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Food Intolerance

Implications of the term "food intolerance", with specific reference to:

1. Food Intolerance, Allergy and Aversion

Food Intolerance

Food intolerance is a reproducible, unpleasant (i.e. adverse) reaction to a specific food or food ingredient, and is not psychologically based. This occurs even when the affected person cannot identify the type of food which has been given.

Food Allergy

Food allergy is a form of food intolerance in which there is also evidence of an abnormal immunological reaction to the food.

Most true food allergies are of the type one (reagin dependent) type of allergy, and the reaction is IgE mediated.

Food Aversion

Food aversion comprises both psychological avoidance to food, when the subject avoids food for psychological reasons, and psychological intolerance, which is an unpleasant bodily reaction caused by emotions associated with food rather than the food itself. This does not occur when the food is given in an unrecognisable form.

2. Food Allergy

Food allergy predominantly affects very young children, and becomes less frequent with advancing age. In young children symptoms are related most commonly to the gastrointestinal tract, and to a lesser. extent the skin and respiratory tract. If the food allergic reaction is due to IgE antibodies, then these antibodies to the offending food protein can be demonstrated by skin testing or RAST testing of the blood.

Other forms of food intolerance may result from:

  1. food or food ingredients having an irritant effect in the gut, e.g., highly spiced curry
  2. a toxic effect, e.g., acetanilide in rape seed oil
  3. a pharmacological effect, e.g., monosodium glutamate
  4. an enzyme deficiency, e.g., lactase
  5. a histamine releasing effect in unsensitised individuals, e.g., shellfish
  6. the release of substances produced by the fermentation of food residues in the bowel.

3. Food Intolerance in Children

In children, if there is an associated atopic disorder, the symptoms provoked by food are likely to be due to genuine food allergy, but food intolerance is an appropriate teen if no immunological mechanism has been identified. Many of the symptoms of food intolerance are also present in the normal child, so diagnosis may be difficult.

The incidence of true food allergy is greatest in first few months of life, and decreases with age.

2 Many infants who are initially intolerant of certain foods undergo a complete resolution of their problem as they grow older. Resolution of hypersensitivity in infancy may occur in more than 40% of cases within - 2',! years.

There is no evidence as to whether children with food intolerance who are treated by diet fare any better in the long term than those continuing to ingest their offending foods.

Conditions caused by food intolerance include colic, posseting and vomiting, failure to thrive, diarrhoea, nappy rash, other rashes, and respiratory symptoms.

The disease spectrum of food intolerance and allergy in childhood also includes anaphylaxis, angiooedema and urticaria, coeliac disease, eczema, asthma and rhinitis, infantile colic, migraine and epilepsy, hyperactivity and essential reactive hypoglycaemia.

When the diagnosis of food intolerance is confirmed, children should avoid the offending foods for at least six months after the last symptomatic contact. It may then be possible to reintroduce small doses of the food under supervision.

4. Food Intolernace in Adults

The range of foods which could cause reactions in adults is extensive, and true allergy is specially related to eggs, nuts and fish, with symptoms such as asthma, eczema, angio-oedema and urticaria.

However, foods capable of producing the irritable bowel syndrome include wheat, corn, dairy products, coffee, tea and citrus fruits.

Milk and dairy products can cause either gastrointestinal symptoms or more widespread reactions, as do wheat and yeast products, soya and chocolate.

Early gastrointestinal symptoms include swelling of the lips, tingling of the mouth or throat, vomiting and pain. Late symptoms include diarrhoea, constipation, bloating and steatorrhoea.

Remote symptoms can include rhinorrhoea, urticaria, angio-oedema, anaphylaxis, asthma, eczema, headache and joint pains.

Migraine may be provoked by milk and cheese, fish, chocolate, oranges, alcohol, fatty fried food, vegetables (especially onions), tea and coffee.

