Introduction

What is food intolerance?

Food intolerance refers to having difficulty in digesting certain food items or the ingredients present in them. It is primarily a digestive/gut issue, and is not the same as a food allergy. The digestive system in your body is incapable of digesting food due to either a deficiency in certain enzymes or sensitivity to the said food. It is usually not fatal,  but eating the food you're intolerant to can make you feel ill.

Is food intolerance and food allergy the same?

Often food intolerance and food allergy are confused to be the same thing but they differ fundamentally. Food allergy is caused by an adverse reaction of the immune system triggered by normally harmless food substances.¹ On the other hand, food intolerance is often subtle and not obvious, and harder to diagnose.²

Common types of food intolerances

Lactose intolerance

This is the most common type of food intolerance seen in people, and can occur at any age. It is caused due to a deficiency of an enzyme called lactase,  which breaks down lactose. Lactose is a kind of sugar found in milk and other dairy products. Lactose intolerance differs from a milk allergy, as the latter involves the immune system. Symptoms of a milk allergy are also different, involving, but not limited to itching and swelling. Lactose intolerance can be the consequence of some health conditions, including the following:

• Bowel infections
• Crohn’s disease
• Treatments such as radiotherapy, certain medications, or surgery ³

Gluten intolerance (Non-celiac gluten sensitivity)

Gluten intolerance is caused when the body has difficulty digesting gluten, a kind of protein found in wheat, rye, barley and related grains. Gluten intolerance is not the same as coeliac disease, which is an autoimmune condition where gluten harms the small intestine. In non-celiac gluten sensitivity, your body finds it hard to digest gluten, which in turn causes various symptoms, making you feel unwell.⁴

Fructose intolerance

Fructose intolerance occurs when the small intestine cannot properly absorb fructose, a sugar naturally found in fruits, honey, and some vegetables. There are two types of fructose intolerance: dietary and hereditary.

In dietary fructose intolerance, your body cannot absorb fructose efficiently (malabsorption), hence causing uncomfortable symptoms. Whereas in hereditary fructose intolerance, you are genetically deficient in the enzyme that is responsible for digesting fructose.⁵

Histamine intolerance 

Histamine intolerance is caused when your body lacks the enzyme that digests histamine, a chemical found in certain foods such as:²

• Cheese 
• Avocados 
• Bananas 
• Pineapple 
• Sausages 
• Vinegar 
• Red wine 

Histamine is known to aggravate allergies and adverse reactions in the body.

Food additives

Common food additives fall under the following categories: 

• Preservatives: include nitrites/nitrates, which can be found in processed meats such as bacon and salami
• Flavour enhancers: include MSG (monosodium glutamate). MSG can be found in cured meats, ripened fruits and savoury foods 
• Emulsifiers: include soya lecithin
• Artificial colours: include carmine, annatto and tartrazine
• Thickening and stabilising agents: include xanthan gum and carrageenan

Some people develop adverse reactions to these additives in food, which may cause various symptoms, such as itching and digestive symptoms, depending on the additive. No diagnostic tests presently can detect an intolerance to food additives.²  

Causes and risk factors

Genetic predisposition

Genetic predisposition means that some people are more likely to develop food intolerances because of their genes. If your parents or other close family members have food intolerances, you might have a higher chance of having them too.⁶

Enzyme deficiencies

• Enzyme deficiencies occur when your body doesn’t make enough of certain enzymes needed to digest specific foods. For example, people with lactose intolerance lack enough lactase enzyme to break down lactose, the sugar found in milk and other dairy products. This can lead to symptoms like bloating and diarrhoea when they consume dairy products⁶

Gut health and microbiome

Gut health and microbiome refers to the balance of bacteria and other microorganisms in your digestive system. A healthy gut microbiome helps in digesting food and keeps your digestive system functioning well. Antibiotics, poor diet, or illness cause imbalances which can lead to food intolerances.⁷

Symptoms of food intolerance 

The most common symptoms fall under the following categories:

Digestive issues 

• Bloating: It is a feeling of fullness or swelling in the abdomen
• Gas: Excessive burping or flatulence
• Diarrhoea: Frequent, loose, or watery stools
• Constipation: Difficulty in passing stools or infrequent bowel movements
• Abdominal pain: Usually, cramping or discomfort in the tummy
• Nausea: This is a sensation of uneasiness and discomfort in the stomach, sometimes leading to vomiting^{2, 8}

Headaches and migraines 

• Headaches: Persistent pain or discomfort in the head
• Migraines: Severe, throbbing headaches often accompanied by other symptoms including, but not limited to nausea and vomiting^{2, 8}

Fatigue

• General tiredness: Feeling unusually tired or weak, even after getting enough sleep
• Brain fog: Difficulty concentrating, thinking clearly, or remembering things⁸

