring in susceptible individuals, which is mediated by a classical immune mechanism specific for the food itself. The best established mechanism in FA is due to the presence of IgE antibodies against the offending food. Food intolerance (FI) are all other adverse reactions to food. Subgroups of FI are 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). As knowledge of mechanisms and causes of food intolerance improve, nomenclature will be updated. There is no worldwide scientific consensus on the pathogenesis of food intolerance.

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), among other metabolic, pharmacological and digestive abnormalities.

A frequent misconception among the general public is confusion between cow's milk allergy (CMA) and cow’s milk intolerance, which is usually intolerance to lactose. There are at least two, and possibly more, distinct pathologies. Hypersensitivity to milk is often broadly classified into immunoglobulin E (IgE)-mediated allergy and non-IgE-mediated intolerance. The immunopathological mechanisms of non-IgE-mediated intolerance in particular remain poorly understood, and this has hindered the development of simple and reliable diagnostics. Adults with non-IgE-mediated intolerance to milk tend to suffer ongoing reactions without the development of tolerance. The precise immunopathological mechanisms of non-IgE-mediated intolerance remain unclear. A number of mechanisms have been implicated, including type-1 T helper cell (Th1) mediated reactions, the formation of immune complexes leading to the activation of Complement, or T-cell/mast cell/neuron interactions inducing functional changes in smooth muscle action and intestinal motility. Food antigens contact the immune system throughout the intestinal tract via the gut associated lymphoid system (GALT), where interactions between antigen presenting cells and T cells direct the type of immune response mounted. Unresponsiveness of the immune system to dietary antigens is termed "oral tolerance" and is believed to involve the deletion or switching off of reactive antigen-specific T cells and the production of regulatory T cells (T reg) that quell inflammatory responses to benign antigens. In the case of IgE-mediated allergies, a deficiency in regulation and a polarisation of specific effector T cells towards type-2 T helper cells (Th2) lead to signalling of B-cells to produce milk protein-specific IgE. Where as non-IgE-mediated reactions (intolerances) may be due to Th1 mediated inflammation. Dysfunctional T reg cell activity has been identified as a factor in both allergy/ intolerance mechanisms.

Diagnosis

Diagnosis of food intolerance can include hydrogen breath test
Hydrogen Breath Test
A hydrogen breath test is used as a clinical medical diagnosis for people with irritable bowel syndrome, and common food intolerances. The test is simple, non-invasive, and is performed after a short period of fasting . Even though the test is normally known as a "Hydrogen Breath Test" some...

ing for lactose intolerance
Lactose intolerance
Lactose intolerance, also called lactase deficiency or hypolactasia, is the inability to digest and metabolize lactose, a sugar found in milk...

 and fructose malabsorption
Fructose malabsorption
Fructose malabsorption, formerly named "dietary fructose intolerance," is a digestive disorder in which absorption of fructose is impaired by deficient fructose carriers in the small intestine's enterocytes. This results in an increased concentration of fructose in the entire intestine.Fructose...

, professionally supervised elimination diet
Elimination diet
An elimination diet is a method of identifying foods that an individual cannot consume without adverse effects. Adverse effects may be due to food allergy, food intolerance, other physiological mechanisms , or a combination of these...

s, and ELISA testing for IgG-mediated immune responses to specific foods. It is important to be able to distinguish between food allergy, food intolerance, and autoimmune disease in the management of these disorders. Non-IgE-mediated intolerance is more chronic, less acute, less obvious in its clinical presentation, and often more difficult to diagnose than allergy, as skin tests and standard immunological studies are not helpful. Elimination diets must remove all poorly tolerated foods, or all 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.

The antigen leukocyte cellular antibody test (ALCAT) has been commercially promoted as an alternative, but has not been reliably shown to be of clinical value.

Testing of IgG4 to foods can be performed in the laboratory work-up of food intolerance. IgG4 against foods indicates that the person has been repeatedly exposed to food proteins recognized as foreign by the immune system. According to one review, its presence should not be considered a factor which induces hypersensitivity, but rather as an indicator for immunological tolerance, linked to the activity of T cells. It concludes food-specific IgG4 does not indicate (imminent) food allergy or intolerance, but rather a physiological response of the immune system after exposure to food components. However elimination of IgG-mediated poorly tolerated foods from the diet of IBS patients resulted in an improvement in symptoms.

