Difference between Food Allergy and Food Intolerance

Both a food allergy and intolerance can make your body sensitive to a particular food or ingredient causing unwanted physical reactions whenever you eat the foodie culprit.

Only 2% of the adult population have a food allergy, where as 45% have a type of food intolerance.

Food allergy occurs when an antigen or trigger in the food reacts with specific immunoglobulin (also known as antibodies) in the immune system, as your body recognises the food as a foreign substance (allergen) when eating the food for the first time.

When you eat the offending food again, the antibodies attack the allergen, producing histamine and other chemical, setting off various types of symptoms.

Some foods are also naturally high in histamines. These include aged and fermented foods and alcohol (especially red wine), some people are sensitive to these types of foods.

‘Histamine poisoning’ can happen if you eat fish not kept at safe temperatures and has spoiled before you ate them. Those fish can build up high levels of histamines, which can make you sick.

Anaphylaxis is the most dangerous kind of an allergic reaction, involving the breathing and circulation, and causing faintness and shock, with a fall in blood pressure and in serious cases can lead to death (nut allergy, for example). Symptoms of food sensitivity include swelling of the lips, diarrhoea and vomiting. You may have eczema, a very runny nose or asthma.

Usually the reaction is acute and immediate, but it may be delayed, as in the case of coeliac disease (gluten being the allergen).

A food allergy can be tested by a patch test or blood test from your local doctors.

Food intolerance reactions are not caused by the immune system but is brought about by other mechanisms. For example, a milk intolerance (lactose intolerant) is due to a lack of a particular digestive enzyme, lactase.

Some active chemicals may be present in the food causing a reaction, such as caffeine, causing a racing heart and tremor. Some suffer from food additives provoked by hypersensitivity.

The timing of these symptoms vary, swelling tissues, vomiting and a runny nose appear within one hour. Rashes and diarrhoea may take longer, 2-24hours. Some disorders, headaches and irritability, may last for several days.

Long term problems relating to food include irritable bowel, hyperactivity disorder and migraine.

A food intolerance causes different reactions for different people so there is no definite test to find out your food intolerance. Monitor what you are eating and how it makes your body react and always seek professional advice from your local doctor.

In some cases, weeks or months of elimination of the intolerant food may well lead to reintroduction of the food without a reaction, as your body learns to build up a tolerance.


For further reading please see here there is a wealth of free food fact sheets on the Association of UK Dieticians website, all very useful and available here.

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