It is important to note that just because the body responds badly to a particular food, it doesn’t necessarily mean you have an allergy. Sometimes, another type of reaction to food called ‘food intolerance’ occurs.  According to NHS UK, food intolerances are defined as ‘difficulty digesting certain foods and having an unpleasant physical reaction to them’ (1). It is not known exactly how many people in the UK have a food allergy, however, population studies using conventional testing suggest that around 30 in 100 (30%) of people within the UK believe themselves to be intolerant to one or more foods (2).

Even with all the new ‘free from’ foods out there, it seems as though it has become easier than ever to manage food intolerances. However, in order for you to effectively manage food intolerances, understanding the basics is pivotal.

Food intolerance vs food allergy

Dairy products

Food intolerances do not involve the immune system, and they are generally not life-threatening. On the other hand, food allergies do involve the immune system and cause a specific immune response in the body which can be severe and life-threatening (3). People often mistake food intolerance for a food allergy as they often experience the same symptoms as a food allergy, but to a milder degree. The symptoms of food intolerance may look and feel like those of a food allergy, but they do not envoke an immune response. These are much more common and is the less serious of the two conditions.


Bowl of cereal

There are varying symptoms of food intolerances. According to NHS UK, the most common symptoms are:

  • Stomach pain
  • Bloating
  • Wind
  • Diarrhoea
  • Skin rashes and itching
  • Headaches
  • Nausea
  • Runny or blocked nose

What are the causes?

Bread and Cheese

There are various reasons why a person may develop a reaction to food. These may be due to things such as:

Enzyme deficiencies

Enzymes are needed to digest food. If some of these are missing or insufficient, this causes the digestion of that particular food to be impaired. For instance, some individuals who are lactose intolerant lack the enzyme lactase, which is needed to break down lactose (a sugar) in milk for absorption into the small intestine (4).

Chemical effects

Certain chemicals in foods such as amines in cheeses, and caffeine in coffee, tea, and chocolate can also cause intolerances. Some people are more susceptible to these chemicals than others (5).

Food additives 

With more foods containing additives to enhance their flavours, increase the appeal and lengthen shelf life, additives are becoming a very common cause of intolerance (6). Examples include antioxidants, artificial colourings, artificial flavourings, emulsifiers, flavour enhancers, preservatives and sweeteners. A small number are thought to cause problems including the following:

  1. Nitrates: Mainly found in processed meats, are known to cause itching and rashes (7)
  2. MSG (Monosodium glutamate): Often used as a flavour enhancer, is known to cause severe headaches (8)
  3. Sulphides: Commonly used in wines as a food enhancer or preserver
  4. Colourings: Carmine (red) and annatto (yellow), are known to cause food intolerance reactions
  5. Hot spices: Foods containing hot spices such as chilli or pepper, can cause irritant effects on the gastrointestinal tract (9)

Histamines in food

The natural occurrence of histamines in certain foods may also cause food intolerances (9). For instance, fish not stored properly can have an accumulation of histamine as they rot. This can lead to some individuals developing particular symptoms such as skin rashes, abdominal cramp, and diarrhoea.

There are also many other factors whose influence are not yet understood. Due to their varying causes, the effects are also diverse.  Reactions caused by intolerances can be severe but usually persist over a long period of time, are reoccurring and affect a range of bodily areas, and for this reason can be difficult to diagnose. Unlike food allergies, often large amounts of food may need to be ingested for adverse effects to occur.

Types of intolerances

cup of coffee

According to AllergyUK, the most common types of intolerances include:

  • Lactose (found in milk)
  • Gluten (often found in bread)
  • Monosodium glutamate (MSG)
  • Wheat
  • Caffeine
  • Alcohol
  • Artificial sweeteners
  • Histamine (found in Quorn, mushrooms, pickled and cured foods, and alcoholic drinks)
  • Artificial food colours, preservatives or flavour enhancers

Tips for Managing a food intolerance

Loaf of bread

1. Keeping a food diary

You could keep a food diary, noting:

  • What foods you eat
  • Any symptoms you have after eating these foods
  • When these symptoms come on
  • The timings that these symptoms occur

The data in the diary can help a dietician or doctor identify which foods are causing the reactions you may have, and what steps to take.

2. Trial elimination diet

Similar to diagnosing a food allergy, exclusion diets are extremely useful in isolating the culprit foods. In a typical exclusion diet, the suspected food is removed from the diet for a set period of time, usually between 2 weeks and 2 months. If during this period the symptoms resolve, then it can be eliminated from the diet.

If you are intolerant to a staple food in your diet, there are a plethora of alternative foods out there that can replace the food and provide you with the nutritional benefits you need. Seeking a suitable health consultant to help you identify alternatives could also be extremely beneficial.

Could my symptoms be something else?

Question mark

Sometimes, food intolerances could also be due to an underlying chronic condition. If you think you have an underlying condition, there is some soft research that you can do to check. Reading up on other conditions that cause similar symptoms to food intolerances such as the ones listed below could help you get a better understanding of what you may need to do to manage your intolerances.

If you regularly have the symptoms of food intolerances, but you’re not certain of the cause, it is important to see your doctor. They may be able to diagnose the cause of your symptoms and if necessary, carry out tests to determine whether it is due to an intolerance or another condition.

2 thoughts on “Food intolerances explained

  1. Thank you for this well written post. Completely agree on keeping a food diary, that’s how I found out that eatting certain types of cheese and nuts was part of my food intolerance issues as I would always shortly after face a skin reaction.

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