5. Other Causes of Food Intolerance

Inborn errors of metabolism

Although inborn errors of metabolism are rare, those who are affected by them are often unable to metabolise one or more of the constituents of foods. Symptoms may arise because of the accumulation of toxic intermediates which cannot be processed through the normal metabolic pathways, or else because of a deficiency of essential nutrients.

Inborn errors of digestion and absorption may affect the digestion and absorption of carbohydrate, fat and protein.

Systemic disorders include disorders of amino acid and intermediary metabolism, hyperammonaemia and disorders of organic acid metabolism.

Disorders of carbohydrate metabolism include fructosaemia and galactosaemia. Disorders of fat metabolism include lipoprotein lipase deficiency.

There are other miscellaneous disorders of metabolism, including disorders of alcohol metabolism and glucose-6-phosphate dehydrogenase deficiency.

Pharmacological Reactions Associated with Foods

Many foods are capable of producing pharmacological effects which can be clinically important either if the food is take in large quantities, or if the patient tolerates it badly because of an enzyme defect or other biochemical variant.

Examples of these include caffeine in coffee and tea, and vasoactive amines, which are present in many foods including wine, cheese, yeast extracts, bananas and avocados. These chemicals include histamine, tryptophan, tyramine and serotonin.

There are also miscellaneous reactions to food, including monosodium glutamate (producing Kwok's syndrome, or the Chinese Restaurant syndrome), salt and lectins.

Adverse Reactions to Food Additives

A food additive is any substance not commonly regarded or used as food, which is added to, or used in or on, food.

Problems in this area include sensitivity to tartrazine and salicylates, and to sulphites.

6. Lactose Intolerance

Lactose intolerance is due to lactase deficiency, and two types of lactase deficiency are recognised, the congenital and the acquired forms.

Congenital lactase deficiency presents neonatally with profuse watery diarrhoea and collapse when milk feeds containing lactose are given. The condition is inherited and withdrawal of lactose can be lifesaving. The acquired type presents later, following a decline in lactase activity which occurs during childhood. In some ethnic groups the prevalence of this type of hypolactasia may reach 90%, but in Western European Caucasians it is less than 10%. This is thought to have a genetic basis, and not to be determined by environmental influences.

Hypolactasia may be suspected if diarrhoea, abdominal distention, discomfort and flatulence follow the ingestion of milk, but the symptoms could also be due to irritable bowel syndrome. Lactase deficiency can be diagnosed by giving a lactose load, observing the clinical response, and measuring stool sugars and breath hydrogen.

This may be confirmed by measurement of lactase activity in small intestinal mucosa. Symptoms should improve when lactose has been withdrawn from the diet. However, small amounts of lactose may still be able to be tolerated, especially as processed dairy foods.

7. Cows Milk Protein Intolerance

Cows milk protein allergy is commonest in infants. The main allergens can be casein, beta-lactoglobulin, or even the small amounts of bovine serum albumin present in the milk. More than one protein type can be involved.

The symptoms are mainly intestinal, with colic, loose mucous stools and abdominal discomfort. It usually develops only after some weeks of feeding cows milk. Heat treatment, as in making dried or evaporated milk, usually considerably reduces the risk of allergy, but pasteurisation uses to little heat to have an effect. Because of this, proprietary infant formulas, based on dried milk, are much less allergenic than diluted cows milk formulas.

Milk proteins can cause allergies in older children or adults, but the common belief that milk is inevitably "mucus forming" has been definitely disproved. Only if the individual has an allergy might it produce mucus.

Broadly speaking, milk allergic reactions can be divided into two groups, those which manifest quickly (i.e., within a few hours) after taking milk, and those in which the onset is delayed for many hours or even days. The quick onset reactions are usually easy to diagnose on historical grounds, and investigative techniques are helpful. However, the slow onset reactions are more difficult to recognise and to diagnose. Slow onset reactions may include cows milk sensitive enteropathy, cows milk-induced colitis, infantile colic, recurrent abdominal pain, protein losing enteropathy, and occult intestinal haemorrhage.

