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Knowledge Base » Food Hygiene » What is a Food Intolerance?

What is a Food Intolerance?

Food intolerance and sensitivity are common and they appear to be on the rise. It is estimated that up to 20% of the world’s population may have a food intolerance. The symptoms of a food intolerance vary widely, therefore making it difficult to accurately measure how many people are affected in the UK.

What is a food intolerance?

When you have a food intolerance or food sensitivity, it means that your digestive system finds it difficult to digest that particular food. It means that your gut is sensitive to certain foods and cannot tolerate them. Having a food intolerance is different to having a food allergy.

A food allergy affects the immune system. It occurs when your immune system mistakes a protein or another ingredient in the food for a threat. Your immune system then releases antibodies in order to fight the perceived threat.

A food allergy causes an allergic reaction which can include:

  • Shortness of breath.
  • Hives and swelling.
  • Skin irritation.
  • Wheezing.
  • A severe, life-threatening allergic reaction called anaphylaxis.

An allergic reaction will occur within a few minutes of eating the food that you are allergic to.

A food intolerance affects your digestive system and causes symptoms which are not life-threatening. Symptoms may begin within a few hours of eating the particular food. A food intolerance does not trigger the immune system like an allergic reaction does and the symptoms are usually less severe. Having a food intolerance can negatively affect your health and it should be taken seriously and should be treated.

Skin reaction due to food intolerance

What causes a food intolerance?

A food intolerance is caused by your body being unable to digest a particular food or ingredient in the food. It may be due to a lack of enzymes or a sensitivity to certain chemicals. Food intolerances are more common in people who have digestive system disorders, for example, irritable bowel syndrome.

Most people who have irritable bowel syndrome will have a food intolerance. It is not fully understood why some people are intolerant to certain foods; however, having an existing gastrointestinal condition appears to be a risk factor. A food intolerance can be hereditary, you can have it in childhood or it can develop later in life.

What are the signs of symptoms of food intolerance?

If you have a food intolerance, you will often experience discomfort after eating that particular food.

Common symptoms of a food intolerance include:

  • Stomach pain.
  • Bloating.
  • Excessive wind.
  • Migraine.
  • Headaches.
  • Diarrhoea.
  • Sickness.
  • Nausea.
  • A runny nose.
  • Skin rashes.
  • Flushing of the skin.
  • Generally feeling unwell.

The amount you eat of the food you are intolerant to will determine the severity of your symptoms. The symptoms may begin several hours after eating the food to which you are intolerant and may last for several hours or days. It can therefore be difficult for some people to pinpoint exactly what is causing their symptoms.

What are the different types of food intolerance?

Foods which are commonly associated with food intolerance include:

Milk and dairy

Lactose is a sugar which is found in milk and dairy products. It is broken down in the body by an enzyme called lactase. Without this, lactose cannot be properly digested or absorbed resulting in digestive symptoms. Lactose intolerance is very common, and it is estimated that 65% of the world’s population has difficulty digesting lactose.

The symptoms of lactose intolerance include:

  • Bloating.
  • Abdominal pain.
  • Diarrhoea.
  • Nausea.
  • Wind.

If you think you have an intolerance to lactose, you should avoid dairy products that contain lactose such as milk and ice-cream.

Food intolerance to milk and dairy


Gluten is the name given to proteins found in wheat, barley, rye and triticale.

Foods that contain gluten are:

  • Bread.
  • Cereals.
  • Pasta.
  • Crackers.
  • Baked goods.
  • Beer.
  • Some sauces.

There are several conditions which are related to gluten intolerance; these include coeliac disease, wheat allergy and non-coeliac gluten sensitivity. When people with coeliac disease eat food containing gluten, their immune system attacks their small intestine. This can lead to their digestive system being seriously harmed.

Wheat allergies produce an antibody which causes an allergic reaction and the symptoms will usually be similar to that of coeliac disease. Many people who test negative for coeliac disease or a wheat allergy can still have a gluten intolerance and experience similar unpleasant symptoms. This is a milder type of gluten intolerance known as non-coeliac gluten sensitivity and is estimated to impact up to 13% of the population.

Symptoms can include:

  • Bloating.
  • Diarrhoea.
  • Constipation.
  • Stomach pain.
  • Headaches.
  • Fatigue.
  • Skin rash.

Coeliac disease and non-coeliac gluten sensitivity can be managed with a non-gluten diet. This involves cutting out all foods that contain gluten.

