Food Intolerances and Allergies

Defining Allergies and Intolerances

Although the terms are sometimes used interchangeably, allergies and intolerances are not the same.

What’s the difference between food allergies and intolerances?

A food allergy is a reaction from your immune system that occurs soon after you have eaten or come into contact with certain foods.

It can happen immediately or after a short time, but is generally not long delayed. The reaction can also be triggered by very small amounts of food; in some cases, simply breathing in dust from the allergen can cause a reaction. Symptoms can include a skin rash, swelling, including in the mouth and throat (which can block the airway) and nausea. An extreme allergic reaction, known as anaphylactic shock, can occur in some people with food allergies. It affects all body systems and can be life-threatening.
A food intolerance is a more delayed reaction to a food or substance found in a food.

It is generally much less severe and immediate than a food allergy. Symptoms are often limited to digestive issues, although they can also include skin problems and headaches. It is reasonable to describe intolerances as the result of your digestive system failing to cope with something you have eaten.

In other words, allergies are reactions linked to your immune system. Like the reaction that you get when you are stung by a bee or wasp, or touch a nettle, they are rapid. They often result in swelling which can, if in the mouth or throat, potentially be fatal.

Food intolerances, on the other hand, are not potentially fatal, and people with intolerances are usually unaffected by consuming a small amount of the problem food (although the precise amount will vary). Intolerances can, however, be extremely uncomfortable, and can make people feel quite unwell, often over a long period of time, if undiagnosed.

The size of the problem

There is no question that food allergies are increasing.

In 1960, about 3% of Americans had a food allergy.
By 2018, this figure had more than doubled to 7%.

This increase has been paralleled by an increase in other conditions linked to allergies and the immune system, such as Crohn’s Disease and asthma.

Source: ZOE Science and Nutrition Podcast (2023). What’s the story with food intolerances?

Causes and triggers of allergies and intolerances

The precise cause of an allergy is often unclear.

Some studies have suggested that the problem is under-exposure: that people are more likely to be allergic to things that are new to their immune system. Allergies can also, however, be triggered by rapid over-exposure to the allergen in a sensitive part of the body (for example, if you are stung on the face or head by a wasp, you may become very allergic to wasp stings).

However, there is often no obvious trigger point, and people only become aware that they are severely allergic when they first react.

Allergies, age and endurance

Interestingly, allergies are not necessarily for life.

It is well-documented that you can develop allergies later in life. However, you can also ‘grow out’ of an allergy. This is especially likely with particular allergens, such as eggs.

Perhaps the best-known food allergy is to peanuts.

This is, anecdotally at least, on the increase. It is possible that peanuts and other nuts are simply becoming more common, because they are included in a wide range of processed foods. People are therefore more likely to be exposed to them than in the past, and become aware that they are allergic.

However, there are eight main food groups that are now believed to cause more than 90% of food allergies. These are eggs, milk-related products, wheat, soy, peanuts, tree nuts, fish, and shellfish. If you eat something that triggers an allergic reaction, it is most likely to be one of those products.

There are several clear potential causes of food intolerances:

People may lack the enzyme needed to digest the food. For example, lactose intolerance is often caused by not having a gene for the enzyme that digests it.
Sensitivity to food additives. Some people are more sensitive to certain chemicals than others, and this can cause problems when they are added to food. Examples include food colouring and sulphites, which are used in drying fruit.
People with coeliac disease are unable to digest gluten properly, and are therefore intolerant of it.
There may also be psychological factors involved in food intolerances. For example, some people are simply unable to swallow certain foods, without any obvious physical cause.

Identifying Food Allergies

Food allergies are severe enough that identifying their existence is often not hard. However, identifying the trigger can be more difficult, not least because you cannot risk anaphylactic shock to do so.

The key to treating allergies is often avoidance, so it is important to identify the allergen as early as possible.

Identifying allergens

There are two main tests for allergens:

A ‘scratch test’, where the skin is exposed to a small amount of potential allergens to test for a reaction; and
A blood test, which can be used if a skin test is not appropriate.

Those who have experienced a severe allergic reaction should therefore discuss this with a doctor, to have a test for potential allergens as soon as possible.

These tests not only identify the allergen, but also give an idea of the intensity of the reaction, which helps to provide information about how to manage it.

Managing Food Allergies

The usual way in which food allergies are managed is by avoiding the trigger foods.

You should, for example, check labels to ensure that processed foods do not contain your allergen. If you are eating out, you should ask the restaurant or café about potential allergens, because not everything is listed on the menu.

When your reaction is very severe, you may need to do more than simply avoid eating that particular food. For example, it may be necessary to ask schools or workplaces to ensure that they are ‘nut-free’ for the safety of a particular individual, and you may also need to inform airlines when flying.

In severe cases, your doctor may suggest a ‘controlled exposure’ approach to allergens, also known as immunotherapy. This means that individuals with allergic reactions are exposed to very small amounts of the allergen over a long period. This builds up their tolerance and reduces the level of the allergic reaction. This is generally only done with very severe, life-threatening immune reactions, because the treatment itself carries risks.

Pregnancy, eating and child allergies

For many years, the advice was clear: avoid potential allergens like shellfish and peanuts during pregnancy, and don’t give these foods to small children (under the age of about two years old).

It was thought that this would help to prevent children from developing allergies to those foods.

However, we now know that this advice was wrong.

Instead, it seems that you should continue to eat these foods during pregnancy, and also introduce them—along with a wide range of other foods—from a relatively early stage in childhood. Nobody is saying that prawns and peanuts should be the first foods that you use for weaning—but you should not avoid them when you start to introduce a wider range of foods into your child’s diet.

