Food allergy or intolerance is extremely common, with probably over 50% of the population having such problems, though extremely few realise it. Most people, however, understand allergies to infrequently eaten foods such as oysters, strawberries, peanuts, etc. which are usually obvious.

In contrast, masked food sensitivity develops insidiously and patients are totally unaware that they are reacting to everyday foods such as wheat, corn, milk, yeast, soy, sugar, tea, coffee and eggs. These sensitivities gradually develop rather in the same way as people start to develop hay fever, a reaction to grass pollens, which they have been in contact with for many years without any prior problem.

When patients eat these masked food allergens, the food initially makes them feel slightly improved and can often become quite addicted to whatever they are sensitive to. When a patient goes onto a diet that contains none of the foods to which they are sensitive, they feel worse for the first three or four days, due to the avoidance of these foods. This is termed a withdrawal reaction and proves the existence of a food sensitivity. After six or seven days they usually feel better than they have done for years. Huge numbers of patients lose symptoms such as fatigue, joint pains, headaches, migraines, irritable bowel syndrome, Crohn's Disease, muscle pains, asthma, eczema, urticaria and many other conditions. Usually 17 very safe foods are allowed on these diets, which if conclusive are followed by the selective reintroduction of other foods. Once a food has been avoided for seven days, adverse reactions become obvious on reintroduction, both to the patient and the doctor. Children tend to have fewer food intolerances than adults, and we often increase the number of foods allowed when investigating children

Elimination diets are widely used these days by allergy clinics and some paediatric and other hospitals.