Introduction

Food intolerance may not necessarily cause autoimmunity, but some people with autoimmune disorders may have their symptoms worsened by certain foods.¹

Unfortunately, little is known about the link between food intolerances and autoimmune diseases.² However, there is extensive research on how gluten causes coeliac disease and more recently, how other molecules in gluten-containing foods may be involved in non-coeliac gluten sensitivity (NCGS).^1,2

Read on to find out more about food intolerance, gluten, leaky gut syndrome, and the associated autoimmune disorders.

Food intolerance

What is food intolerance?

Food intolerance occurs when the body finds it difficult to digest certain foods, ingredients, or food additives.³ Usually, this is not a serious problem, unlike food allergies, where the immune system reacts to specific foods and can result in anaphylaxis in severe cases.

In most cases, when people report new symptoms related to a specific food, it is an intolerance, not an allergy.

Common types of food intolerances include:⁴

• Lactose found in milk and dairy products (e.g., cheese and yoghurt)
• Gluten is found in wheat, barley, rye (e.g., bread and pasta), and sometimes in oats due to manufacture cross-contamination 
• Histamine found in matured cheese, wine, and smoked meat
• Caffeine found in coffee, tea, some energy drinks, and fizzy drinks
• Alcohol
• Sulphites found in wine, beer, and cider
• Salicylates found in some vegetables, fruits, spices, and herbs
• Monosodium glutamate (MSG) found in ripe fruit, savoury foods, and cured meats

What causes food intolerance?

Food intolerance is believed to cause symptoms through two mechanisms:²

• Enzyme deficiency – the body doesn’t have enough of or lacks the required enzymes to digest a nutrient
• Leaky gut syndrome – an unhealthy intestinal wall may have larger holes than normal, letting partially digested food, toxins, and microbes enter the tissues beyond the digestive tract

Diagnosis of food intolerance

Your GP may refer you to a dietitian for specialist nutrition diagnostics and advice. 

Here are some methods used to find out what type of food intolerance you may have:

• Elimination diet – your doctor creates a diet plan where foods you may be intolerant to are eliminated to see if your symptoms improve. After a few weeks, these foods are reintroduced one by one to see if the symptoms return.
• Blood tests – often used in conjunction with an elimination diet to check for inflammatory mediators (indicators of intolerance) when reintroducing different foods into your diet.
• Breath test – used only for lactose intolerance.

Food intolerance tests are also useful tools in autoimmune patients. They help tailor diets for each individual, relieving symptoms, and slowing or completely halting the autoimmune response.¹

Important to note: Many tests on the market claim to diagnose food intolerances. There is scarce evidence for their accuracy, and they are not recommended for medical diagnosis. Always seek medical advice from your GP.

Treatments

There are various ways to cope with food intolerances.

• Try an elimination diet – reduce or avoid different foods to find out what is causing the reaction and associated symptoms. Then create a personalised diet that excludes foods that worsen or cause your symptoms.
• Read labels on food packaging to check for ingredients you are intolerant to.
• Take over-the-counter medicines when symptoms occur, such as antidiarrhoeals or antacids.

It is not recommended to completely remove multiple foods from your long-term without medical supervision, as this can lead to deficiencies in important nutrients, vitamins, and minerals. Seek the approval of a GP or a dietitian.

Your doctor may be able to replace a food with a different source of the same nutrients, give you an enzyme supplement, or advise you to simply eat less of it. They may also recommend a probiotic to reinstate a healthy gut microflora or medication for your autoimmune disorder.

Autoimmune disorders

Autoimmune diseases occur when the immune system mistakenly attacks your own body cells.

When immune cells encounter a certain food, they may produce antibodies against it, creating an immune reaction. If this food contains proteins on its surface similar to your cells, the immune system develops an autoimmune reaction, where the immune system attacks your body.

The link between food intolerance and autoimmune disorders

Shared symptoms

Symptoms common to food intolerance, coeliac disease, and non-coeliac gluten sensitivity include:

• Flatulence
• Bloating
• Diarrhoea
• Constipation
• Stomach pain
• Headache
• Tiredness
• Vomiting

Effect of food intolerance on autoimmune disorders

An observational study found a clear difference in “food intolerance profiles” between autoimmune patients and people without autoimmunity.¹ Autoimmune patients had a considerable reaction to several foods, as observed by the increased levels of specific antibodies to:

• Casein
• Cow milk
• Wheat
• Gliadin
• Egg white
• Rice

Some, but not all autoimmune patients reacted to nuts (e.g., walnuts or almonds). No reaction was observed for vegetables, fish, and meat products. The study also suggests food intolerances can exacerbate symptoms in autoimmune patients.¹

Overall, there is limited research on the link between food intolerances and autoimmune diseases. However, extensive research has shown how gluten causes coeliac disease and how gluten-related products may be involved in non-coeliac gluten sensitivity.¹

Gluten and leaky gut syndrome

With the recent simultaneous increase in overall gluten intake and cases of autoimmune diseases, scientists have taken an interest in studying the adverse effects of gluten on autoimmune disorders.⁵

What is gluten?