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.
Treatment can involve long-term avoidance, or if possible re-establishing a level of tolerance.

Prevention

There is emerging evidence from studies of cord bloods that both sensitization and the acquisition of tolerance can begin in pregnancy, however the window of main danger for sensitization to foods extends prenatally, remaining most critical during early infancy when the immune system and intestinal tract are still maturing. 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.

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. 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.

Management

Individuals can try minor changes of diet to exclude foods causing obvious reactions, and for many this may be adequate without the need for professional assistance. For reasons mentioned above foods causing problems may not be so obvious since food sensitivities may not be noticed for hours or even days after one has digested food. Persons unable to isolate foods and those more sensitive or with disabling symptoms should seek expert medical and dietitian help. The dietetic department of a teaching hospital
Teaching hospital
A teaching hospital is a hospital that provides clinical education and training to future and current doctors, nurses, and other health professionals, in addition to delivering medical care to patients...

 is a good start. (see links below)

Guidance can also be given to your general practitioner to assist in diagnosis and management. Food elimination diet
Elimination diet
An elimination diet is a method of identifying foods that an individual cannot consume without adverse effects. Adverse effects may be due to food allergy, food intolerance, other physiological mechanisms , or a combination of these...

s have been designed to exclude food chemicals likely to cause reactions and foods commonly causing true allergies and those foods where enzyme deficiency cause symptoms. These elimination diet
Elimination diet
An elimination diet is a method of identifying foods that an individual cannot consume without adverse effects. Adverse effects may be due to food allergy, food intolerance, other physiological mechanisms , or a combination of these...

s are not everyday diets but intended to isolate problem foods and chemicals. Avoidance of foods with additives is also essential in this process.

Individuals and practitioners need to be aware that during the elimination process patients can display aspects of food addiction, masking, withdrawals, and further sensitization and intolerance. Those foods that an individual considers as 'must have every day' are suspect addictions, this includes tea, coffee, chocolate and health foods and drinks, as they all contain food chemicals. Individuals are also unlikely to associate foods causing problems because of masking or where separation of time between eating and symptoms occur. The elimination process can overcome addiction and unmask problem foods so that the patients can associate cause and effect.

It takes around five days of total abstinence to unmask a food or chemical, during the first week on an elimination diet
Elimination diet
An elimination diet is a method of identifying foods that an individual cannot consume without adverse effects. Adverse effects may be due to food allergy, food intolerance, other physiological mechanisms , or a combination of these...

 withdrawal symptoms can occur but it takes at least two weeks to remove residual traces. If symptoms have not subsided after six weeks, food intolerance is unlikely to be involved and a normal diet should be restarted. Withdrawals are often associated with a lowering of the threshold for sensitivity which assists in challenge testing, but in this period individuals can be ultra-sensitive even to food smells so care must be taken to avoid all exposures.

After two or more weeks if the symptoms have reduced considerably or gone for at least five days then challenge testing can begin. This can be carried out with selected foods containing only one food chemical, so as to isolate it if reactions occur. In Australia, purified food chemicals in capsule form are available to doctors for patient testing. These are often combined with placebo
Placebo
A placebo is a simulated or otherwise medically ineffectual treatment for a disease or other medical condition intended to deceive the recipient...

 capsules for control purposes. (See link below.) This type of challenge is more definitive. New challenges should only be given after 48 hours if no reactions occur or after five days of no symptoms if reactions occur.

Once all food chemical sensitivities are identified a dietitian
Dietitian
Dietitians supervise the preparation and service of food, develop modified diets, participate in research, and educate individuals and groups on good nutritional habits. The goals of dietitians are to provide medical nutritional intervention, and to obtain, safely prepare, serve and advise on...

 can prescribe an appropriate diet for the individual to avoid foods with those chemicals. Lists of suitable foods are available from various hospitals and patient support groups can give local food brand advice. A dietitian will ensure adequate nutrition is achieved with safe foods and supplements if need be.

Over a period of time it is possible for individuals avoiding food chemicals to build up a level of resistance by regular exposure to small amounts in a controlled way, but care must be taken, the aim being to build up a varied diet with adequate composition.

