If you have ever seen a victim of true food allergy after he or she has eaten an offending food, you will know that the reactions can be alarming! The lips swell up almost instantly and an itchy, raised red rash develops along with welts around the mouth. Sometimes the mouth becomes intensely itchy and the uvula (the small tongue at the back of the throat) may become swollen. The foods which most often cause this kind of reaction are eggs, nuts, shellfish, citru fruits and berries. Reactions in the lower part of the digestive tract take a little longer to develop but nausea and vomiting - often accompanied by sudden severe diarrhoea (sometimes with blood in the stools) - may occur within 30 minutes of eating seafood or eggs. This reaction may be followed by flushing, headaches, itching and palpitations which usually disappear after 2-4 hours. All in all, it can be a very unpleasant business!
Highly allergic people should carry an adrenaline inhaler with them at all times, but especially when eating out. If they feel an allergic reaction starting up, they should immediately take in between 3 and 6 puffs of the inhaler. This will prevent any tightness and swelling occurring in the throat. Immediately thereafter a rapidly acting antihistamine (such as Phenergan) 25mg tablet should be swallowed. In virtually all cases, this on-the-spot treatment will enable the affected person to reach medical attention in good time.
Foods may produce allergic reactions in other organs as well. For example, some people can have asthma attacks which may be just as severe as reactions caused by inhaling allergens such as dust or pollens. Allergy to foods may also worsen an existing allergic rash (urticaria) in other parts of the body. In one hospital study in Europe330 patients with recurrent urticaria (also known as hives or nettle rash) were asked what made their condition worse. Foods were said to worsen their skin rash in 30% of cases and 18% thought that drinks did the same. Fruits: vegetables, nuts and fish were the worst offenders.
The best way of looking at this aspect of food allergy is to divide the symptoms that occur into two groups - those that affect the digestive tract (by far the most common) and those that affect other parts of the body. It is important to stress that these symptoms are much more common in young infants and toddlers under 2 years of age than in older children and adults. In fact, there are few examples of food allergy persisting from infancy or early childhood into adult life and the vast majority of babies who are allergic to some foods outgrow their early sensitivity as their bowel matures.
Digestive symptoms
The immediate reactions which occur on contact with an allergenicfood have been discussed above, as have the other common reactions such as vomiting, diarrhoea, nausea and abdominal pain.
In studies on babies in London, doctors were struck by the fact that there seemed to be a link between putting the infants onto artificial feeds and the onset of colic and diarrhoea. It appeared to be mainly the large bowel that was affected and if the babies were taken off these feeds, their colitis (inflammation of the bowel) cleared rapidly. It was found that the major cause of the problem was cow's milk, though some of the babies had reactions to soya and beef proteins. To find out what was happening, a series of studies were done, using a tube with several well-positioned reflecting optics which allowed the inside of the large bowel to be seen clearly. What this showed was that there was noticeable inflammation of the wall of the colon, which disappeared when the offending food was withdrawn.
Food intolerance appears to be closely linked with the Irritable Bowel Syndrome (IBS) or 'spastic colon' which occurs in adults. In this uncomfortable condition, abdominal pain is accompanied by diarrhoea or constipation. In one research project 21 sufferers from IBS were put onto what is known as an 'elimination diet', consisting only of meat, fruit and water. Fourteen of them found that their symptoms cleared and wheat was identified as the most common cause of symptoms. Maize and dairy products were next on the list.
Reactions to food chemicals
In addition to chemicals which occur naturally in foods (for example, caffeine in coffee), there are numerous others which may be incorporated - either directly or indirectly - into food during the growing, storage or processing stages. These chemicals include flavouring, colourants and preservatives. The first two are the most common - because of their very wide distribution in foods, beverages and pharmaceutical products, practically everyone has some daily contact with one or more flavouring and colourant. However, the consumer is often surprised to learn that an everday food product contains either a synthetic colour or flavour or both.
In many cases the foods are those especially designed for children, for example sweets and various breakfast foods. Tartrazine is the most common colouring agent used and is found in a wide range of foods, beverages and medicines. The adverse responses to it are similar to those caused by aspirin and can include very severe reactions. Most commonly, it causes urticaria, asthma, nasal discharge and itching. The flavour-enhancer monosodium glutamate (MSG) is usually found in prepared meats, meat extracts and in Chinese food. People who are sensitive to MSG may have a reaction known as the `Chinese Restaurant Syndrome' after eating foods containing the offending compound. Sweating, a feeling of weakness and a tight feeling in the chest are the symptoms.
All this means that people who are sensitive to certain chemicals should be extra careful about reading all food labels carefully and should avoid those foods and drinks which contain possible problem causers. However, it is important to emphasise that naturally occurring chemical substances - such as caffeine in tea, coffee and cola drinks and theobromine in chocolate - may also have adverse effects such as insomnia, restlessness, abdominal pain and nausea in sensitive people. No additives are responsible for these reactions.