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Food allergies and food sensitivities

The Institute of Food Technologists has updated its Scientific Status Summary on food allergies and other food sensitivities. The new version which is very comprehensive and extensively referenced appears in Food Technology 55 2001 68-83. [A PDF version is available from IFT's website.] Readers with a special interest in this field are advised to consult the whole summary. Some of the main points are discussed below.

Authorities world wide are responding to consumer concerns and are increasing labelling requirements with regard to potential allergens. Responsible manufacturers have initiated their own programs to prevent the risk of cross-contamination of manufactured foodstuffs with allergens by dedication of process lines or specific pieces of equipment, appropriate scheduling of manufacturing operations and effective clean up between operations. The authors of the summary reference a series of their own papers in the journal Food Allergy and Intolerance which describe good manufacturing practice in this regard. A web address for the US National Food Processors Association's Code of Practice on managing food allergens is also provided: http://www.nfpa-food.org/news/040901%20CodeofPracticeBrochure.htm

Adverse reactions to food

The authors commence their summary by pointing out that true food allergies represent a fraction only of the individual adverse reactions to foods which they group into a number of main categories.

They stress the importance of accurate labelling and of the avoidance of contact between allergenic and non-allergenic foods during preparation.

True food allergies

True food allergies are abnormal responses of the immune system to components of certain foods. The components of foods that elicit these abnormal responses are typically naturally occurring proteins in foods. True food allergies can be divided into immediate hypersensitivity reactions, where symptoms develop within minutes or hours after ingestion of the offending food, and delayed hypersensitivity reactions where symptoms do not appear for 24 hours or longer after ingestion of the food.

The antigens which provoke the immune response are proteins but only a few of the many proteins in nature are capable of stimulating the production of specific immuno-globulin E (IgE) antibodies. Because foods are ingested, gastrointestinal symptoms are the most common although skin and respiratory tract reactions can occur. Although few asthmatic individuals experience food-induced asthma, asthma is among the most severe symptoms associated with food allergies. It can be a life threatening reaction.

The most alarming symptom associated with food allergies is anaphylactic shock. Death can occur within minutes of ingestion of the offending food from cardiovascular and/or respiratory collapse. Only a few of the many people with IgE mediated food allergies are at risk of such serious manifestations.

True food allergies are estimated to affect between 2 and 2.5 per cent of the population (in the United States). Infants and children are more commonly affected than other age groups (5-8 per cent). Most food allergies developed in infancy are outgrown in early childhood. Allergies to foods such as cows' milk, eggs and soybeans are much more likely to be outgrown than allergies to other foods such as peanuts which are almost never outgrown.

Most common allergenic foods

The frequency of occurrence of allergies to specific foods is not known. Eight foods or food groups are thought to account for more than 90 per cent of all IgE mediated food allergies on a world wide basis. These groups are: milk, eggs, fish, crustacea, peanuts, soybeans, tree nuts, and wheat. More than 160 other foods have been documented as causing food allergies less frequently.

The proteins which constitute the food allergens are usually stable to heat processing so that heat processed forms of commonly allergenic foods often retain their allergenicity. If the protein fraction is removed during processing, the resulting product or ingredient may be safe because the allergen has been removed. The best example of this is the production of edible oils from peanuts and soybeans. The precise threshold doses for allergenic foods have not been carefully investigated and probably vary from one allergic individual to another. In one investigation using peanut protein with sensitive individuals, the most sensitive of 12 subjects experienced an objective reaction to 2 milligrams of peanut protein.

Anecdotal evidence would support the view that the threshold level at least for peanut protein is very low. A specific avoidance diet is the only prophylactic approach to the treatment of food allergies. The construction of safe and effective diets is often a challenge for individuals with food allergies. Exposure to very small amounts of an offending food may be sufficient to elicit allergic reactions and this may pose a particular problem in food service situations where foods are not labelled and may be subject to inadvertent cross contamination.

Non-IgE cell mediated reactions

These are the delayed hypersensitivity reactions noted above. They have an onset time of 6-24 hours after ingestion of the offending food. The role of non-IgE cell mediated reactions in food allergies remains somewhat uncertain but mounting evidence indicates that coeliac disease occurs through this mechanism.

Coeliac disease is a malabsorption syndrome occurring in sensitive individuals after the consumption of wheat, rye, barley, triticale, and perhaps other related species. A fraction of the grain, the gliadin fraction, is associated with the initiation of coeliac disease in susceptible individuals. Treatment again involves avoidance of the implicated foods.

Food intolerances

Food intolerances are abnormal reactions to foods or food components that do not involve the immune system. The main intolerances can be classified as metabolic food disorders and idiosyncratic reactions.

Metabolic food disorders. Lactose intolerance is an example of a metabolic food disorder resulting from a genetic deficiency in the host's ability to metabolise lactose.

Lactose is a disaccharide and the principal sugar in milk. Normally lactose is broken up to its constituent monosaccharides, glucose and galactose, in the small intestine. In lactose intolerance, the activity level of β–galactosidase, the metabolic enzyme primarily responsible for splitting the lactose molecule is diminished. Undigested lactose passes into the colon where the colonic bacteria metabolise the lactose to carbon dioxide, hydrogen and water. Abdominal cramping, flatulence and diarrhoea are the resulting symptoms of lactose intolerance.

The disorder is especially prevalent in some ethnic groups and tends to worsen with advancing age. Avoidance of dairy products containing lactose is the only method of control although some affected individuals can tolerate some lactose in the diet.

Favism is another example of a metabolic disorder stemming from an inherited deficiency in the enzyme, glucose-6- phosphate dehydrogenase. Symptoms occur after consumption of fava beans and in severe cases can lead to haemolytic anaemia. Fava beans are not frequently eaten outside Mediterranean and Middle East countries and the illness is promptly resolved when the beans are removed from the diet.

Idiosyncratic illnesses. Some adverse reactions to foods are described in this way because the mechanism for the illnesses is unknown.

The role of specific foods or ingredients is firmly established in only a few of the many alleged foodborne idiosyncratic reactions. Sulphite induced asthma is perhaps the best example.

Although sulphites have been used in food systems for centuries, they have been implicated as triggers of asthma in some sensitive individuals only relatively recently. The reaction usually occurs within a few minutes of the ingestion of a provoking dose of sulphite. It can be severe on occasion and deaths have been attributed to sulphite induced asthma. Existing labelling regulations reflect the fact that the ingestion of smaller amounts of sulphite presents a lesser risk.

Several different mechanisms have been proposed for this reaction but none has been proven.

The authors of the summary also discuss some other reported alleged food idiosyncrasies but give them little credence. They dismiss the so-called Feingold Theory which links artificial food colours to hyperkinesis as proved to be not valid. They also question the role of monosodium glutamate in either the 'Chinese Restaurant Syndrome' (MSG Symptom Complex) or the provocation of asthma.

Communicating with consumers

Although specific food allergies and intolerances cause adverse reactions in only a small proportion of consumers, collectively they affect a significant number of people. Susceptible people must modify their lifestyles and eating practices in order to avoid unwittingly consuming foods and food ingredients which may adversely affect them, or even prove life threatening. These people are largely dependent on the food industry to provide them with accurate ingredient labelling and safe food manufacturing processes that eliminate the risk of undeclared residues of allergenic foods being incorporated in other products.

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Prepared by Keith Richardson and Beverley George
Food Science Australia
PO Box 52, North Ryde 1670. Tel +61 2 9490 8397 Fax +61 2 9490 8499
Email enquiries@csiro.au