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Food intolerances


A food intolerance is a bad reaction to a food, but without involving the immune system.

Symptoms also take much longer to develop and are generally not life-threatening. However, a food intolerance can adversely affect long-term health. Examples include lactose intolerance due to the absence of the enzyme lactase and migraine induced by red wine.

What are the symptoms of an intolerance to a food?

The symptoms of an intolerance to food include those of an upset digestion – diarrhoea, bloating, upset stomach, etc. Weight loss, lethargy or anaemia can occur as well as migraine headaches and psychological effects such as confusion and even depression. However, these usually manifest over longer periods of time as well as a variety of other symptoms that can result from poor nutrition. In some cases the symptoms of a food intolerance resemble those of a mild allergic reaction.

Many of the symptoms of a food intolerance are also associated with other disorders of the digestive system such as Crohn’s disease and Irritable Bowel Syndrome.

What foods can people be intolerant to?

There is also a wide variety of foods associated with food intolerance. The most frequently encountered in an island of Ireland context include milk (lactose intolerance) and gluten (coeliac disease; wheat intolerance) but also certain food additives such as monosodium glutamate (MSG).

  • A person with lactose intolerance cannot digest milk properly (lactose is a milk sugar). Lactose cannot be absorbed by the body resulting in symptoms such as cramps and diarrhoea. For more on lactose intolerance see the medical information section.
  • A person with coeliac disease reacts to gluten which is a protein found in foods such as wheat, rye, barley and oats. This results in damage to the gut with effects on nutritional status and general wellbeing.
  • Some people have reported symptoms such as flushing, temperature increase and headache after eating the flavour enhancer MSG. These symptoms are also known as “Chinese Restaurant Syndrome”, related to the fact that MSG is a frequent ingredient in many Chinese dishes.
  • Other foods to which susceptible people are known to react include red wine, cheese, caffeine and salicylates which are found in certain vegetables, herbs, spices, fruits and chocolate.

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