Prognosis

The prognosis of children diagnosed with intolerance to milk is good: patients respond to diet which excludes cow's milk protein and the majority of patients succeed in forming tolerance. Children with non-IgE-mediated cows milk intolerance have a good prognosis, whereas children with IgE-mediated cows milk allergy in early childhood have a significantly increased risk for persistent allergy, development of other food allergies, asthma and rhinoconjunctivitis.

A study has demonstrated that identifying and appropriately addressing food sensitivity in IBS patients not previously responding to standard therapy results in a sustained clinical improvement and increased overall well being and quality of life.

Epidemiology

Estimates of the prevalence of food intolerance vary widely from 2% to over 20% of the population. So far only three prevalence studies in Dutch and English adults have been based on double-blind, placebo-controlled food challenges. The reported prevalences of food allergy/intolerance (by questionnaires) were 12% to 19%, whereas the confirmed prevalences varied from 0.8% to 2.4%. For intolerance to food additives the prevalence varied between 0.01 to 0.23%.

Food intolerance rates were found to be similar in the population in Norway. Out of 4,622 subjects with adequately filled-in questionnaires, 84 were included in the study (1.8%) Perceived food intolerance is a common problem with significant nutritional consequences in a population with IBS. Of these 59 (70%) had symptoms related to intake of food, 62% limited or excluded food items from the diet.
Tests were performed for food allergy and malabsorption, but not for intolerance. There were no associations between the tests for food allergy and malabsorption and perceived food intolerance, among those with IBS. Perceived food intolerance was unrelated to musculoskeletal pain and mood disorders.

According to the RACP working group, "Though not considered a "cause" of CFS, some patients with chronic fatigue report food intolerances that can exacerbate symptoms."

History

In 1978 Australian researchers published details of an 'exclusion diet' to exclude specific food chemicals from the diet of patients. This provided a basis for challenge with these additives and natural chemicals. Using this approach the role played by dietary chemical factors in the pathogenesis of chronic idiopathic urticaria (CIU) was first established and set the stage for futute DBPCT trials of such substances in food intolerance studies.

In 1995 the European Academy of Allergology and Clinical Immunology suggested a classification on the basis of the responsible pathogenetic mechanism; according to this classification, non-toxic reactions can be divided into 'food allergies' when they recognize immunological mechanisms, and 'food intolerances' when there are no immunological implications. Reactions secondary to food ingestion are defined generally as 'adverse reactions to food'.

In 2003 the Nomenclature Review Committee of the World Allergy Organization issued a report of revised nomenclature for global use on food allergy and food intolerance, that has had general acceptance. Food intolerance is described as a 'non allergic hypersensitivity' to food.

Society and culture

In the UK, scepticism about food intolerance as a specific condition influenced doctors' (GPs') perceptions of patients and of the patients' underlying problems. However, rather than risk damaging the doctor-patient relationship
Doctor-patient relationship
The doctor-patient relationship is central to the practice of healthcare and is essential for the delivery of high-quality health care in the diagnosis and treatment of disease. The doctor-patient relationship forms one of the foundations of contemporary medical ethics...

, when GPs chose, despite their scepticism, and tempered by an element of awareness of the limitations of modern medicine, to negotiate mutually acceptable ground with patients and with patients' beliefs. That as a result, whether due to a placebo effect, secondary benefit, or as a biophysical result of excluding a food from the diet, the GPs acknowledged benefit, both personal and therapeutic.

In the Netherlands, patients and their doctors (GPs) have different perceptions of the efficacy of diagnostic and dietary interventions in IBS. Patients consider food intolerance and GPs regard lack of fibre as the main etiologic dietary factor. GPs should explore the patients' expectations and incorporate these in their approach to IBS patients.

New food labeling regulations were introduced into the USA and Europe in 2006, which are said to benefit people with intolerances. In general, food-allergic consumers were not satisfied with the current labelling practices.
In the USA food companies propose distinguishing between food allergy and food intolerance and use a mechanism-based (i.e., immunoglobulin-E-mediated), acute life-threatening anaphylaxis that is standardized and measurable and reflects the severity of health risk, as the principal inclusion criterion for food allergen labeling. Symptoms due to, or exacerbated by, food additives usually involve non-IgE-mediated mechanisms (food intolerance) and are usually less severe than those induced by food allergy, but can include anaphylaxis.

