Food allergies vs food intolerance

Food allergies and food intolerance are sometimes confused with each other, but they are quite different in terms of their origin, symptoms and treatment. Food allergies trigger the immune system, while food intolerance does not.

Food allergies

True allergic reactions to food involve the body's immune system. When the body identifies a food as harmful, it produces antibodies directed against that food. The next time the food is consumed, the body mounts an immune response with the release of histamine and other chemicals that trigger allergic symptoms. A common example of a food allergy is to peanuts. With a food allergy, symptoms may occur almost immediately or up to a number of hours after consuming the particular food.

Food allergy symptoms can include:

  • Skin rash or hives
  • Swelling of the tongue and throat
  • Breathing problems including asthma
  • Vomiting or diarrhoea
  • Abdominal pain and cramping

Food intolerance

Food intolerance refers to difficulty in digesting certain foods. Foods most commonly associated with food intolerance include dairy products, grains that contain gluten and foods that cause intestinal gas build-up, such as beans and cabbage. The symptoms of food intolerance generally take longer to emerge, compared to food allergies. Onset typically occurs several hours after ingesting the offending food or compound and may persist for several hours or days. In some cases symptoms may take 48 hours to emerge.

Symptoms of food intolerance include:

  • Bloating
  • Migraines
  • Headaches
  • Cough
  • Runny nose
  • Not feeling well
  • Stomach ache

What are the causes of food intolerance?

  • Absence of an enzyme. Enzymes are needed to fully digest foods. If some of these enzymes are missing or insufficient, proper digestion may be undermined. People who are lactose intolerant do not have enough lactase, an enzyme that breaks down milk sugar (lactose) into smaller molecules that the body can break down further and absorb through the intestine.

  • Chemical causes of food intolerance. Certain chemicals in foods and drinks can cause intolerance, including amines in some cheeses, and caffeine in coffee, tea and chocolates. Some people are more susceptible to these chemicals than others.

  • Food poisoning - toxins can cause food intolerance. Some foods have naturally-occurring chemicals that can have a toxic effect on humans, causing diarrhoea, nausea and vomiting. Undercooked beans have aflotoxins that can cause extremely unpleasant digestive problems. Fully cooked beans do not have the toxin. Hence, people may wonder why they react to beans after one meal, and not after another.

  • Natural occurrence of histamine in some foods. Some foods, such as fish that has not been stored properly, can have an accumulation of histamine as they "rot". A number of people are particularly sensitive this naturally-occurring histamine and develop skin rashes, abdominal cramps, diarrhoea, vomiting and nausea. Often, the symptoms are similar to anaphylaxis (a strong allergic reaction).

  • Salicylate intolerance. Salicylates are derivatives of salicylic acid, which occurs naturally in plants as a defence mechanism against harmful bacteria, fungi, insects and diseases. Salicylates are present in most plant-sourced foods, including the majority of fruits and vegetables, spices, herbs, tea and flavour additives. Mint-flavouring, tomato sauce berries, and citrus fruits have particularly high levels of salicylates. Processed foods with flavour additives are usually high in salicylates as well.

  • Food additives are common causes of food intolerance. Food additives are used to enhance flavour, make foods look more appealing, and to increase their shelf life. Examples of food additives include antioxidants, artificial colourings, artificial flavourings, emulsifiers, preservatives and sweeteners. The following food additives are known to cause adverse reactions in people:
    • Nitrates - known to cause itching and skin rashes. Processed meats are generally high in nitrates and nitrites.
    • MSG (monosodium glutamate) - used as a flavour enhancer. Known to cause headaches.
    • Sulphites - used as a food preserver or enhancer. Commonly used in wines.
    • Some colourings - especially carmine (red) and annatto (yellow).

How is food intolerance diagnosed or confirmed?

It is not easy to initially determine whether somebody has a food intolerance or allergy, because the signs and symptoms often overlap. Patients are advised to keep a diary and write down which foods are eaten, what the symptoms were like, and when they appeared. The data in the diary can help a dietician or doctor identify which foods are causing adverse reactions and what steps to take.

Apart from lactose intolerance and celiac disease, there is no accurate, reliable and validated test to identify food intolerance. The best diagnostic tool is an exclusion diet, also known as an elimination or diagnostic diet.

The doctor may recommend a skin test and/or a blood test to rule out a food allergy. This determines the patient's reaction to a specific food. However, skin prick tests are not 100 % reliable. A blood test that measures levels of IgE (immunoglobulin E) antibodies may also be considered. These tests are not 100 % reliable either.

The best current treatment for food intolerance is to either avoid certain foods or eat them less often and in smaller amounts, as well as taking some supplements that may help digestion.

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