Gluten in pasta can be a food intolerance


Fructose is a sugar found in fruit and vegetables and sweeteners, for example, honey. People are consuming more and more fructose and it has been linked to obesity, heart disease and liver disease. There has also been a rise in fructose intolerance.

This means that fructose isn’t efficiently absorbed into the blood, therefore meaning it has to be processed by the large intestine which can cause digestive issues. High fructose foods should be avoided.

These include:

  • Honey.
  • Apples.
  • Apple juice.
  • Apple cider.
  • Fizzy drinks.
  • Watermelon.
  • Cherries.
  • Pears.
  • Sugar snap peas.
  • Agave nectar.
  • Foods containing high-fructose corn syrup.

Symptoms of fructose intolerance include:

  • Sickness.
  • Nausea.
  • Diarrhoea.
  • Abdominal pain.
  • Bloating.
  • Painful wind.
Fizzy drinks with fructose in


Salicylates are natural chemicals which are produced by plants. Their purpose is to defend against insects, disease and other environmental stressors. These natural chemicals are found in foods like fruits, vegetables, nuts, spices, honey and tea and coffee.

Salicylates are also used as a preservative in some foods and medications. Some people are extremely sensitive to salicylates and can have symptoms after consuming only small amounts. Removing salicylates from your diet completely is not possible; however, if you have an intolerance to salicylates then you should not eat foods which are high in them.

These include oranges, raisins, coffee and some spices. You should also avoid medication and cosmetics which include salicylates.

Symptoms of salicylates sensitivity can include:

  • Sinus infections.
  • A blocked nose.
  • Diarrhoea.
  • Stomach issues.
  • Asthma.
  • Hives.
Stomach issues due to food intolerance


Caffeine is a chemical which is found in beverages including tea, coffee, some fizzy drinks and energy drinks. Caffeine is a stimulant, meaning it increases alertness and reduces fatigue. Most adults can safely consume up to 400mg of caffeine per day without having any side effects; however, some people are more sensitive and have side effects after drinking only small amounts of caffeine.

A sensitivity to caffeine is different to an allergy to caffeine as an allergy affects the immune system. It is thought that a caffeine sensitivity is linked to genetics and a decreased ability to digest caffeine.

Symptoms of a caffeine sensitivity may include:

  • Insomnia.
  • Anxiety.
  • Restlessness.
  • Shaking.
  • Increased heart rate.


Histamine is the amine which is most frequently associated with food intolerance. It is a chemical found inside the body and helps the digestive, immune and nervous systems to function.

It produces an inflammatory response to allergens, which may make you sneeze, feel itchy or have watery eyes. This helps protect the body from infection. People who have a histamine intolerance have difficulty breaking down histamine which can cause a variety of symptoms.

Symptoms can include:

  • Hives.
  • Itchy skin.
  • Flushing/redness of the skin.
  • Headaches.
  • Anxiety.
  • Stomach pain.
  • Diarrhoea.
  • Low blood pressure.

Amines are produced by bacteria during the food storage and fermentation process. They are found in a wide variety of foods. People who are intolerant to histamine should avoid foods that are high in it.

These include:

  • Dried fruits.
  • Citrus fruits.
  • Fermented foods.
  • Cured meats.
  • Avocados.
  • Vinegar.
  • Smoked fish.
  • Aged cheeses.
  • Fermented alcohol.
  • Buttermilk and other soured foods.
Avocado have amines


Sulphites are chemicals that are used as food preservatives. They are also found in some drinks and medications and can also be found naturally in some foods.

Some people are intolerant or sensitive to these chemicals. Sulphite sensitivity is common in people who have asthma, although it can also occur in people who do not have asthma. In people with asthma, sulphites can cause airway constriction. In rare cases it can cause life-threatening symptoms.

Common symptoms of sulphite sensitivity include:

  • Diarrhoea.
  • Coughing.
  • Wheezing.
  • Swelling of the skin.
  • Flushing of the skin.
  • Hives.
  • A blocked nose.

Sulphites must be declared on the packaging of any food in which they are contained or if sulphites were used during the processing of food.

Sulphites may be found in:

  • Dried fruit.
  • Canned vegetables.
  • Pickled foods.
  • Wine.
  • Apple cider.
  • Beer.
  • Tea.
  • Baked goods.

In the UK, food additives must be approved before they can be used. The FSA (Food Standards Agency) provides a full list of approved additives and E numbers. Approved additives are only usually allowed to be used in certain foods and the maximum quantities allowed will also be specified.