Gluten is made of prolamin proteins, varying in structure and properties between the four foods:

• Wheat
• Barley
• Rye
• Oat 

These proteins are highly resistant to breakdown by enzymes in the gastrointestinal tract, which can lead to the development of gluten intolerance in genetically predisposed individuals.⁴

Leaky gut syndrome

Gluten can induce leaky gut syndrome. This is where the intestinal wall becomes more permeable, letting bacteria, food particles, and toxins enter the tissues beyond the digestive tract. It results in inflammation and changes the gut microflora, leading to digestive and extra-digestive symptoms, as mentioned in the “shared symptoms” section above. Increased inflammation worsens autoimmunity symptoms.^5,6

The gut microbiota composition changes based on one’s diet.⁷ Depending on the composition, the effects of food vary. A red meat, dairy or egg-rich diet, for example, promotes the growth of certain microbial species. The microbes then break down this food and produce waste products. For example, one such waste product, called trimethylamine-N-oxide (TMAO), can accumulate in organs or blood circulation, increasing inflammation and worsening symptoms of autoimmune disease.⁷

Here are some factors that influence the development of a leaky gut:⁶

• Imbalance in the gut microflora population
• Overgrowth of yeast
• Use of non-steroidal anti-inflammatory drugs (NSAIDs)
• Alcohol consumption
• Systemic inflammation
• Stress
• Some infections (e.g., human immunodeficiency virus (HIV))
• Antibiotics
• Dietary patterns

Gluten intolerance-related disorders

There are two types of gluten intolerance-related disorders:⁴

• Autoimmune coeliac disease (CD)
• Non-coeliac gluten sensitivity (NCGS)

Coeliac disease (CD)

Coeliac disease is an autoimmune reaction to the gluten protein that damages the small intestine.⁸

Many genetic and environmental factors can contribute to its development. In general, CD most commonly occurs in genetically predisposed people (i.e., someone with a family history of coeliac disease).^9,10

CD presents with digestive symptoms (see “shared symptoms” section) similar to IBS and sometimes extra-digestive symptoms (e.g., anaemia, osteoporosis). However, some cases are silent/asymptomatic meaning they do not show obvious symptoms.⁹

Mechanism

For individuals with CD, their immune system mistakenly attacks and damages the healthy tissue of the small intestine. This is because it mistakes gluten as a threat to the body’s health. Therefore, gluten consumption may create a leaky gut environment through which food particles and microbes enter, causing inflammation and worsening the autoimmune attack on the intestines. This is what causes CD symptoms.¹

Diagnosis and treatment

The following are ways to test for CD:

• Blood tests to detect antibodies typical of CD
• Biopsy to confirm the diagnosis

The CD is treated with a gluten-free diet.

Non-coeliac gluten sensitivity (NCGS)

Although NCGS has an immune-related background, it is not an autoimmune disorder. It can only be diagnosed when you do not fulfil the criteria for CD or gluten allergy.⁸

Mechanism

NCGS presents with classic IBS symptoms in relation to wheat-related foods. Currently, there is insufficient evidence to suggest that a gluten-free diet reduces symptoms in NCGS; this indicates that gluten is not the primary cause. Instead, studies have found sensitivity to fructan (a sugar found in wheat) or gliadin (a protein found in wheat) in NCGS.^2,11 These molecules create a leaky gut environment, resulting in the same symptoms as CD.

Diagnosis and treatment

Presently, no reliable biomarkers or diagnostic tests for NCGS have been identified despite NCGS patients reporting symptoms related to eating gluten. The condition remains a diagnosis based on excluding CD and gluten allergy.⁸ No treatment has yet been found for NCGS.¹²

Future research in the gut-immune connection

Microbiome research

Current research is focused on figuring out how to manipulate the gut microbiome to treat food intolerance (e.g., gluten in coeliac disease) to reduce symptoms and help prevent the development of food intolerance and gastrointestinal autoimmune disorders.¹³

Nutritional management

In terms of nutritional management, researchers seek to better understand what molecules within foods cause reactions and potentially genetically modify them to prevent symptoms, such as with gluten-free flour.¹¹

Summary

Conditions such as coeliac disease and non-coeliac gluten sensitivity are caused or worsened by food intolerances. Certain foods induce a leaky gut, where partially digested food particles, toxins, and microbes can move through the intestinal wall barrier, resulting in symptoms affecting the digestive system and possibly the rest of the body. 

Restoring the gut microflora and fixing leaky guts could be key to resolving food intolerances and effectively treating food-related autoimmune conditions.

If you suspect you may have a food intolerance, an autoimmune disorder, or a gastrointestinal condition, please seek the advice of a GP or a dietitian.