Food intolerances can lead to a variety of digestive symptoms, such as bloating, excess gas, and nausea. They are different to allergies because they don’t trigger an immune response.

Identifying a food intolerance can be difficult, in this article we’re going to look at what food intolerance is and how you can understand if you have one.

What is food intolerance?

Food intolerance is difficulty digesting certain foods, although it’s not a life-threatening condition, it can make those suffering from it feel extremely unwell, having a major impact on their day-to-day lives.

Food intolerances vs food allergies

Food intolerance isn’t the same as a food allergy. Although they have symptoms in common, food intolerances do not affect the immune system as allergies do.

A food allergy:

  • Results from an immune system reaction where it treats proteins found in food as a threat
  • Can trigger an allergic response quickly after exposure to a small amount of food such as skin rashes, trouble with the respiratory system, and swelling
  • Is often linked to specific foods such as fish, milk, and nut allergies
  • Can be severe or life-threatening

A food intolerance:

  • Does not involve the immune system and is not considered life-threatening or severe
  • Is often triggered by the amount of food a person has eaten
  • Can be caused by a variety of foods
  • Often affects the digestive system

Food intolerance symptoms

A person suffering from food intolerance will usually experience discomfort after eating certain foods. The symptoms are varied depending on each person however they usually involve the digestive system.

Common symptoms of food intolerances include:

  • Abdominal pain and bloating
  • Headaches
  • Bowel symptoms such as diarrhoea and excess gas
  • Skin rashes and itching

Common food intolerances

If you are unsure which foods you are intolerant to, it can be helpful to avoid foods that commonly cause food intolerances such as dairy and gluten. Below, we take a look at some of the most common food intolerances and their symptoms.


Lactose is the sugar found in dairy products. It’s broken down in the body by the enzyme lactase, which is needed for lactose to be properly digested and absorbed by the body.

Lactose intolerance is incredibly common and is caused by a lack of these enzymes, which help to digest lactose in the body. This is what causes discomfort.

Common symptoms of lactose intolerance include:

  • Abdominal pain and bloating
  • Bowel symptoms such as diarrhoea and excess gas
  • Nausea


Gluten intolerance is highly common and is caused by an adverse reaction to gluten, which is the protein found in wheat. There are three main forms of gluten intolerance including celiac disease, non-celiac gluten sensitivity, and wheat allergies.

Celiac disease is classed as an autoimmune disease as it involves an immune response, and wheat allergies are similar. Many people experience intolerances to gluten without being allergic to it and this is known as non-celiac gluten sensitivity, which is less severe than celiac disease.

Common symptoms of gluten sensitivity include:

  • Abdominal pain and bloating
  • Bowel symptoms such as diarrhoea and excess gas
  • Headaches
  • Fatigue
  • Skin rash

It’s not always food that causes sensitivities. The culprit could be lurking within the food and may be a food additive or chemicals such as caffeine, fructose, and MSG.


Caffeine is a chemical that is found in a variety of drinks and foods. It reduces fatigue and increases alertness when ingested. Most adults can safely consume up to 400mg of caffeine every day without side effects, but some people aren’t so lucky and experience adverse reactions even after just one cup of coffee.

This sensitivity to caffeine is largely linked to genetics, and people with caffeine sensitivity are likely to experience:

  • Anxiety
  • Increased heartbeat
  • Insomnia
  • Restlessness


Fructose, a natural sugar found in fruits and vegetables as well as sweeteners like honey, can also cause problems with the digestive tract.

A fructose intolerance means that your body cannot absorb it efficiently into the blood which causes digestive issues such as tummy pain.

The main symptoms of fructose malabsorption are:

  • Acid reflux
  • Diarrhoea and nausea
  • Bloating
  • Tummy pain


It can be difficult to know whether you have a food intolerance as these common symptoms are typical of many other conditions however there are a few things you can do to understand whether your symptoms are from food intolerance or could be something else.

food diary

Keep a food diary

Keeping a food and symptom diary is a great way to help you identify when your symptoms flare up and what foods trigger a reaction. It can also help you to identify if it makes any existing conditions worse such as irritable bowel syndrome or rashes.

Keeping a food diary doesn’t have to be complicated, you just need to ensure that you stick to it and track each day over a set period of time:

  • The foods you eat
  • Any symptoms you have after eating these foods
  • When these symptoms happen

Doing this should help you identify food intolerances, or pinpoint the food additives that make you feel poorly.

Elimination diet

Another great way to help you identify which foods may be causing your symptoms is by excluding them from your diet. Elimination diets work by taking out potential problem foods one at a time and observing the effect it has on you.

If you suspect that you have a gluten intolerance, for example, try cutting any foods that contain gluten out of your diet for a month to see if your symptoms improve. After a month, you can then re-introduce these foods to see if your symptoms return.

Food intolerance test

If you have tried the two methods above but are still unsure what is causing you to have an unpleasant physical reaction, then you should book in for a food intolerance test.

What is a food intolerance test?

Food intolerance tests are non-invasive tests to check how your body responds when you eat a particular food. It looks for the antibody immunoglobin G (IgG) from a finger-prick blood sample.

An increase in IgG antibodies after eating particular foods indicates intolerance to that food.

Why get a food intolerance test?

The great thing about a food intolerance test is that unlike the elimination diet and food diary, you can accurately get a diagnosis so that you can take control of your food intolerance sooner and cut out or reduce offending foods.

Living with a food intolerance

If you have been diagnosed with food intolerance, there’s no doubt it is going to have a significant impact on your life as you may find you have to skip social occasions or be more mindful when out at a restaurant.

The best way to live alongside a food intolerance is to track your symptoms and understand how much of one food causes an adverse reaction.

For people who suffer from gluten and lactose intolerances, there are a variety of gluten-free and lactose-free alternatives on the market so that you can continue to enjoy your favourite meals.

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