Coughing from food intolerance to sulphites


FOODMAPs are a group of short-chained carbohydrates that are found naturally in many foods. In some people who have a sensitivity, they can cause digestive distress including painful wind, bloating and discomfort. It is very common for people who have irritable bowel syndrome to have a FOODMAP intolerance.

Foods which are high in FOODMAPs include:

  • Milk.
  • Honey.
  • Soft cheese.
  • Apples.
  • Beans.
  • Lentils.
  • Bread.
  • Beer.

Other foods that people may be intolerant to include:

  • Eggs.
  • Artificial sweeteners used as sugar substitutes.
  • Food colourings.
  • Sugar alcohols.
  • Yeast.
FOODMAPs contained in bread

How to manage a food intolerance

Over-the-counter medications may help with symptoms of a food intolerance; however, they will not be able to cure or treat it. Antacids can help symptoms of heartburn or indigestion. Diarrhoea caused by a food intolerance can also be treated with over-the-counter medication. You should ask you pharmacist for advice as there are various medications used to treat this.

A medicine called Lactaid can help you to digest lactose and this is available over the counter.

Avoiding the food you are intolerant to will be the most effective way to manage your symptoms.

How is a food intolerance diagnosed?

A food intolerance is often diagnosed through an elimination diet. This is where foods that are most commonly associated with food intolerances are removed from your diet until any symptoms stop.

The foods are then reintroduced into your diet one at a time while any symptoms are monitored. The elimination diet may take 2-4 weeks when this is done properly and is usually done in several stages. It is best to do this with the support of a healthcare provider.

In stage one, a healthcare provider should help you prepare for the elimination diet. This could consist of keeping a food diary and monitoring your symptoms. You may then be able to identify foods that may be causing your symptoms. You should then have an eating plan, which is the least restrictive. It is important that the eating plan is followed strictly. If a food or ingredient is accidentally eaten, the process must be started all over again.

During stage two, the elimination diet will begin. When you have been symptom free for at least five days, stage three of the elimination diet can begin. This involves reintroducing eliminated foods one at a time. If a reintroduced food begins causing symptoms, you will need to log this in your food diary and cut this out of your diet again. In the final stage of the elimination diet, your healthcare provider will support you in creating a long-term eating plan, cutting out any foods that you are intolerant to.

Your healthcare provider will be able to advise you about alternative foods which will replace the ones you are intolerant to, ensuring that you are getting the vitamins and minerals you need to live a healthy lifestyle.

Intolerance to lactose can be diagnosed by using a lactose intolerance test, lactose breath test or a stool pH test.

If you think you may have a food intolerance, you should speak to your GP about what your testing and treatment options are.

How is a food intolerance treated?

Although having a food intolerance isn’t usually serious, it can negatively affect your quality of life and make you feel unwell. Your GP will be able to advise you of what your options are. This may include being referred to a dietitian.

You may be asked to keep a food and symptoms diary. You may be asked to follow a special diet where you avoid the foods you might be intolerant to. When your symptoms subside, you will be asked to gradually reintroduce the food you might be intolerant to and to see if your symptoms return. You may also be offered blood tests or a breath test if you think you are lactose intolerant.

You can purchase some home testing kits which claim to be able to diagnose a food intolerance; however, the NHS does not recommend that these are used as they may not be accurate and may lead you to cut out multiple foods, which may be harmful.

It is important not to cut food out of your diet without seeking advice from your GP as it could lead to you becoming deficient in important vitamins and minerals. This is especially important for children when they are growing and developing.

Whilst there is no cure or treatment for a food intolerance, treating the symptoms associated with a food intolerance is possible. Starting with an elimination diet and then modifying your diet long term, and avoiding the foods you are intolerant to, is considered to be the best treatment for a food intolerance.

In order to successfully avoid the food you are intolerant to, you can check labels and menus and it is usually easy to find a suitable alternative to whichever food you are intolerant to.

As the most common food intolerance is lactose, which is the natural sugar in milk, luckily there are many alternatives. Everyday Health provides a helpful guide for all milk substitutes available.


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About the author

Claire Vain

Claire Vain

Claire graduated with a degree in Social Work in 2010. She is currently enjoying her career moving in a different direction, working as a professional writer and editor. Outside of work Claire loves to travel, spend time with her family and two dogs and she practices yoga at every opportunity!

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