Food allergies
Many people notice symptoms after eating a certain food and convince themselves that an allergy is the cause. Here's why you shouldn't self-diagnose.
What is an allergy?
A true food allergy is an immune reaction to an allergen (a foreign substance). Common allergens in children are: cow's milk, egg, wheat, soya, and nuts. In adults: seafood, nuts, or certain fruit and vegetables can also cause reactions. Up to 20% of people claim to have some kind of food allergy, but only around 1% of adults and 3-4% of children are truly allergic, according to a report by the British Medical Journal.
Common symptoms
- Rashes, itching, breathing difficulties and swollen lips or mouth.
- Vomiting, stomach cramps, and diarrhoea.
- In extreme situations the person may collapse in anaphylactic shock, which needs immediate treatment with an injection of adrenaline.
- In coeliac disease there is a delayed immune response to wheat protein, causing damage to the lining of the intestines and diarrhoea.
I think I may have an allergy
The best way to tell is to get a diagnosis by a doctor. This will involve them taking a full history of the symptoms, and usually a skin prick test or RAST (Radio Allergo Sorbent Test) test. Skin prick tests are relatively simple: a fine needle is used to gently prick through a drop of liquid that contains a known allergen. Several of these tests can be done on the forearm, and an allergy will cause reddened, itchy weals where the needle went in. For the RAST test, a blood sample is taken and tested for specific antibodies (IgE) that act against certain foods. This method can be used to test for over 400 allergens.
There are many other tests available, but some of them are unscientific and are considered to be inaccurate by bodies such as the British Society for Allergy and Clinical Immunology, or the British Medical Journal. Misdiagnosis of allergies can lead to a person severely restricting their diet, and even reaching a state of malnutrition. Some of these discredited tests include:
- Leucocytotoxic tests: white blood cells are mixed with allergens.
Vega testing: 'disordered electromagnetic currents' in the body are tested for. - Applied kinesiology: loss of muscle strength is tested for.
- In addition to the skin-prick or RAST tests, the person may be asked to keep a food diary to see when their symptoms occur. They may also be asked to do a 'double-blind test' where they are fed two meals on separate occasions that appear identical, but one of them contains the substance they are supposedly allergic to.
Sometimes it is appropriate to follow an exclusion, or elimination, diet for between two and four weeks. The person eats only foods they know they're not allergic to for a few days, then starts reintroducing foods that are possible suspects. This must only be done for short periods, preferably under supervision of a dietician to make sure nutritional deficiencies do not occur.
Coping with food allergies
If you are certain that you have an allergy, be sure to avoid that food by checking packets and labels of anything you eat, and being extra-careful when eating out in restaurants. If an itchy reaction has already started, antihistamines may help, but discuss this with your doctor. If there is a risk of anaphylactic shock (circulatory collapse), an adrenaline injection can be carried by the sufferer, who should also tell friends how to inject them if an emergency arises.
What's the difference between an allergy and intolerance?
Intolerances - or food sensitivities - are more common than allergies and do not cause the same immune response. With an allergy, a tiny amount of the problem food can cause a reaction, whereas an intolerance usually requires a larger quantity to be consumed for a reaction to take place. Often the symptoms of food intolerance start some time after eating the food, which can make the condition difficult to diagnose.
Common symptoms include: flushing, abdominal pain, vomiting, and diarrhoea.
What causes intolerance?
- In lactose (milk) intolerance, sufferers lack the enzyme to digest the milk sugar. In some countries such as Thailand, more than two thirds of the population are lactose intolerant, although it is much less common in the UK.
- In gluten intolerance (also known as coeliac disease), the gluten causes the immune system to produce antibodies that can damage the lining of the small intestine.
- Yeast intolerance, or candida, is caused by the overproduction of yeast in the body. Sugar-rich food, antibiotics, steroids and contraceptive hormones can all boost yeast levels.
- Reactions to certain food additives, such as sulphites, monosodium glutamate, and caffeine.
- Certain people are sensitive to the effects of a chemical called histamine, found naturally in some foods.
Detecting intolerances
If you suspect that you have a food intolerance you should visit your GP before cutting out any food groups entirely, which could resultin your diet falling short of vital nutrients. Only after you have been properly diagnosed should you avoid the problem food - preferably under the consultation of a GP or nutritionist.
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