Despite recent advances in our knowledge of immune processes involved in food allergy and intolerance, there have been few major developments in the treatment of this common condition. Avoidance of the offending food remains the mainstay of treatment. Pharmacological therapy is useful in acute reaction due to inadvertent exposure but generally disappointing in the treatment of chronic food intolerance.
The importance of a detailed history cannot be overstated. The diagnosis can often be made on the history alone. A dietary history helps to identify the consumption of the offending food and aids in suggesting replacement. Patients with a history of acute allergic reaction to foods such as milk, egg, fish or nuts have to be extremely careful in consuming packaged food or when eating out. Packaged foods should be labelled clearly with the highly allergenic foods to reduce avoidable morbidity and mortality.
In children with cow's milk intolerance, the development of relatively safer extensively hydrolysed formulae has been a welcome relief. However, the increasingly complicated processing of foods may unravel new food antigens. Indeed, the increase in the prevalence of allergic diseases in general and of food allergy in particular had been blamed on the drugs and fertilisers used by farmers and the addition of an ever-expanding list of preservatives used by the food industry. More recently there has been considerable debate on the usefulness or otherwise of genetically manipulated foods.
It is not always possible to make a confident diagnosis of food intolerance on history alone. A trial exclusion of the suspected food may lead to an improvement in symptoms. Careful monitoring of symptoms during the trial diet, preferably with the help of a symptom diary, is essential. A dietitian's services are invaluable in organising a trial exclusion diet. Where food intolerance is suspected and symptoms are severe but the food is not known, a trial of a few-foods or elemental diet may be warranted. The diagnosis should be confirmed by DBPCFC, where possible, before a longer period of avoidance is recommended, as placebo responses are not uncommon. The dietitian can also provide written and verbal explanation of the avoidance measures and ensure that the recommended diet is nutritionally adequate. Assessment by the dietitian may reveal a need for supplements of calcium, vitamins or a different source of protein or calories.
In children, allergy to multiple foods is common, and appropriate avoidance, in addition to replacement where necessary, leads to improvement in symptoms. This is usually self-limiting and children tend to grow out of the allergies. In adults, intolerance to multiple foods is rare. It is important that the avoidance diet contains alternative sources of protein and calories and appropriate supplements are provided. Prophylactic treatment with drugs such as antihistamine and cromoglycate is occasionally useful. Manipulation of the immune system to alter its response to food allergen specifically to a food (specific immunotherapy) has not been very successful. Non-specific immu-notherapy with peptide or DNA vaccines is being studied. An alternative approach is to reduce the antigenic component of the food to manufacture hypoallergenic foods.
Acute allergic reactions with life-threatening features are treated effectively with adrenaline. Patients at risk of these reactions should carry pre-loaded adrenaline at all times. Milder forms of acute reactions may respond to antihistamines. Prophylactic treatment of food allergy, to prevent an acute reaction, is not satisfactory. Recent development of drugs such as monoclonal antibodies to IgE, which inhibits all IgE-mediated allergic reactions, may prove to be useful in the prophylaxis of acute reactions or in the treatment of chronic food allergic symptoms.
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