Food allergies and intolerances

Food intolerances

Other types of immune reactions are responsible for the less catastrophic symptoms of intolerance, such as itching, runny nose, headache, catarrh, fatigue and flare-ups of conditions such as eczema, asthma, psoriasis, arthritis and irritable bowel syndrome. These reactions, which may involve delayed white blood cell responses, or another type of antibody, known as IgG, tend to come on more slowly - usually several hours or even days after eating culprit foods. This delay makes it difficult to identify the items to which you have become sensitised. The types of food intolerance that are medically accepted include:

Lactose intolerance - due to the inability to digest lactose sugar in milk, causing bloating, abdominal pain and diarrhoea in those not producing sufficient amounts of the enzyme, lactase.

Gluten intolerance - an autoimmune condition in which sensitivity to a protein (gliadin) found in wheat and some other cereals causes bloating, abdominal pain, bulky stools and weight loss (coeliac disease).

Hypersensitivity - in which a widespread, itchy rash (urticaria), eczema, asthma, vomiting, abdominal pains or diarrhoea can occur through eating certain foods. In some cases, these are due to high levels of naturally-occurring histamine found in foods such as tuna, strawberries, fermented foods, tomatoes, cheese, aubergine and citrus fruits.

Other drug-like reactions - in which chemicals such as monosodium glutamate, sulphites, salicylates, benzoates, tartrazine and tyramine present in certain foods can trigger symptoms such as asthma or migraine.

Identifying the foods that upset you

• simple exclusion, with the elimination of a single food such as eggs


• multiple exclusion - elimination of several foods that have been linked with a particular problem
• restriction diet - which consists of eating very few foods eg nothing but a single meat (eg lamb), a single source of carbohydrate (eg rice), a single fruit (eg pears) and drinking spring, mineral or distilled water.

After following the elimination diet until symptoms have disappeared (commonly 10 - 21 days) the eliminated foods are reintroduced one by one, usually at three day intervals, to see which triggers a recurrence. You will need to keep a careful food and symptom diary during this time, to help recognise which particular foods - if any - are triggering your symptoms. If an adverse reaction occurs, you continue to avoid the test food and wait 48 hours after all symptoms have improved before testing another food. If your symptoms are not significantly improved by following a restricted diet, it is important to return to eating a normal diet, and to eating as wide a range of foods as possible, to guard against nutrient deficiencies. If you are able to identify a small number of foods that undoubtedly provoke your symptoms, however, these can usually be avoided without affecting your overall nutrition.

Following an elimination and challenge diet is time consuming and sticking to it for several weeks is difficult. Blood tests that identify raised levels of specific anti-food antibodies, or which analyse the reaction of live white blood cells to purified food extracts can often provide a shortcut to identifying trigger foods.

Treatment
If you can identify which foods upset you, the best treatment is prevention - avoid these foods totally. If your food allergy causes potentially life-threatening reactions, it is important to carry antihistamines and an adrenaline injection (eg Epipen) with you so treatment can be started immediately before medical help arrives.