Fast facts on food intolerance

Originally posted on

Nov 22, 2013

Food intolerance is a broad label that describes adverse reactions to food that do not involve the immune system. This site uses the term food intolerance as it has been defined by the Allergy Unit at the Royal Prince Albert Hospital in Australia, which corresponds to what some call pharmacological food intolerance.

What is food intolerance?

Food intolerance occurs when chemicals in food produce side effects, similar to the way that drugs produce side effects. Some people are more sensitive to these effects than others.
Food intolerance is not an allergy. A food allergy is an oversensitivity to a protein in a specific food, while food intolerance is a sensitivity to chemicals found in a wide variety of foods.
Organic, fresh, or processed foods can all cause adverse reactions – not all trigger chemicals are man-made.
Symptoms can be physical or behavioral, especially in children. Some people suffer from more than one symptom, and symptoms can change over time.

More information: The food intolerance primer

Who gets food intolerance?

Food intolerance may affect up to 10% of the population when all food chemicals are considered, which is at least 2 times the prevalence of food allergy. Still, this means that food intolerance is relatively rare: for each food chemical, perhaps 99% of the population will experience no adverse effects.
Food intolerance is more common in adults than in children. Lifestyle factors may play a part in this. In comparison, more children suffer from food allergies than adults.
Children with food intolerance are more likely to be sensitive to food additives (artificial colors, flavors, and preservatives) than adults.
Food intolerance seems to run in families, although each family member may be sensitive to a different food chemical. More women experience food intolerance than men.
Food intolerant people are also likely to suffer from allergies. Food intolerance can make existing flare-ups of eczema and asthma worse, but cannot bring about these conditions on its own.

More information: The prevalence of food intolerance

When do people experience food intolerance symptoms?

Symptoms can take hours to days to appear.
The severity of symptoms depends on how much of a food chemical was eaten, even over the course of several days.
Since symptoms are dose-dependent, they may seem unpredictable – sometimes they happen, sometimes they don’t. But if you think of food in terms of its chemical constituents, it all starts to make sense.
Some people are sensitive to more than one chemical and need to eat them in combination in order to see symptoms. Others only experience symptoms when they are under stress, sick, or have been exposed to chemicals in their environment.

More information: Unpredictable symptoms? It’s not always the last thing that you ate

How do I know if I have food intolerance?

Food intolerance should be considered only after your doctor has ruled out food allergies and other conditions and has given you the go ahead.
An elimination diet followed by food challenges is the only way to diagnose food intolerance.
Foods can contain more than one trigger chemical, making the order of the food challenges very important for ruling out all possible triggers. A registered dietitian can help.

More information: Diagnosing food intolerance