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Allergy, intolerance: which is it?

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Sharon's body doesn't seem to like wheat much. But at worst, she feels slightly grim when she eats some. Her friend Mandy, on the other hand, ate shellfish, and the next thing she was being wheeled into the ICU. Here's how to tell the difference between food intolerance and food allergy.

Most people have problems with differentiating between food intolerance and food allergy. Surveys conducted by the Food Allergy Centre in the US found that between 14% and 17% of all respondents said that they or a family member suffered from a food allergy.

On the other hand, food allergy studies have shown that only 0.1% to 8% of the population actually have a confirmed food allergy.

Definitions
Food intolerance is defined as "an adverse reaction to a food caused by toxic, pharmacological, metabolic or idiosyncratic reactions to the food or chemical substances in the food". (Krause, 2000)

Food allergy, on the other hand, is defined as "an adverse food reaction that is mediated by an immunoglobulin E (IgE) immunological mechanism; the reaction occurs consistently after consumption of a particular food and causes functional changes in target organs; IgE-mediated food hypersensitivity". (Krause, 2000)

These definitions sound formidable, but what they actually mean is the following: your reaction is classified as a food intolerance if you react once to a food because it contains a toxin, if you react to a food because an additive disagrees with you, or if you react for another reason without your immune system being involved. If, however, you react every time you eat a specific food, it means you have a food allergy.

If you eat shellfish that's contaminated with Salmonella – a food that is, therefore, toxic on a specific occasion – and you get violently ill as a result, this is a food intolerance. It doesn'tt mean that you'll henceforth always react in the same way.

However, if your immune system becomes involved in the reaction to a specific food and every time you eat that food you develop symptoms (which may, incidentally, increase in severity over time), you have a food allergy.

A fashionable condition
One of the most problematic aspects of the intolerance/allergy issue is that it has become fashionable to say that you have a food allergy. I've observed this repeatedly when eating out with friends. At some time or another, the topic of food allergy comes up and at least one or more of the people sitting around the table will state with total conviction that he or she is allergic to X or Y.

The only way to determine if you really have a food allergy is to have tests done by a pathology lab. Your doctor will arrange for you to have such tests carried out if you suspect that you do have a food allergy.

If you're diagnosed with food allergy, you should preferably consult a clinical dietician. He/she will prescribe a diet that will exclude the offending foods, but that will still ensure that you're getting a fully balanced diet.

Don't self-diagnose and don't exclude certain foods because you "think" you have a food allergy. You may actually be allergic to a host of other allergens, such as house dust mites, animal hair or dander, grass seeds, pollen, grasses or rubber, and not have a food allergy at all.

Cutting out certain foods and food groups because of suspected food allergy can lead to deficiencies in vital nutrients. This may have a detrimental effect on your overall health. If you're convinced that you have a food allergy, it's important to go for the tests, get a proper diagnosis and cut out the problem food(s) with the help of a dietician.

Non-immunological food reactions
As mentioned above, food intolerances or non-immunological food reactions, where the immune system is not involved, can also cause a host of reactions varying in severity. However, these are not food allergies. Some of the most common food intolerances include:

  • Lactose intolerance. This is caused by a lack of the enzyme lactase, which is required for the digestion of milk sugar or lactose. It manifests with symptoms of bloating, winds, diarrhoea and abdominal pain. Exclusion of foods that contain lactose and milk is necessary in managing this condition.
  • Inborn errors of metabolism such as phenylketonuria. This is a reaction to all foods containing phenylalanine, which can lead to mental retardation if not identified at an early stage.
  • Reactions to pharmacological compounds such as tyramine. These are found in mature cheeses (Cheddar, Camembert, Brie etc), brewer's yeast, red wine and canned fish. Symptoms may include migraine headaches and skin rashes. It may even precipitate a hypertensive crisis in susceptible patients.
  • Reactions to food additives such as colourants and preservatives. The colourant, tartrazine, can cause hives, skin rashes and asthma. Preservatives like sulfites, that are found in many processed foods, can cause similar symptoms.
  • Reactions to food that's contaminated with microorganisms (see the example above of shellfish contaminated with Salmonella). This can cause acute vomiting and diarrhoea.

It's important to have your doctor assist you in deciding whether you suffer from a true food allergy or if you have a food intolerance, and how this condition should be treated.

For example, peanut allergy is so serious that you need to carefully avoid coming into contact with even minute traces of peanuts. Should you suffer from a peanut allergy, you should preferably carry prophylactic medications with you at all times.

On the other hand, if you have a mild food intolerance, exposure to small quantities of the food may not cause symptoms (e.g. some patients with lactose intolerance are able to have about 200ml of milk a day without adverse reactions), and many reactions only occur once (e.g. poisoning after exposure to a contaminated food).

(Dr I.V. van Heerden, DietDoc, updated April 2009)

References:
(Krause's Food, Nutrition, & Diet Therapy, 10th Edition. LK Mahan & S Escott-Stump Editors, WB Saunders Co, Philadelphia. USA)

Any questions? Ask DietDoc

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