Skin problems

• Rashes: Red, itchy, or inflamed patches on the skin
• Hives: Raised, itchy welts on the skin
• Eczema: This is a condition causing dry, itchy skin ²

Respiratory issues

• Nasal congestion: A stuffy or runny nose
• Asthma-like symptoms: Shortness of breath, sneezing, wheezing, or coughing²

It's important to understand that not everyone will experience all of these symptoms. Some of the symptoms occur in people who have a type of food intolerance, for instance, histamine intolerance causes certain respiratory and skin-related symptoms, whereas gluten intolerance causes digestive symptoms.^2,8 

Diagnosis of food intolerance

• Medical history: The healthcare provider will take a detailed medical history, including any known allergies, previous digestive issues, and family history of food intolerances or allergies. Patients are often asked to keep a detailed record of their symptoms, including what they eat and drink, the timing of symptoms, and their severity. This can help identify patterns and potential trigger foods⁹
• Elimination diet: This involves removing suspected foods from the diet for a period, typically 1-2 weeks. Common culprits like dairy, gluten, and high-fructose foods are often eliminated. Foods are reintroduced individually, with careful monitoring for the onset of any symptoms. This helps to establish a relationship between the symptoms and the said food substance⁹
• Breath tests: These tests measure the amount of certain gases like hydrogen in the breath after consuming specific sugars (e.g., lactose, fructose). High levels of these gases can indicate an intolerance⁹
  • Lactose breath test: Used to diagnose lactose intolerance
  • Fructose breath test: Used to diagnose fructose intolerance
• Blood tests: These can measure the body’s reaction to certain foods by checking for antibodies or other markers⁹
• Skin prick tests and blood IgE tests: While these are primarily used for diagnosing food allergies, they can help rule out an allergy as the cause of symptoms⁹

Management and treatment

You might need to adjust your diet to reduce or remove foods that cause issues. Many individuals with food intolerances discover that consuming small portions of problematic foods can minimise or prevent symptoms. If symptoms do arise, over-the-counter medications such as antacids or antidiarrheals can provide relief.

You might also think about trying substitutes for the food you are intolerant to. For example, lactose intolerant individuals may opt for substitutes such as dairy-free milk and other products. Similarly, gluten-free food items are available and all the rage in the market these days! 

Certain enzyme supplements are also sold at pharmacies to help digest food that you’re intolerant to. ² 

Summary

Food intolerance is a digestive issue where the body struggles to break down certain foods due to a lack of specific enzymes or sensitivity. Unlike food allergies, which trigger the immune system, food intolerances primarily cause digestive discomfort like bloating, gas, and diarrhoea.

Common food intolerances include lactose intolerance, gluten intolerance and fructose intolerance. Histamine intolerance and reactions to food additives like MSG are also prevalent. The causes of food intolerance can be due to genetics, enzyme deficiencies, poor gut health, age, and lifestyle factors. You may have several symptoms that can range from digestive issues to headaches, fatigue, skin problems, and respiratory issues.

Additionally, diagnosis can be made by your doctor by taking a medical history, keeping a food diary, elimination diets, breath tests, and sometimes blood tests. There may be no treatment for this but it can be managed by dietary adjustments to avoid trigger foods, using over-the-counter medications for symptom relief, and opting for food alternatives like lactose-free or gluten-free products. Enzyme supplements can also aid in digestion of specific foods.

FAQs

What is food intolerance? 

Food intolerance is when your body has trouble digesting certain foods, leading to discomfort like stomach pain, gas, or diarrhoea.

How is food intolerance different from a food allergy?

Food intolerance involves the digestive system and usually causes milder symptoms. Food allergies trigger the immune system and can cause severe reactions like swelling, hives, or anaphylaxis.

What are common symptoms of food intolerance? 

Symptoms include bloating, stomach cramps, gas, diarrhoea, and sometimes headaches or skin rashes. These usually appear a few hours after eating the problematic food.

How can I identify if I have a food intolerance? 

Keeping a food diary can help. Make a note of what you eat and any symptoms you notice afterwards. This can help identify patterns and pinpoint problem foods.

What are some common foods that cause intolerance? 

Common culprits include dairy products (lactose), wheat and gluten, certain fruits and vegetables (fructose), and food additives like artificial sweeteners or preservatives.

What should I do if I suspect I have a food intolerance? 

Consult with a doctor or dietitian. They may recommend an elimination diet, where you remove 

Can food intolerances be treated? 

While there's no cure, you can manage symptoms by avoiding or limiting the problem foods. Over-the-counter medications like antacids or antidiarrhoeals can help relieve symptoms when they occur.