What is a food intolerance?

A food intolerance is when certain foods you eat cause you to have an upset stomach or other symptoms that make you feel unwell. Food intolerances are not food allergies.

What is the difference between food intolerances and food allergies?

If you have a food allergy, your immune system mistakes a protein found in a food as dangerous. Your immune system reacts within minutes or hours after eating that food. Your symptoms can range from a mild rash to life-threatening anaphylactic shock. Even tiny amounts of food can cause an anaphylactic shock if you're allergic.

Food intolerances do not involve your immune system. You develop a food intolerance when your digestive system cannot break down or absorb a certain food. Your symptoms are not life-threatening but the more of the food you eat, the worse you will feel.

What are the most common types of food intolerance?

The most common food intolerances are:

• lactose intolerance — lactose is a sugar found in dairy products.
• gluten intolerance — gluten is a protein found in wheat, rye and barley.
• fructose intolerance — fructose is a sugar found in fruit, honey and some vegetables
• food chemical intolerances — these may be in natural or processed foods
• FODMAP (fermentable oligosaccharide, disaccharide, monosaccharide and polyols) intolerances — a group of sugars found in some fruits and vegetables, cereals, dairy products and sweeteners.

Lactose and fructose intolerances can also be part of FODMAP intolerance, but they are listed separately because they are more common. You can also have a lactose or fructose intolerance without having other intolerances.

Food chemical intolerances

Food chemical intolerances include sensitivities to:

• sulfites — food additives in dried fruits, grape juice, lemon and lime juice, cider and wine
• histamines — natural chemicals in pineapple, banana, citrus fruits, avocado, baked meat, red wine, chocolate and mature cheese
• glutamates, including MSG (monosodium glutamate) — found in food additives —, Camembert and Parmesan cheese, tomatoes, mushrooms, soy sauce, some stock cubes and yeast extract

Food chemical intolerances are less common than other intolerances.

What are the symptoms of a food intolerance?

If you have a food intolerance, you may experience some of these stomach symptoms, hours or days after eating the food you are intolerant to:

• bloating
• stomach pains
• diarrhoea
• nausea
• flatulence
• constipation

Lactose and gluten intolerance can cause other symptoms, including:

• fatigue
• headaches
• depression

Food chemical intolerances can also cause:

• migraines and dizziness
• itchy skin, eczema and hives
• blocked nose or runny nose, asthma symptoms and sneezing
• fast heartbeat

Your symptoms can range from mild to severe.

What causes food intolerance?

Food intolerances develop when your body cannot properly break down or absorb a food. For example, lactose and histamine intolerances happen when your body does not have the right type or amount of enzymes (special proteins) to digest food properly.

Some conditions or medicines can increase your risk of having a food intolerance, sometimes for a short time only, such as:

• gastroenteritis
• Coeliac disease, inflammatory bowel disease (IBD)
• AIDS (acquired immunodeficiency syndrome)
• malnutrition
• chemotherapy
• antibiotics and other medicines

When should I see my doctor?

You should see your doctor if you:

• think you have a food intolerance
• have a diagnosed food intolerance and need advice or a referral to a dietitian
• are being treated for a food intolerance and your symptoms are not improving

How is a food intolerance diagnosed?

Your doctor can diagnose a food intolerance by:

• asking about your symptoms and medical history
• recommending you follow an exclusion diet and then gradually reintroduce foods
• ordering medical tests, such as skin prick tests and blood tests, to rule out allergies or other conditions

Food intolerances can be hard to diagnose because there are no specific diagnostic tests. Your symptoms might also be very general or caused by many different conditions.

Breath tests and biopsies for lactose and fructose intolerances are not recommended. They can give inaccurate results. This may make you exclude foods from your diet when you don't need to.

There are lots of advertised tests on the market that claim to diagnose food intolerances — many of them don't have enough proof or research to know if they are reliable. Before you see a healthcare professional, check their credentials and if they are registered.

Exclusion diets

Your doctor or dietitian will ask you to remove certain foods from your diet. The aim is to find out which foods trigger your symptoms. You will then gradually reintroduce foods one by one into your diet.

If your symptoms do not improve, it is likely that something else is causing them. Your doctor may then investigate other causes.

Exclusion diets in children should be managed by a paediatric gastroenterologist (specialist doctor).

Your doctor or dietitian will guide you through your exclusion diet. They will explain which foods you can and cannot eat. They will also suggest alternative foods and help you make sure your exclusion diet is healthy.

How is a food intolerance treated?

If you have a food intolerance, your treatment includes cutting down the foods causing symptoms, so you only eat as much as you can without feeling sick. You may not need to completely cut out foods you are intolerant to.

Examples of these diets are low-lactose diets, low-histamine diets, low-FODMAP diets and gluten-free diets.

You will be treated by a registered dietitian. Your dietitian can:

• teach you about food intolerances and how they affect your body
• explain which foods have ingredients you are intolerant to
• teach you to read food labels so you know what you can safely eat
• suggest alternative options to foods you need to exclude or reduce in your diet

Treatment of lactose intolerance

If you have lactose intolerance, as well as a low-lactose diet, your treatment may include:

• lactase enzyme drops or pills — these replace the enzymes you lack and help you digest lactose. Take before you eat foods with lactose.
• probiotics — healthy gut bacteria
• prebiotics — foods that help good gut bacteria grow

Living with a food intolerance

Living with a food intolerance can be challenging. It is not easy to always check food labels and ingredient lists. Some diets are harder and more restricting than others.

Here are some tips to help you manage:

• Download helpful apps, such as the Monash University FODMAP Diet app.
• Join online or support groups for emotional and practical support.
• Plan ahead. If you are eating out, let your host or chef know in advance that you have special dietary needs.
• Cook at home when you can. This way, you have full control of your food. This can reduce anxiety.
• Talk with your dietitian. They can help you avoid restricting foods you do not need to, and have a balanced diet.

What are the complications of a food intolerance?

Some food intolerances and their treatments can cause complications, including:

• nutrient deficiencies — avoiding dairy foods can reduce your intake of calcium and other vitamins and minerals. This can increase your risk of developing bone diseases, including osteopenia and osteoporosis.
• mental health and quality of life challenges — your symptoms may trigger anxiety and depression. Some restrictive diets, for example low-FODMAP diets, have been associated with developing some eating disorders. Talk to your doctor or dietitian if this affects you.

Can a food intolerance be prevented?

Unfortunately, you cannot prevent a food intolerance. They can develop at any age, even if you have previously eaten the food without any problems.

Resources and support

• Learn more about the difference between food allergies and food intolerances on Allergy & Anaphylaxis Australia.
• Nutrition Australia has a resource with helpful information about food intolerances.
• Visit Dietitians Australia for diet and nutrition health advice about lactose intolerance.

You can call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available 24 hours a day, 7 days a week.