What is Food Intolerance?

The term ‘intolerance’ can be used to describe;
Medical conditions such as ‘lactose intolerance’ – an inability to absorb lactose (found in dairy products), or
Unpleasant reactions to food in the absence of any underlying medical cause.

This article refers to the second kind of intolerance. Food intolerances occur when the chemicals in foods and fluids irritate nerve endings in different parts of the body, in much the same way that drugs can cause side-effects in sensitive people.

What Symptoms can Food Intolerance cause?

Symptoms of food intolerances can vary between individuals and can affect different systems in the body.

Central Nervous System:

  • Unexplained tiredness
  • Dizziness
  • Irritability/Mood Swings
  • Headaches/Migraine
  • Poor Concentration
  • Hyperactivity

Digestive System:

  • Bloating and Wind
  • Indigestion
  • Diarrhoea
  • Constipation
  • Stomach Pain
  • Nausea/Vomiting
  • Mouth Ulcers

Respiratory System:

  • Asthma
  • Runny/Stuffy Nose


  • Hives
  • Swelling
  • Itchiness
  • Rashes

What Foods Commonly cause Intolerance?

People can experience food intolerances to whole foods such as milk and wheat, naturally occurring chemicals such as salicylate, amines and glutamates , or food additives such as artificial colours, flavours and preservatives.

Who is Most Likely to Suffer from Food Intolerance?

People with a history of hives, headaches, irritable bowl or a family history of food intolerances at some stage in their lives are commonly attributed to development of food intolerances. Pregnant women can become more sensitive to food chemicals due to hormonal changes, and as babies, we have immature nervous systems, which make us less tolerant of rich, spicy and highly flavoured foods. Environmental triggers such as severe bout of food poisoning, a nasty viral infection or a sudden change of diet can also alter the way our bodies react to food chemicals.

How is Food Intolerance Identified?

Unlike food allergies, food intolerances do not involve the immune system and therefore cannot be detected through blood tests or Skin Prick Testing. Chemicals present in foods can accumulate in the body and only cause a reason when a person’s ‘chemical threshold’ is reached. Often, we blame the last food that was eaten when in actual fact, it may have been a build-up of a number of different foods over a 1-2 week period.

It’s important to ensure that your symptoms have been assessed by a GP and any necessary diagnostic tests have been undertaken to rule out medical conditions before investigating food intolerance.

The best method of identifying food intolerance is through the ‘Elimination Diet’ (ED), devised by the Royal Prince Alfred Hospital Allergy Unit. The ED diet is completed in two phases:

  • The Elimination Phase, and
  • The Challenge Phase.

The elimination phase is designed to reduce the levels of food chemicals accumulated in the body. This is usually done over a 4-6 week period. If your symptoms do not improve during this period then your problem is probably not related to food intolerance. However, if your problems improve markedly, you will need to proceed to the challenge phases to determine which foods or chemicals are the culprits. An ED and food challenges should only be commenced under the supervision of an APD who specialises in food intolerance.

How do we Treat Food Intolerance?

Although food intolerances can be very unpleasant, they don’t generally cause any permanent damage to the body and the only way to treat them is to avoid the problem foods. How long they have to be avoided for is dependent on how sensitive the individual is. Many people can gradually reintroduce problematic foods into their diets to return to a relatively normal dietary intake. However, people who are highly sensitive may need to limit problem foods for life in order to control symptoms. Your APD will help you establish your threshold and liberalise your diet in accordance with guidelines provided by the Royal Prince Alfred Hospital after the challenge phases has been completed.