Many people ascribe their various symptoms to food allergy or food sensitivity, and there are a number of clinics in the UK where such sufferers are seen and started on exclusion diets. The scientific evidence that food does harm in most instances is incomplete, but certainly some evidence supports the following disease 'entities':
Acute hypersensitivity - Some patients develop acute reactions to a particular food; an example is urticaria, vomiting or diarrhoea after eating nuts, strawberries or shellfish. These reactions are presumably immunological hypersensitivity reactions mediated by IgE. This is usually not a clinical problem as the patients have already learned to avoid the suspected food.
Eczema and asthma - Particularly in young children, these have sometimes been treated successfully by removal of eggs from the diet, suggesting some form of food allergy.
Rhinitis and asthma - These have been produced by foods such as milk and chocolate, mainly in atopic subjects, again suggesting a food allergy.
Chronic urticaria - This has been treated successfully by an exclusion diet.
Migraine - In some subjects this seems to follow the intake of foods such as chocolate, cheese and alcohol, suggesting a trigger mechanism, although probably not a true allergic phenomenon.
Irritable bowel syndrome - In some patients this seems to be related to ingestion of certain food items, such as wheat, but the mechanisms are not clearly defined.
In addition, some people suffer a reaction due to a constituent of food (e.g. the histamine in mackerel or canned food, or the tyramine in cheeses), chemical mediators released by food (e.g. histamine may be released by tomatoes or strawberries), toxic chemicals found in food (e.g. the food additive tartrazine), an enzyme deficiency (e.g. milk-induced diarrhoea in alactasia or fava-bean-induced haemolytic anaemia in glucose-6-phosphate dehydrogenase deficiency).
Many other additives and compounds with certain E numbers have been implicated as causing reactions, but here the evidence is less than complete.
There is little or no evidence to suggest that diseases such as arthritis, behaviour and affective disorders and Crohn's disease are due to ingestion of a particular food.
Multiple vague symptoms such as tiredness or malaise are also not due to food allergy. Most of the patients in this group are suffering from a psychiatric disorder.
Management of Food allergy and food intolerance
A careful history may help to delineate the causative agent, particularly when the effects are immediate.
Skin-prick testing with allergen and measurement in the serum of antigen or antibodies have not correlated with symptoms and are usually misleading. 'Fringe' techniques such as hair analysis, although widely advertised, are of limited value.
Diagnostic exclusion diets are sometimes used, but they are time-consuming. They can occasionally be of value in identifying a particular food causing problems.
Dietary challenge consists of the food and the test being given sublingually or by inhalation in an attempt to reproduce the symptoms. Again this may be helpful in a few cases.
Most people who have acute reactions to food realize it and stop the food, and do not require medical attention. In the remainder of patients, a small minority seem to be helped by modifying their diet, but there is no good scientific evidence to support these exclusion diets.