Cows milk enteropathy is associated with diarrhoea and irritability commencing usually within the first six months of life. There may also be vomiting. If milk feeding is continued, symptoms will persist with chronic diarrhoea and failure to thrive, and clinical features similar to coeliac disease. Most children at this stage have abnormal small intestinal mucosa demonstrated on biopsy, or abnormal intestinal function tests. However, unlike coeliac disease this enteropathy is not life long and two thirds of these children will tolerate cows milk without any problems by the time they are two years old.

Cows milk related colic is a very common problem in Western societies, and has been shown to be precipitated either directly or indirectly by milk ingestion.

Food sensitive colitis is relatively uncommon, and includes an explosive bloody diarrhoea which may be associated with shock and pallor. Protein losing enteropathy may occur with continued milk feeding in an infant in whom cows milk hypersensitivity is not recognised. Proteins leak into the intestinal lumen, resulting in hypoproteinanemia and peripheral oedema.

Occult intestinal haemorrhage can occur with whole fresh milk in some infants. This is a result of a heat labile fraction of one of the milk proteins, and a picture of iron deficiency anemia is seen. It can be managed by boiling the milk.

8. Reactivity to Sulphite Preservatives

Sulphiting agents include sulphur dioxide and sodium or potassium sulphite, bisulphite, and metabisulphite.

They are widely used in the food industry as preservatives to control microbial growth, and as antioxidants to prevent discolouration of foods.

They are marketed as vegetable freshness or potato whitening agents, and they may be added to commercially prepared foods. They are often used by restaurateurs to help preserve salads and seafood, and are also used in wine and beer preparation. Sulphites are not denatured by cooking.

Sulphite sensitivity is usually manifested as bronchospasm and sometimes as urticaria, angiooedema, gastrointestinal symptoms or anaphylactic shock.

Symptoms typically occur within a few minutes after inhalation of sulphur dioxide, and within 30 - 60 minutes after ingestion of a sulphite containing food.

The mechanism of sulphite sensitivity is not clear. Most subjects react only to inhaled sulphur dioxide, which is readily generated from sulphites, and an IgE mediated mechanism has been implicated in a few cases.

In some patients, the reactions have been attributed to a deficiency in the enzymes sulphite oxidase, and treatment with vitamin B 12 may provide protection.

Because many asthmatics can react with bronchospasm to sulphites added as food preservatives, especially to wines, all asthmatics should be cautioned to avoid any food or drink labeled with a sulphite or sulphur dioxide additive, the first two digits of which are "22".

9. Summary

Food intolerance is a condition in which there are reproducible adverse effects after ingesting a specific food or food ingredient.

Food intolerance includes the pattern of food allergy, in which there is a type 1 allergic response.

Food intolerance may also result from food or food ingredients having an irritant effect in the gut, toxic effect of foods, pharmacological effects, enzyme deficiency, histamine releasing effects, and release of substances produced by the fermentation of food residues in the bowel. It can also be due to additives in the food. Three examples of food intolerance include lactose intolerance, cows milk protein intolerance and reactivity to sulphite preservatives.

Bibliography

A Joint Report of the Royal College of Physicians and the British Nutrition Foundation. J. Roy. Coll. Phys. Lond. 18(2):83-123 (1984).

Position of the New Zealand Dietetic Association. The Nutritional Management of Food Intolerance Journal of the New Zealand Dietetic Association 43(2):57-66 1989.

Bahna, S.L. Food Sensitivity. Post Grad Med 82(5):195-205 (1987)

Ford, R Cow's Milk Intolerance and Feeding Problems. Patient Management, December 1987, 35-42.

Preedman, B.J. Asthma induced by sulphur dioxide, benzoate and tartrazine contained in orange drink. Chin. All. 7:407-415 (1977).

Lloyd A.G. et. al. Problems posed by essential food preservatives. Brit. Med. Bull 31(')):214-9 (1977)