This is very simplified information about food intolerances – there are more resources available at the end of each section for further reading for those who are interested in knowing more.
The intolerances covered briefly on this page are histamine, sulphites, salicylates, lectins and lactose. We also look at FODMAP foods and Non Coeliac Gluten Intolerance.
Food Intolerances are caused by problems with the metabolic system which usually means there is an enzyme deficiency which causes certain chemicals to build up in the body as they are not being processed, digested or removed properly. You are more likely to be suffering from a food intolerance than an allergy. The most studied food intolerance is lactose intolerance, which is more common in adults and can start to occur from any age.
Intolerances are most commonly confused with non-IgE food allergies. Even though many of the symptoms are incredibly similar this type of allergy is immune mediated (caused by a problem with the immune system), even though symptoms are delayed people can suffer from serious allergic reactions including anaphylaxis. The most studied form of non-IgE food allergy is FPIES (Food Protein Induced Enterocolitis Syndrome), which is common in babies and can be outgrown.
An IgE food allergy is also immune mediated but by IgE antibodies. This causes the classic immediate reactions and are more likely to be severe.
What is histamine?
Histamine is a hormone which is made by the body in response to injury or allergic reaction, causing the body to swell and/or itch. Histamine is a natural hormone and is an essential part of a normal functioning immune system.
What causes a histamine intolerance?
Histamine is found in most foods in some portions and is a chemical made in our own bodies. People with a histamine intolerance generally have symptoms of gastrointestinal discomfort and skin irritation. An antihistamine can improve symptoms but switching to a low-histamine diet can be beneficial. Histamine intolerance is caused by people who are unable to make an enzyme called diamine oxide, commonly referred to as DAO. This enzyme breaks down excess histamine in the body. Some medications inhibit DAO production, this type of intolerance is temporary, the effects can be limited by modifying your diet.
Histamine and Scombroid Poisoning
Scombroid poisoning is a term for a specific type of food poisoning which has similar symptoms to an allergic reaction due to an increase in histamine in the body. The amount of histamine in fish starts to increase once it is caught, so improperly handled and refrigerated fish can have quite high levels of histamine in. This is temporary and a bout of this type of food poisoning should not affect you further once the histamine has been processed from your body.
How common is histamine intolerance?
A 2007 study suggested that histamine intolerance is uncommon at 1% of the population, but of this 1% most of the sufferers were middle aged or older, which suggests inhibition of the enzyme DAO from medication as the most common cause.
Diagnosis and Testing
There is no reliable testing for histamine intolerance, it is recommended you visit your doctor with a completed intolerance diary. Your doctor may want to do allergy testing to rule out an IgE food allergy and further testing to rule out any gastrointestinal disorders. A completed food diary and then a reduced histamine diet diary with proven reduction in symptoms should be enough to get a diagnosis of histamine intolerance.
There is lots of information out there about reducing histamine in your diet – but if you are not DAO deficient, this is not essential. Your body has natural ways to flush histamine from your system.
Allergy UK - Histamine Intolerance
Healthline - Histamine
Histamine Intolerance: The Current State of the Art
What are sulphites?
Sulphites are inorganic compounds used to preserve foods. The terms sulphites and sulfites can be used interchangeably, but in the UK they are known as sulphites.
What causes a sulphite intolerance?
Sulphites in food slowly release sulphur dioxide, which inhibits the growth of bacteria, helping food and medications last longer. An intolerance is when the sulphites irritate the gastro-intestinal tract when sulphur dioxide is released, causing the common symptom of asthma exacerbation.
How common is sulphite intolerance?
Sulphites are thought to affect 2% of the population, but this increases to 5 to 13% in people who suffer with asthma.
Diagnosis and Testing
There is no reliable testing for sulphite intolerance, it is recommended you visit your doctor with a completed intolerance diary. A completed food diary and then a reduced sulphite diet diary with proven reduction in symptoms should be enough to get a diagnosis of sulphite intolerance.
The misinformation on this intolerance is not as widespread as some of the others. It is most likely seen in terms of wine and beer making, it is more ‘trendy’ to make sure wines are sulphite free rather than essential as it affects such a small portion of the population.
To find out more about this intolerance please visit the dedicated Sulphite Page
ASCIA - Sulfite Sensitivity
Allergy UK - Sulphites
Food Allergy Canada - Sulphites
Adverse reactions to the sulphite additives
Anaphylaxis UK - Sulphites Fact Sheet
Considerations for the diagnosis and management of sulphite sensitivity
What are salicylates?
Also called salicylic acid, these are natural chemicals produced by fruit and vegetables as a defence mechanism against insects and disease. Extracts from these chemicals are used in medicines like aspirin in much larger quantities, so are more likely than food to cause symptoms.
What causes a salicylate intolerance?
The most likely cause of a salicylate intolerance is an enzyme deficiency of cyclo-oxygenase, which regulates the production of leukotrienes. Leukotrienes are lipid mediators, when they build up in the body they can cause gastrointestinal and respiratory symptoms including worsening of asthma symptoms.
How common is salicylate intolerance?
Salicylates sensitivity is thought to be as low as 2% of the population.
Diagnosis and Testing
There is no reliable testing for salicylate intolerance currently. It is recommended you visit your doctor with a completed intolerance diary, making sure you include any reactions to salicylate containing medicines or products (like toothpaste).
The misinformation on this intolerance is not as widespread as some of the others, avoiding salicylates for non-medical reason would drastically reduce the variety in your diet as it is found in a variety of fruits and vegetables.
To find out more about this intolerance please visit the dedicated Salicylates Page
Web MD - High Salicylate Foods
Natural Library of Medicine, 2019, The Role of Leukotrienes as Potential Therapeutic Targets in Allergic Disorders
Allergy UK - Aspirin Intolerance and Salicylates FactSheet
Drugs.com - Salicylate Drugs
What are lectins?
