Many patients ascribe their 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, e.g. urticaria, vomiting or diarrhoea after eating 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 childrenhas been successfully treated by removal of eggs from the diet suggesting some form of food allergy.
RHINITIS AND ASTHMA have been produced by foods such as milk and chocolate, mainly in atopic subjects; again suggesting some food allergy.
CHRONIC URTICARIA. This has been successfully treated by exclusion diet.
MIGRAINE. In some subjects this seems to be triggered by foods such as chocolate, cheese and alcohol suggesting a trigger mechanism, although probably not a true allergic phenomenon.
In addition, some people suffer reactions 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 favabean-induced haemolytic anaemia in glucose-e-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, irritable bowel syndrome and Crohn’s disease are due to food ingestion.
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.
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 valueless and possibly fraudulent. Diagnostic exclusion diets are sometimes used, but these are time consuming, although can occasionally be of value in identifying a particular food causing problems.
DIETARY CHALLENGE is used when the food and the test is given sublingually or by inhalation to try andreproduce 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 good scientific evidence to support these exclusion diets is non-existent.