Food intolerances

Food intolerance covers all other food-related reactions, generally those that cannot be tested for. Food intolerance can affect anyone at any age and usually involves more than one food. Reactions can be delayed for several days and the reaction is usually dependent on the amount of food eaten. Symptoms of food intolerance include:

  • Skin: hives, swelling, eczema
  • Respiratory: asthma, sinusitis, nasal congestion
  • Gastrointestinal: nausea, vomiting, diarrhoea, constipation, gas, abdominal pain
  • Other: migraine, nerve pain, muscle pain, impairment of memory, depression.

The types of food intolerance

Food intolerance can be divided into several groups.

Enzyme deficiency

If an enzyme in your digestive system is missing or not functioning correctly, it won't be able to help digest the food it is associated with. This will cause digestive-related symptoms such as diarrhoea, bloating, wind and abdominal pain.

The most common enzyme deficiency is lactase, which causes lactose intolerance. Lactase digests the milk sugar lactose. Usually people can still tolerate small amounts of lactose-containing foods.

Other enzyme deficiencies are rare, but fructose, maltose and sucrose intolerances do sometimes occur. See your GP or dietician if you suspect lactose intolerance.

Allergy-like intolerances

There are some reactions to foods that commonly cause allergy, such as milk, wheat, egg and soy etc that are actually intolerances. These will not appear on allergy tests but can be tested for using atopy patch tests. This involves applying a paste of the suspected food to a patch of skin on your back and then monitoring for reactions over hours. These tests are only done by a specialist. Intolerances to foods are most easily diagnosed by an elimination diet under the supervision of a dietician.


Some foods can be irritating to the digestive system, causing symptoms such as diarrhoea, wind, abdominal pain and bloating. Examples of irritants are caffeine, spices, garlic, onions, cabbage, dried fruit and sorbitol (found in sugar-free foods such as chewing gum).

Food chemical intolerance

The two main classes of chemicals that occur naturally in foods are salicylates and amines. These can affect or cause asthma, pruritis, hives, eczema and migraines.

Food toxins

Some foods contain natural toxins that can increase under certain conditions. Other foods produce toxins as they spoil. Some people may be very sensitive to these toxins and so be more likely to experience adverse effects.

  • Spoiled fish produces histamine which can produce allergy-like reactions.
  • Green sprouting potatoes may cause stomach ache.
  • Kumara and parsnip damaged by insect attack or injury may cause illness. Cut out the damaged area and peel before cooking. Don't eat it if it tastes bitter.
  • Dried beans and chickpeas contain toxins. These need to be soaked and cooked thoroughly to remove them.
  • Zucchini that tastes bitter or has a strong unpleasant smell may contain toxins from wild zucchini strains and should not be eaten.
  • Cassava, taro leaves and bamboo shoots must be properly prepared and cooked before eating.


Sulphites in food are required to be listed on food labels, although sulphite reactions are not due to an allergy, but intolerance.

Sulphites are preservatives used most commonly in wine and dried fruit. The additive numbers are 220 – 228. Sulphites will appear as one of these numbers in ingredients lists on food labels. Above a certain level, labels will say "contains added sulphites".

Sulphites mainly cause asthma in sensitive people, but may also cause rashes, irritable bowel syndrome and headaches.