How is a Food Allergy Different to Food Intolerance?

Food allergy is an immune system reaction to a food, while food intolerance is a digestive issue.

A food allergy is an immune system reaction to a food, that can cause life-threatening symptoms like swelling and anaphylaxis.  A food intolerance is a digestive issue that causes discomfort, but it is not life-threatening.

Symptoms of an allergy can appear within minutes of eating a small amount of the food, whereas intolerance symptoms are typically delayed and often depend on the amount consumed.

Food intolerance

Food intolerance refers to an individual’s ability to handle different types of food or drink.  Food intolerance is not a true allergy.  There is no clearly defined immune response and the symptoms that often develop only affect the digestive tract.

An intolerance is normally found in the context of a deficiency in certain enzymes that break down the components of food.  The absence of these enzymes results in abnormal by-products that produce the symptoms of intolerance.

Food intolerance means the individual can eat small amounts of food without obvious consequences while eating larger amounts or more regular consuming of the food may lead to stomach cramps, nausea, or diarrhoea.

Food allergy

In contrast, a true food allergy tends to affect multiple organ systems within the body and tends to have a poorer outcome.  The reaction, can involve the skin, respiratory system, heart or gastrointestinal tract.

A true food allergy means that the individual is required to avoid that food for life or risk the consequences.  Even a tiny amount of the allergy-causing food can trigger symptoms.

Food allergy vs food intolerance

A good example of the difference between a food allergy and food intolerance is comparing coeliac disease, an allergy, with lactose intolerance.

Patients with coeliac disease have an allergy to gluten.  In coeliac disease, the ingestion of gluten results in a specific immune response against the gluten, leading to inflammation and the destruction of the lining of the small intestine.  This leads to the malabsorption of important vitamins and minerals, which if left untreated can be life-threatening.

Lactose intolerance is due to a deficiency in the enzyme (lactase) that breaks down lactose.  The absence of this enzyme results in abnormal levels of lactose in the bowel, that leads to the feeling of bloating, diarrhoea, cramps, and nausea.  While uncomfortable, the continued ingestion of lactose is not life-threatening.