You may find it helpful to read our pages on Pregnancy and Weaning Babies.

If you are exposed to the allergen, and it triggers a reaction, this can usually be treated with anti-histamines taken orally. This includes for vomiting and skin conditions. Skin conditions can also be treated with antihistamine creams.

Serious allergic reactions (including anaphylaxis), however, require rapid treatment with adrenaline to prevent potentially fatal consequences.

Most people who are severely allergic to something, including a food, are aware of their allergy and carry an adrenaline pen (sometimes called an ‘EpiPen’). Even after treatment, they should still seek medical advice as soon as possible after having an allergic reaction.

Identifying Food Intolerances

Identifying food intolerances may be less critical than allergies, but it is also harder. There is unlikely to be an immune reaction involved, and therefore there are few, if any, definitive tests.

There are two main ways to identify triggers: using a food diary, and removing and replacing certain foods. The most usual approach is likely to involve both.

Using a food diary to identify potential triggers

WARNING! This is best done under the supervision of a trained dietician or nutritionist, who is more likely to be able to identify likely triggers. However, as a first step, you can do this yourself.

Over a period of several weeks or a month, keep a diary that sets out everything you eat, right down to a biscuit and a cup of tea or coffee, and the precise time.
Also keep a note of any symptoms that you have, including minor ones, and the time at which they occurred.
Try to spot any patterns that are emerging. Are there certain foods, combinations of foods, or even ingredients that seem to cause you particular problems?
- WARNING! Triggers are not always obvious, and it helps to be aware of the ingredients of what you eat. It is easier to do this when you cook your own food, rather than eating ready meals or eating out.
If you spot a potential trigger, try cutting it out of your diet for a few days and see what happens.
You may find that you have more than one trigger. For example, some people are both lactose- and gluten-intolerant.

When a food intolerance is very severe, nutritionists sometimes advise cutting a wide range of potential triggers out of your diet all at once. This is designed to allow the symptoms time to settle, before you add back in potential triggers one at a time, to see which ones have an effect.

WARNING! This is not something to try at home without the supervision of a qualified healthcare professional.

It can lead to problems such as becoming malnourished if you do it for too long. It can also mean that underlying conditions are not diagnosed.

Managing Food Intolerances

The traditional approach to managing food intolerances has been to cut that particular food group out of your diet.

However, this has not proven entirely effective—and it also means that your diet becomes increasingly restricted as you cut out more potential triggers. It is particularly ineffective to start to eat more processed food to try to cut out substances like lactose or gluten.

A better understanding of the role of our gut bacteria or microbiome has helped both to explain this, and provide an alternative way of managing intolerances.

A food intolerance basically means that you lack the enzymes necessary to digest one or more particular substances in food. However, your gut bacteria can often take over that role—although they may need some training. If, for example, you cannot digest lactose, you can ‘train’ your gut bacteria to do that instead, increasing your tolerance. You simply start with small quantities, and gently increase them when it is comfortable to do so. This ‘repairs’ your gut microbiome, and ensures that it is capable of helping you again.

However, it is important to be clear about what substance is causing the problem. You therefore need to go through a process of identifying triggers (both substances and amounts) before you can start to address the issue.

WARNING!

Gluten intolerance is often caused by coeliac disease, and this cannot be resolved by ‘training’ your gut bacteria.

It is therefore important to be clear that you do not have coeliac disease before you start reintroducing foods.

The only way to find out is by a proper diagnosis by a medical professional, and this often requires an endoscopy or genetic testing. Blood tests are not always reliable.

A Side Issue? Food Allergy vs. Histamine Intolerance

Allergic reactions are caused by our bodies reacting to an excess of histamines.

However, some people are simply less tolerant of histamines. This means that their bodies react to histamines at much lower levels than other people. They are not necessarily allergic to particular substances—they are simply less tolerant of histamines. The problem is that some foods contain higher levels of histamines—and therefore may trigger the symptoms of histamine intolerance. These foods include anything that is fermented, or includes the products of fermentation, such as alcohol or vinegar, and also food that is just starting to go ‘over’: it is not ‘off’, and most people could eat it without any trouble, but it is not entirely fresh.

Almost all animal products (meat, fish, shellfish etc) are potential problems, because of their tendency to go off. Plant foods that are most likely to be a problem are spinach, aubergine, tomatoes and avocados.

Unfortunately, the symptoms of histamine intolerance are very similar to the symptoms of food allergies. Indeed, the most common symptom of histamine intolerance is actually bloating.

If, therefore, you get the symptoms of a food allergy, but with a much wider range of foods—and often NOT foods in the eight groups that are the key triggers of allergy—this may be a sign of histamine intolerance.

Treating histamine intolerance

Dr. Will Bulsiewicz, gastroenterologist and author of The Plant-Fed Gut: Empower Your Health recommends a very simple solution for anyone experiencing histamine intolerance.

He suggests that you should allow peas to sprout on your windowsill—or better still, in the dark—and then eat them.

The reason is that they produce an enzyme called diamine oxidase, which breaks down histamine. Simple, cheap, but effective.

The bottom line

The best advice if you think you may be suffering from a food intolerance or allergy is to talk to your doctor, and ask for a referral to a specialist clinic.

They are best-placed to help you identify the trigger, or any underlying condition, safely.

Continue to:
Dieting for Weight Loss
Understanding and Improving Your Gut Microbiome