Have you noticed that you often feel bloated or experience indigestion after eating certain foods? Do you suspect that your body is intolerant to some food items? If so, you might be dealing with food intolerance. Food intolerance is the difficulty in digesting certain food items or ingredients. Observing the signs and symptoms and eliminating foods that cause intolerance is the key strategy for managing food intolerance.

In the last twenty years, the number of cases reported in the western population as adverse reactions to food has increased to 20-35%.  These adverse reactions can be due to either food intolerances or food allergies. According to an expert panel sponsored by the National Institute of Allergy and Infectious Diseases (NIAID), food intolerance is defined as “nonimmune reactions that include metabolic, toxic, pharmacologic, and undefined mechanisms”. In contrast, food allergy is “an adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food.”¹ 

Even a small amount of allergenic food may trigger severe reactions that could be fatal in those with food allergies. In contrast, food intolerance results in less severe symptoms. While it's not life-threatening, understanding food intolerance is important as it may affect the quality of life of the individual.

Understanding food intolerance

The term food intolerance can encompass a range of food-related symptoms of various causes. Most of the cases of food intolerance are self-reported and are not based on validated tests. The causes of food intolerance can include poor absorption and fermentation by intestinal bacteria. Food intolerance can be categorised as functional or structural.

Functional food intolerance can be due to functional disorders like the enzyme lactase deficiency in the small intestine. Structural food intolerance can be due to diseases that cause structural alterations in the gastrointestinal tract. Small intestinal diverticula is one such condition that results in bacterial overgrowth in the small intestine, resulting in bloating and diarrhoea after eating.²

A recent study has reported that food intolerance is often associated with anxiety and depression, thereby reducing the quality of life.³

Common symptoms of food intolerance

Recognising food intolerance signs

Digestive issues

Chronic exposure to intolerant food may result in low-grade inflammation in the stomach. The symptoms may take several hours to appear and may last for several hours. It includes a feeling of fullness even after having just a small amount of food, diarrhoea, constipation, abdominal pain, flatulence, and bloating. Food intolerance is also common in those with irritable bowel syndrome, a digestive system disorder. It typically resolves once the intolerant food is avoided and returns once it is reintroduced.³

Skin reactions

A diet that includes high protein intake, excessive calories, and saturated fatty acids may trigger skin reactions like rashes, eczema, and acne in some individuals. These symptoms may take a while to appear and may last up to several days. 

Respiratory reactions

Studies show that there may be a correlation between common cold, nasal congestion, and symptoms like sinusitis with certain food items.⁴ When the symptoms are less severe, these may be classified as intolerance. However, if even a small quantity triggers severe reactions, the intolerant food should be considered as a potent allergen.

Neurological effects

Food intolerance can affect the nervous system when there is continuous and repeated exposure to the offending food. It can result in mood disorders, headaches, brain fog, migraines etc.

Common culprits of food intolerance

Lactose

Lactose intolerance is a common type of food intolerance seen in people who consume lactose, a kind of sugar found in milk and milk products. Usually, lactose is converted to glucose and galactose by the enzyme lactase in the small intestine. A deficiency of this enzyme results in lactose intolerance.

Lactase enzyme levels peak after birth and tend to decrease with age in humans. Symptoms are usually seen in adolescence or early adulthood. It includes bloating, diarrhoea, constipation, stomach pain, gas, nausea, vomiting, mouth ulcers, headache, lack of concentration, joint and muscle pain, eczema, and trouble urinating. Sometimes lactose intolerance is also associated with inflammatory disorders of the gastrointestinal system like Gastroenteritis, Coeliac disease, Crohn's disease or it may occur secondary to chemotherapy and improper usage of antibiotics.⁵

Gluten

Non-coeliac gluten sensitivity (NCGS) is a type of food intolerance caused by the consumption of gluten-containing food, but without the presence of coeliac disease or wheat allergy. Coeliac disease is an autoimmune disease where the immune system attacks the body, leading to gut damage when gluten is consumed. 