Research directions

A Low FODMAP diet now has an evidence base sufficiently strong to recommend its widespread application in conditions such as IBS
Irritable bowel syndrome
Irritable bowel syndrome is a diagnosis of exclusion. It is a functional bowel disorder characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any detectable organic cause. In some cases, the symptoms are relieved by bowel movements...

 and IBD
Inflammatory bowel disease
In medicine, inflammatory bowel disease is a group of inflammatory conditions of the colon and small intestine. The major types of IBD are Crohn's disease and ulcerative colitis.-Classification:...

. Restriction of Fermentable Oligo-, Di- and Mono-
saccharides and Polyols globally, rather than individually, controls the symptoms of functional gut disorders (e.g. IBS), and the majority of IBD patients respond just as well. It is more successful than restricting only Fructose and Fructans, which are also FODMAPs, as is recommended for those with Fructose malabsorption
Fructose malabsorption
Fructose malabsorption, formerly named "dietary fructose intolerance," is a digestive disorder in which absorption of fructose is impaired by deficient fructose carriers in the small intestine's enterocytes. This results in an increased concentration of fructose in the entire intestine.Fructose...

. Longer term compliance with the diet was high.

A randomised controlled trial on IBS patients found relaxing an IgG-mediated food intolerance diet led to a 24% greater deterioration in symptoms compared to those on the elimination diet and concluded food elimination based on IgG antibodies may be effective in reducing IBS symptoms and is worthy of further biomedical research.

Intestinal or bowel hyperpermeability, so called leaky gut
Leaky gut
Leaky gut is a name used to describe intestinal or bowel hyperpermeability. Tight junctions represent the major barrier within the pathway between intestinal epithelial cells that line the digestion tract...

, has been linked to food allergies and some food intolerances. Research is currently focussing on specific conditions and effects of certain food constituents. At present there are a number of ways to limit the increased permeability, but additional studies are required to assess if this approach reduces the prevalence and severity of specific conditions.

See also

  • Sucrose intolerance
    Sucrose intolerance
    Sucrose intolerance, also called congenital sucrase-isomaltase deficiency or Sucrase-isomaltase deficiency, is the condition in which sucrase, an enzyme needed for proper metabolization of sucrose, is not produced in the small intestine....

  • Fructose intolerance
  • Fructose malabsorption
    Fructose malabsorption
    Fructose malabsorption, formerly named "dietary fructose intolerance," is a digestive disorder in which absorption of fructose is impaired by deficient fructose carriers in the small intestine's enterocytes. This results in an increased concentration of fructose in the entire intestine.Fructose...

  • Citric acid intolerance
    Citric acid intolerance
    Citric acid intolerance is a little-known type of food intolerance in which sufferers report various symptoms in response to foods or other products containing citric acid that they attribute neither to its properties as an acid nor to an Aspergillus niger hypersensitivity...

  • Lactose intolerance
    Lactose intolerance
    Lactose intolerance, also called lactase deficiency or hypolactasia, is the inability to digest and metabolize lactose, a sugar found in milk...

  • Gluten sensitivity
    Gluten sensitivity
    Gluten sensitivity belongs to a spectrum of disorders in which gluten has an adverse effect on the body. It can be defined as a non-allergic and non-autoimmune condition in which the consumption of gluten can lead to symptoms similar to those observed in coeliac disease or wheat allergy .Gluten...

    • Gluten-sensitive enteropathy
  • Salicylate sensitivity
    Salicylate sensitivity
    Salicylate sensitivity, also known as salicylate intolerance, is any adverse effect that occurs when a normal amount of salicylate is introduced into a person's body...

  • Sodium phosphates
    Sodium phosphates
    Sodium phosphate is a generic term for the salts of sodium hydroxide and phosphoric acid. They are:* sodium dihydrogen phosphate, commonly termed monosodium phosphate, , is also known as "sodium phosphate, monobasic"....

  • Drug intolerance
    Drug intolerance
    Drug intolerance or drug sensitivity is a lower threshold to the normal pharmacologic action of a drug. It is not to be confused with drug allergy. Drug intolerance is uncommon and idiopathic, thus extremely difficult to predict except in persons with a prior history or a family history of...

  • Elimination diet
    Elimination diet
    An elimination diet is a method of identifying foods that an individual cannot consume without adverse effects. Adverse effects may be due to food allergy, food intolerance, other physiological mechanisms , or a combination of these...


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