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Food intolerance


A food intolerance is a difficulty in digesting certain foods.

For instance, many adults can’t drink milk or eat dairy products because they don’t have the enzyme lactase which breaks down the milk sugar lactose.

What are the symptoms of a food intolerance?

Compared to a food allergy, the symptoms of a food intolerance usually take longer to develop and are generally not life-threatening.

Symptoms can include:

  • abdominal pain and discomfort
  • diarrhoea, bloating 
  • upset stomach

Long-term effects of food intolerances can include:

  • weight loss
  • lethargy or anaemia (due to poor nutrition)
  • migraine headaches
  • confusion
  • depression

Many symptoms of a food intolerance are also associated with other disorders of the digestive system, such as Crohn’s disease and irritable bowel syndrome, or can resemble symptoms of a mild allergic reaction (e.g., itching, skin rash).

What is the difference between a food allergy and a food intolerance?

With a food allergy, your immune system reacts to a food and the symptoms are immediate and can vary from mild to severe or life-threatening. A food intolerance doesn’t involve your immune system and the symptoms, which take a few hours to develop, are never life-threatening. Also, tiny amounts of food can trigger an allergic reaction, whereas you would need to eat a lot of a food to trigger symptoms of a food intolerance.

What foods can people be intolerant to?

Many foods are associated with food intolerance. Some of the more common food intolerances on the island of Ireland are milk (intolerance to lactose), wheat, and certain food additives such as monosodium glutamate (MSG).

How is a food intolerance diagnosed?

Diagnosing a food intolerance can be difficult because the symptoms are common to many other illnesses and diseases.

The most reliable way to diagnose a food intolerance is through a trial elimination diet. This means identifying the food that makes you sick, eliminating this from your diet and seeing if the symptoms go away, then reintroducing the food back into your diet to see if the symptoms return.

If your trial elimination diet requires removing entire food groups or major changes to your diet, then talk to your doctor or a registered dietitian before you start.

While there are many food intolerance tests available, there is no scientific evidence that these tests work, so always talk to your doctor or registered dietitian.

I have been diagnosed with a food intolerance. How can I protect myself?

There is no ‘cure’ for a food intolerance. Once you have been properly diagnosed and the food(s) that make you sick have been identified, you need to take steps to avoid these.

For packaged food, check the ingredients list on the label. When in a restaurant, ordering takeaway or any food sold unpacked, check information on the menu items and talk to staff to make sure that the meal you eat does not contain the food ingredients you need to avoid.

It is easy to remove some ingredients from your diet like MSG. Other intolerances could mean cutting significant sources of nutrients or fibre from your diet – e.g., an intolerance to lactose or gluten. In these cases, talk to a registered dietitian about how you can get these back into your diet from other sources.


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