Gluten is a type of protein found in wheat, barley, and rye-based products. Gluten is normally broken down in the intestine by the enzyme protease, but in some people, when they are present in abundance, it is difficult to digest. The symptoms include bloating, diarrhoea, abdominal pain, nausea, headache, tiredness, joint pain, depression, blurred mind, dermatitis, and a general lack of well-being.⁶

Histamine

Histamine intolerance is caused due to the imbalance in the amount of histamine released from food and the body’s ability to digest it. It is caused mainly due to the deficiency of the enzyme DAO. The typical signs include skin manifestations like rashes on the body, flushing of the face, dermatitis, and swelling. Other symptoms include diarrhoea, vomiting, constipation, abdominal pain, low blood pressure, increased heart rate, nasal congestion, sneezing, headache, dizziness etc.⁷

Food items like aged cheese, vinegar, soya sauce, yoghourt, kombucha, bacon, salami, pepperoni, luncheon meats, hot dogs, dried fruits like apricots, prunes, dates, figs, raisins, alcoholic beverages–especially wine, champagne, and beer–may cause histamine intolerance. 

Other common intolerances

Fructose

Fructose is a simple sugar found in fruits, vegetables, and honey. Even though it's uncommon, some people may develop intolerance to fructose. Fructose intolerance can be of two types: hereditary fructose intolerance and dietary fructose intolerance.

Hereditary fructose intolerance is caused by a mutation in the enzyme aldolase B, responsible for the metabolism of fructose. Dietary fructose intolerance is due to the malabsorption of fructose in the intestine. The symptoms of hereditary fructose intolerance include nausea, vomiting, abdominal pain, stunted growth, jaundice, aversion to sweets, liver damage, kidney damage, seizures, organ failure, and coma.⁸ The symptoms of dietary fructose intolerance include bloating, abdominal pain, nausea, gas etc.⁹

FODMAPs

FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols) are types of carbohydrates that are difficult for the gut to absorb. A high FODMAP diet usually results in abdominal pain, diarrhoea, constipation, bloating, distention, tiredness, and flatulence in sensitive individuals.⁹ Most legumes, processed meat, apples, watermelons, and ripe bananas are some examples of high FODMAP foods, whereas plain-cooked meats, tofu, eggs, grapes, strawberries, and pineapples fall into the category of low FODMAP foods.

Food additives 

Food additives like MSG(Monosodium Glutamate) and sulfites can sometimes cause food intolerance and hypersensitivity. The reaction occurs soon or up to 12 hours after ingestion of the food. The symptoms include skin reactions like urticaria, angioedema, itching of the skin or other symptoms like flushing, hypotension, abdominal pain, deregulation of bowel movements, and tachycardia.¹⁰

Diagnosis of food intolerance

Elimination diet

An elimination diet involves eliminating suspected food items one by one and then reintroducing them into the diet after a period of time. This process helps identify which foods are causing intolerance.

Food diary 

Keeping a food diary can help you to identify intolerant foods. Record all the food that you eat and note down in the diary if any symptoms occur. Avoid the foods that cause the symptoms, and after a few days, reintroduce them and observe any effects.

Medical testing 

There are certain tests like blood tests and breath tests that can diagnose food intolerance. However, elimination diets are considered the gold standard for diagnosis.

Management strategies

Managing food intolerance includes identifying and avoiding the trigger foods and substituting them with alternatives. Always try to read the label before buying food products if you are intolerant to any food. Include plenty of probiotics in the diet which helps to improve gut bacteria which can aid in digestion. If you are intolerant to certain foods, practical tips like meal planning, especially while dining out and travelling, can help you cope with the situation. It is essential to listen to your body and seek medical help if necessary.

FAQs

How do you know if you have a food intolerance?

An elimination diet and keeping track of symptoms can help identify food intolerances. There are some blood tests and breath tests for specific intolerances like lactose. If you are having trouble identifying the intolerant food, a healthcare provider can assist in diagnosis.

What are the three most common food intolerances?

Lactose, gluten, and histamine intolerance are the most common types of food intolerances.

What happens if you keep eating food you're intolerant to?

You may experience symptoms like abdominal pain, diarrhoea, bloating, and headaches. Even though these symptoms are not life-threatening, they may affect your quality of life.

How quickly do food intolerance symptoms appear?

It may appear within half an hour to 48 hours after consuming the food in question.

Summary

Food intolerance generally causes symptoms like bloating, gas, diarrhoea, constipation, abdominal pain, rashes on the body, acne, itchy skin, nasal congestion, headaches, brain fog, tiredness etc. Recognising the signs and symptoms helps to diagnose food intolerance and helps in self-management. The most common triggers include lactose in dairy products, gluten in wheat and barley, histamine found in aged cheese, processed meat etc. Eliminating the suspected food, reintroducing it after a few weeks and observing the recurrence of symptoms helps in the diagnosis of food intolerance. If you suspect a food intolerance, substitute the intolerant food with alternatives, maintain healthy habits and consult healthcare providers if necessary.