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Food intolerances can be experienced by many different people in many different ways, with symptoms such as bloating, constipation, distention, wind, pain and discomfort.

If you’re looking to stay on top of your overall and heart health, it may be worth looking at the food you’re eating.

Food intolerances versus food allergies

Not to be confused with a food allergy, food intolerances are wide and varied. However, besides causing discomfort and decreasing quality of life, they don’t affect your health. Below are the main differences between a food intolerance and a food allergy.



Does not involve an immune response

Triggers an immune reaction

Not life threatening

Can be life threatening

Often dose dependant

Usually not dose dependant

Generally just affects the digestive tract

Can affect all organ systems

Higher prevalence

Lower prevalence

Reaction caused by a food carbohydrate or chemical

Reaction caused by a food protein

Reactions may be immediate but more likely to take 12–24 hours to develop

Reaction is immediate after consumption or contact with food


  • Diarrhoea
  • Bloating/wind
  • Distention/discomfort
  • Constipation
  • Red/itchy skin
  • Headache/migraine


  • Itching, burning, swelling
  • Runny nose
  • Skin rash
  • Hives
  • Vomiting/nausea
  • Breathing difficulties, eg, wheezing

The best way to describe the difference between a food allergy and food intolerance is to think about the different reasons some people can’t drink milk.

Some people can’t drink milk because they are intolerant to the natural sugar (carbohydrate) in milk called lactose. They lack a sufficient amount of the enzyme lactase to break down the lactose and digest it. As such, lactose remains undigested in the large intestine causing bloating, pain and diarrhoea.

Some people can’t drink milk because they are allergic to the protein portion of milk. The reaction is caused by the immune system being activated by the presence of the protein in the gastrointestinal tract. Depending on the severity of the allergy, people experience a range of different reactions from mild to severe.

The varying reasons in these two examples make a big difference to how the individual manages their intake of milk. A person with lactose intolerance can happily consume lactose-free milk or just consume small amounts of milk at a time and manage their symptoms that way. A person with a milk protein allergy may not be able to drink milk at all and needs to find a suitable milk replacement in consultation with a qualified dietitian.

Common causes of food intolerance

  • Absence of an enzyme needed to fully digest a food – eg, a lack of the enzyme lactase to digest the milk sugar lactose
  • Irritable bowel syndrome (IBS) – this is a common diagnosis of unclear food intolerances, most likely caused by a hypersensitivity to gases produced by bacteria in the gut
  • Sensitivity to food chemicals – natural and added
  • Recurring stress or psychological factors – the digestive tract is highly susceptible to stress and your psychological state

Common foods that people are intolerant to


FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols. These are types of carbohydrates found naturally in many foods and can be added to others.

A lot of research has been done over the past 10 years or so, with findings that a low FODMAP diet is the best way to manage symptoms of IBS and help people discover exactly which foods they’re intolerant to. People are rarely intolerant to all FODMAPs. By the time the person has completed the Low FODMAP diet and challenge protocol with their dietitian, they know exactly which foods to limit or avoid in order to minimise their symptoms.

Many individuals feel they may be intolerant to gluten. However, this needs to be interpreted with caution. Gluten is a protein, not a carbohydrate. As such, it doesn’t cause problems in your digestive tract unless you have coeliac disease. With coeliac disease, gluten activates your immunes system – it is an allergy, not an intolerance.

What is interesting about a suspected ‘gluten intolerance’ is that many gluten-containing foods contain fructans, an oligosaccharide or FODMAP. This is much more likely to be causing the symptoms. It may be that you can tolerate a small amount of gluten (eg, one small cracker) but a whole sandwich (two slices of bread) is too much. If you can have small amounts of gluten-containing foods but not large amounts, or only some gluten-containing foods trigger your symptoms, gluten is not likely to be the culprit – it’s possibly something else.

Food chemicals

Food is a mixture of thousands of different types of chemicals, natural and added. Some people are not able to tolerate large amounts of these chemicals. Once they reach their ‘threshold’, they can experience a myriad of different symptoms.

This is a complex area of nutrition, so if you suspect that you are affected by food chemicals, consulting an accredited practicing dietitian experienced in this area is the best place to start.

Suspect a food intolerance?

Don’t self-diagnose.

You may think you can pinpoint exactly what food is causing your symptoms, but unless you’re eating that food (or ingredient) in isolation, then you really can’t be sure. This is especially true with food intolerances.

Many symptoms of food intolerance happen in the lower digestive tract (large intestine), which takes food 12–24 hours to get to after being eaten. If you experience symptoms straight after a meal, it’s not likely that meal that caused the symptoms. That meal simply caused the food in your whole digestive tract to move along. The food you ate the day before is most likely what is giving you grief now.

A qualified dietitian uses systematic processes such as food symptom journals and elimination diets to help you clearly identify the exact cause of your symptoms. This will help ensure you don’t eliminate foods unnecessarily, and help keep your diet as varied as possible. A well-balanced, varied diet is the biggest predicator of health, more than anything else.

Improving overall diet quality – a good place to start

To improve overall diet quality, choose more whole foods, increase intake of vegetables and fibre, and reduce intake of processed foods high in sugar, fat and salt and low in nutrients like vitamins and minerals.

Some people may be able to clear up the majority of their gut symptoms by simply eating a better-quality diet, meeting their daily fibre needs, upping their intake of vegetables, drinking more water and getting more regular exercise.

Never underestimate what small, consistent changes to your diet and lifestyle can do for you. If you’re ever confused about what changes might be beneficial for you, seeing a qualified nutrition professional is the best place to start.

Header image: Pixabay

About the author

The Healthy Eating Hub

This article was written by an Accredited Practicing Dietitian from The Healthy Eating Hub. The Healthy Eating Hub is a team of university-qualified nutritionists and dietitians who are passionate about helping people develop long term healthy eating habits through offering evidence-based and practical nutrition advice that people can put into practice straight away.


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