| Food allergies and intolerances
Food allergies and food intolerances are becoming increasingly common, but how do you tell one from the other and are they really a problem? Although official figures suggest only two per cent of adults, and up to eight per cent of children have an accepted food allergy, as many as one in three people recognise that eating certain foods consistently triggers unwelcome symptoms. Food allergies Why allergies are more prevalent remains unknown. Most seem to result from ill-understood interactions between our immune system and our 21st-century diet, lifestyle and environment. One popular theory is that over cleanliness and excessive use of antibiotics has caused our 'T helper' immune cells to move away from anti-infective, antigen-tolerant reactions towards allergic type sensitivity reactions. Substances that trigger a classic allergic reaction are known as allergens and involve a type of antibody known as IgE. IgE interacts with immune cells in the skin, intestines and respiratory tract to cause the release of powerful chemicals, such as histamine. Foods that can trigger an Ig-E mediated 'classic' food allergy include:
In some people, these can cause a severe, life-threatening, anaphylactic reaction with falling blood pressure, constriction of airways, facial/tongue swelling and collapse. These symptoms tend to come on quickly, usually within minutes of exposure. 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 Traditionally, the foods to which you are allergic or intolerant are identified using an elimination and challenge diet to identify which products consistently cause symptoms when eaten. There are several degrees of exclusion diet ranging from:
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 |