Also called hemagglutinins, they are carbohydrate binding proteins, some of them can function as IgE allergens like hevein, chitinases and wheat agglutinins which can also be problematic for those with coeliac disease.
What causes a lectin intolerance?
Eating foods high in lectins without cooking them can cause gastrointestinal symptoms as they are very difficult to digest and irritate the gut.
How common is lectin intolerance?
Lectins are not well studied as a group, probably since they contain allergenic sub-groups of their own. Coeliac disease affect 1% of people and less than 1% of people are allergic to latex (with only 30% of people with latex allergy also have latex food syndrome). It is likely that this is not very common at all.
Diagnosis and Testing
There is no reliable testing for lectin intolerance, it is recommended you visit your doctor with a completed intolerance diary.
Avoiding lectins completely can reduce the amount of protein and fibre in your diet, so is only necessary if you are very sensitive to lectins.
To find out more about this intolerance please visit the dedicated Lectins Page
Harvard - Antinutrients - Lectins
Are Dietary Lectins Relevant Allergens in Plant Food Allergy?
Healthline - Lectins
What is lactose?
Lactose is a sugar found in milk and in many products containing dairy unless stated.
What causes lactose intolerance?
Lactose intolerance is caused by reduced amounts of an enzyme called lactase which aids in the digestion of the sugar lactose. Usually, lactose would be digested in the intestines and be broken down before it makes it to the bowel. In lactose intolerance poor digestion means lactose ends up in the bowel where normal bacteria interact with it causing painful gastrointestinal symptoms.
How common is lactose intolerance?
By far the most common form of food intolerance, up to 65% of the world’s population is lactose intolerant. The ability to make sufficient amounts of lactase is genetic, so while lactose intolerance is high in some populations it is much lower in others, for example in Northern Europe it is thought to be as low as 5% (some sources suggest just 8% in the UK).
Diagnosis and Testing
It is recommended you visit your doctor with a completed intolerance diary, you can have blood tests which confirm lactose intolerance or do a hydrogen breath test which can indicate if you are digesting lactose properly.
There have been claims that raw milk (which is unpasteurised) does not cause symptoms of lactose intolerance, this is unfounded, most forms of dairy will contain lactose unless they have been processed to remove it.
To find out more about this intolerance please visit the dedicated Lactose Page
NHS - Lactose Intolerance
Mayo Clinic - Lactose Intolerance
Healthline - Lactose Intolerance
What are FODMAPs?
FODMAP stands for f
olyols. They are short-chain carbohydrates that the small intestine doesn’t absorb well. FODMAP diets were created to help people with irritable bowel syndrome (IBS).
What causes an intolerance to FODMAP foods?
Short-chain carbohydrates are essentially sugars, when they are digested, they attract water and then ferment in the digestive system due to gut bacteria. This is the same for everyone, but people with IBS and other gastrointestinal issues take longer to digest foods for multiple reasons. The sugars sit in the bowel and intestines for longer and cause excessive pain and bloating.
How common is FODMAP intolerance?
10 to 20% of the population suffers from Irritable Bowel Syndrome affected by high FODMAP foods.
Diagnosis and Testing
An intolerance to high FODMAP foods cannot be tested, but it is recommended you visit your doctor with a completed intolerance diary if you think certain foods are affecting your digestive system. IBS can often be confused for coeliac disease and other gastrointestinal conditions, so it is advised to contact your doctor to rule out more serious conditions like bowel cancer.
Low FODMAP diets are designed to help improve gastrointestinal symptoms and were never intended to be a full time diet to follow. You are meant to reduce high FODMAP foods, then slowly incorporate them back into your diet, removing any that cause problems when reintroduced. A continued low FODMAP diet with no reintroduction attempts of food can lead to a poor diet.
To find out more about this intolerance please visit the dedicated FODMAP Page
Monash University - FODMAPs
Healthline - FODMAPs
BBC Good Food
The IBS Network
NHS - Irritable Bowel Syndrome
Non-Coeliac Gluten Intolerance (NCGI)
What is gluten?
Gluten is the name given to a group of proteins (also known as prolamins). It is most commonly thought of as a food protein which cause coeliac disease (celiac).
What causes NCGI?
Although NCGI is now being studied more frequently the cause of it is currently unknown. It is likely, as with other intolerances, that is due to a lack of a single or combination of digestive enzymes which makes gluten hard to digest causing irritation in the bowel.
Why is it different to Coeliac Disease?
Coeliac Disease is not an allergy, but an auto immune disorder. Coeliac Disease can be diagnosed with a blood test and a food allergy to wheat can also be identified by a blood test. Scans with coeliac patients can show damage to the gut. In comparison NCGI is often diagnosed when a food diary shows you are still suffering symptoms after eating gluten but other tests have come back negative, there is no damage to the gut in diagnostic scans and you get more non-GI symptoms like brain fog, fatigue and joint pain than classic coeliac disease.
How common is NCGI?
As it is only recently being studied current estimates for how many people suffer from this intolerance is 1 to 3%.
Diagnosis and Testing
There is currently no reliable testing for NCGI, it is recommended you visit your doctor with a completed intolerance diary and test for coeliacs or wheat allergy by blood test. For Coeliac testing you must still be eating wheat for confirmation of this condition.
NCGI is dismissed by some as psychological in nature rather than physical. It is currently being studied as a separate condition to see what the mechanism of the intolerance is.
To find out more about gluten please visit the dedicated Gluten page
Coeliac UK - Gluten Sensitivity
Beyond Celiac - Non-celiac gluten sensitivity
Healthline - Gluten Intolerant