What’s the difference between a food intolerance and food allergy?

Symptoms of food intolerance and food allergy may be similar, but it is important to understand the differences between the two. Eating a food you are intolerant to can make you feel miserable. However, if you have a true food allergy, your body’s immune response to this food can be life-threatening.

Food allergy vs food intolerance

A food allergy reaction occurs when your immune system reacts aversely to a food or a substance in a food, identifying it as a danger and triggering an allergic response.

In contrast, a food intolerance occurs when the body has difficulty digesting certain food components, leading to symptoms of pain and/or discomfort.

This was shared by Ong Jiaxin, Dietitian, from the Nutrition and Dietetics Department, and the Allergy Service, both departments from KK Women’s and Children’s Hospital (KKH), a member of the SingHealth group.  

The table below shows the main differences between food allergies and food intolerances:

​ ​Food Intolerance ​Food Allergy
​Involvelment of body systems ​Does not involve the immune system ​Involves the immune system
Symptoms ​Mainly gut symptoms and rarely life-threatening ​Symptoms vary in severity. In severe cases, the airway, breathing and circulatory systems may be involved. Such severe reactions are called anaphylaxis
​Onset of symptoms ​Usually slower to develop ​Immediate to delayed to develop
​Amount of food tolerated ​Symptoms often dose-dependent, usually requires large amounts of offending food, so small amounts may be tolerated

 

​Eating, touching or inhaling a tiny amount of the food (uncommon) can elicit an allergic reaction 

 

​Diagnosis ​Difficult to diagnose as there are no validated tests to diagnose food intolerances. May be identified through food elimination and reintroduction ​Diagnosed using:
  • Skin prick test (SPT)
  • Immunoglobin E (IgE) blood test
  • Oral food challenge  
​Examples
  • ​Lactose intolerance
  • Irritable bowel syndrome
  • Intolerance to food additives/chemicals
  • ​Cow's milk
  • Hen's egg
  • Soy
  • Peanut
  • Tree nut
  • Wheat
  • Shellfish allergy
  • Galacto-oligosaccharide (GOS) allergy

Types of food allergies that involve the immune system

IgE-mediated allergy: Reactions usually immediate or develops within minutes to 1-2 hours after eating the offending food

Non-IgE mediated allergy: Reaction usually delayed, presents several hours to up to two days after the ingestion of food. If the offending food continues to be eaten in the diet, the immune system will continue to produce the symptoms over days or even weeks.

The focus of this article is on IgE-mediated food allergy. Symptoms of this type of food allergy can range from mild to severe. Just because an initial reaction causes few problems doesn’t mean that all reactions will be similar; a food that triggered only mild symptoms on one occasion may cause more severe symptoms at another time.

While any food can cause an allergic reaction, eight types of food account for about 90 percent of all reactions:

  • Peanuts
  • Tree nuts (e.g. almond, cashew, macadamia, pecan, pistachio, walnut)
  • Eggs
  • Milk
  • Wheat
  • Fish
  • Shellfish (e.g. clam, lobster, prawn, oyster, scallop)
  • Soy

Read on for symptoms of food allergies.

Ref: M19