What is a food intolerance and how is it diagnosed?

Unlike food allergies, which can trigger severe and immediate reactions, food intolerances often manifest subtly, making them tricky to identify. In this guide, we’ll delve into what food intolerances are, how they differ from food allergies, and how they are diagnosed.

What is a food intolerance?

A food intolerance occurs when you are sensitive to a certain food or ingredients in food. When you eat these foods, you may get symptoms such as nausea, bowel changes, an itchy mouth, or a rash.

We do not know the cause of food intolerances but it is thought there could be a genetic component. Other influences such as your medical history, environment, sudden dietary changes, or a viral infection (e.g. gastroenteritis) can result in a food intolerance.

While some people may experience mild symptoms, for others it can cause great distress when it comes to eating. Understanding what a food intolerance is and how it can be diagnosed is important if you suspect food is the culprit behind your uncomfortable symptoms.

Types of food intolerances

There are different types of food intolerances and some common examples include the following.

Food chemicals

Food chemicals are naturally found in plant and animal foods to varying amounts. Some people are sensitive to food chemicals such as salicylates, amines, and glutamate.

Food additives

These are added to food as preservatives, colours, and flavours. They are chemically similar to food chemicals and can cause symptoms in sensitive people.

Lactose

Lactose intolerance is a common intolerance caused by a lack of lactase enzyme in the digetsive tract. It can result in wind, loose bowel motions, and cramps. You can learn more about lactose intolerance and how to manage it here.

FODMAPs

These are short chain carbohydrates found in many plant foods. They can be a trigger of symptoms in people with IBS and completing a FODMAP diet protocol with a dietitian is the best way to understand which FODMAPs you are sensitive to.

Wheat and soy

Some people are sensitive to wheat or soy and consuming foods rich in these ingredients can trigger symptoms.

How are food intolerances different to food allergies?

Food intolerances are not the same as food allergies. Food allergies involve your immune system and can lead to severe reactions like anaphylaxis when even a small amount of the food is consumed. Food allergies can be diagnosed using a skin prick test or a blood test (known as RAST panel).

To manage an allergy, the food must be completely excluded from a person’s diet as even a small amount of the food can cause an allergic reaction.

On the other hand, food intolerances do not involve the immune system. Symptoms occur from difficulty digesting a food component or due to sensitive nerve endings. People with food intolerances are thought to have more sensitive nerves and certain foods may irritate these nerves and cause a reaction.

Another difference is that people with food intolerances do not need to completely exclude the guilty food from their diet. This is because you can consume an amount of food before you experience symptoms. This is known as the threshold and it is individual to each person. Working with a dietitian can help you to determine your threshold.

What are the symptoms of a food intolerance?

Because food intolerances are the result of sensitive nerves or digestive system, symptoms can affect your entire body. Every person’s symptoms will be unique to them and you cannot diagnose a food intolerance from symptoms alone.

Common symptoms include:

1. Skin reactions: hives, swelling, and eczema.

2. Nervous system: headache, irritability, and fatigue.

3. Respiratory: sinus congestion, throat irritation, and asthma.

4. Gastrointestinal: reflux, nausea, diarrhoea, constipation, bloating, wind, and mouth ulcers.

If you have any of these symptoms, it does not necessarily mean you have a food intolerance. These could be symptoms of another illness or condition and should be investigated with your medical team BEFORE you make any dietary changes.

How are food intolerances diagnosed?

Unlike food allergies, there is no test you can do to diagnose a food intolerance. The only way to understand which food you are sensitive is to complete an elimination diet with staged reintroductions.

The elimination diet is a short diet (generally 2-6 weeks) where you cut out the suspected foods. Your symptoms are assessed during this period to see if there is any improvement. Working with a dietitian ensures you are completing the elimination phase correctly and that you continue to have a balanced diet during this period.

The next phase is the staged reintroductions. This is where a food is brought back into your diet and your symptoms are monitored. It helps to pinpoint which foods or ingredients you are sensitive to and how much you can tolerate (your threshold). This allows you to make informed choices about your diet moving forward.

Before you start cutting out food from your diet it is important to speak with your doctor and dietitian to see if an elimination diet is right for you. Your doctor will investigate your symptoms and rule out other causes. A dietitian will review your diet and symptoms and help guide you through appropriate dietary changes.

Elimination diets and eating disorders

If you have a history of an eating disorder or disordered eating, strict elimination diets may not be suitable for you. This is because elimination diets have many rules and restrictions that can easily feed into disordered eating practices.

This does not mean you must suffer with your food intolerance. It simply means you will need to take a different approach that is less restrictive. Working with a dietitian who specialises in both disordered eating and food intolerances (such as myself) can help you find the best approach.

Getting support

If you want support managing uncomfortable gut symptoms or improving your nutrition, Kim is a dietitian who provides nutrition counselling through a virtual clinic. Kim takes an approach that is personalised to each individual and seeks to understand what you need to reach your health goals.

Kim is a Credentialed Eating Disorder Clinician and has a special interest in digestive health and recovery from eating disorders and chronic dieting. Find out more here.

About

Kim Lindsay, APD

Kim Lindsay is an accredited practicing dietitian and credentialed eating disorder clinician.

She provides online dietitian appointments for people who want to improve their health while developing a positive relationship with food. Kim has a special interest in disordered eating, chronic dieting, and digestive health.

What is a food intolerance and how is it diagnosed?

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