Overview

The term food intolerance is used to describe the condition in which certain foods or specific ingredients are more difficult to digest than they’re supposed to. It can vary from mild gastrointestinal discomfort to bloating, headaches and even a lot of pain.¹ It does not relate to the immune system which is why food intolerance is different from food allergies. Symptoms can be similar at first, but only the second, in acute situations, can evolve into anaphylaxis.² It is important to correctly assess an intolerance to improve quality of life and avoid putting the body under the stress of chronic inflammation.

Common types of food intolerance

• Lactose intolerance
• Gluten intolerance (non-celiac gluten sensitivity)
• Fructose intolerance
• Histamine intolerance
• Others (sulfite, salicylate intolerance)

Symptoms of food intolerance

• Gastrointestinal Symptoms: bloating, fullness, diarrhoea, constipation, excessive gas, belly pain 
• Non-gastrointestinal symptoms: headaches, fatigue, mood changes, skin reactions, nasal congestion, wheezing and other respiratory symptoms

Initial assessment and patient history

The diagnosis of food intolerance leans on exploratory work to proceed with treatment. Understanding not only the timing and duration of symptoms but also possible family-inherited intolerances or allergies and past medical conditions is valuable to building the patient’s medical history.    

Besides, a detailed dietary history can provide clues as to the causes of the problem. Symptom diaries and frequency questionnaires are frequently used to explore how and when intolerances manifest. The symptom diary depends on the patient’s efforts to keep track of what they’re eating so the health professional can identify patterns.³ Another tool that can be used in combination is the food frequency questionnaire, composed of a list of foods, it allows the patient to outline their eating habits regarding intake frequency and portions. Despite relying on the patient’s memory and consciousness, it is an inexpensive, easy way to approach the diagnosis.⁴

Diagnostic tests and procedures

Elimination diet 

A protocol in which the patient removes a food or a group of foods from their diet for a period of time and then reintroduces it. It is important to be monitored by a health professional to safely and more accurately decide what should be excluded, for how long and how to proceed and adjust the plan in case symptoms remain unaltered. During this eating plan, minimization or worsening of symptoms can indicate a correlation between what was eliminated and intolerance reaction.⁵

Breath tests

Breath tests can be indicated when there is suspicion of lactose or fructose intolerance. The patient ingests a preparation with a lactose or fructose base. These carbohydrates are usually absorbed in the small intestines, but, if the absorption is defective there will be traces of it in the patient’s breath. These results are not a full diagnosis, but an intolerance indication.⁶

Blood tests 

In the search for solutions to feeling constantly unwell after eating, people may come across the IgG test. It works by identifying increased levels of IgG when the body is exposed to a certain food, claiming it will enable food sensitivity diagnosis.⁷ IgG refers to the most common antibody found in human blood, it has variants and holds memory of components the person was once exposed to. In the case of testing for food intolerance, Observing IgG response to specific components is not that assertive in determining food intolerance, as it is normal for the body to release IgG in healthy situations, it can just be a signal that won’t mobilize a protection reaction from the immune system.⁸

Biopsy and endoscopy

Food intolerance assessment is based mainly on the patient's complaints and symptoms. Some cases can benefit from the support of biopsy or endoscopy. These procedures may be needed in more difficult diagnosis cases, aiming to reveal local inflammatory reactions in the gastrointestinal system, possible infections or structural flaws. Although invasive, these exams can show that the root of the problem is not just the ingestion of a certain food. This allows other approaches to be added to the treatment, like antibiotics, corticoids, etc.⁹

Genetic testing (for lactose intolerance)

Not being able to produce lactase, an enzyme that breaks down the milk sugar, and lactose, and enables its digestion, is a common type of food sensitivity among adults. Its roots might be genetic and so can be obtained through the analysis of a blood sample. The test can determine whether or not the patient presents specific gene parts responsible for lactase synthesis.¹⁰

Differential diagnosis

Differentiating from food allergies 

Symptoms from food intolerance and allergies can be, initially, similar and overlap, but the mechanisms and possible consequences are quite different. Unlike intolerances, an allergy reaction activates the immune system into protection mode, which means the body identifies a harmless substance as a threat, therefore, it must be dealt with. Sometimes, immune cells will deal with it at all costs and work to anaphylaxis, an exacerbated inflammatory response. When someone is allergic to a specific food, even ingesting just a tiny portion can trigger a reaction. For food intolerances, the more food is consumed, the more discomfort will be felt. Both conditions deeply affect quality of life, but allergies can be life-threatening.¹¹

Differentiating from gastrointestinal disorders 

Irritable bowel syndrome (IBS) 

Altered bowel movements, causing abdominal pain and discomfort, can be signs of irritable bowel syndrome (IBS). This chronic disorder affects the gastrointestinal system, where the cells are believed to present a defective communication with the brain.¹² It results in organs being highly sensitive, reactive and irritable, consequently, most people with IBS present food intolerance.¹³

Inflammatory bowel disease (IBD) 

Crohn's disease and ulcerative colitis fall under the term inflammatory bowel disease (IBD). They are mainly characterized by an inflammatory condition of the gastrointestinal tract and, long term, can damage the tissue.¹⁴ People who suffer from IBD and people who suffer from food intolerance are different populations that significantly overlap. The reasons are unknown and under investigation, it is not sure if food intolerance contributes to IBD or the other way around, but it is important to notice that, still, they are distinct conditions.¹⁵

Celiac disease

Celiac disease is an autoimmune condition that requires complete restriction of gluten ingestion. If the contact happens, an exacerbated reaction from the immune system attacks its body intestine. Uncontrolled celiac disease can lead to malabsorption of nutrients, structural damage to the gastrointestinal system, diabetes, intestinal cancer, and more. Treatment consists of banning gluten from the diet. Celiac disease can not be defined as a food intolerance, as it engages immune reaction, but does not lead to anaphylaxis and is not simply a food allergy either.¹⁶

Management and treatment

When living with food intolerance, the main focus is to be aware of what’s eaten and reduce or avoid identified ingredients that cause discomfort. Additional approaches to improve quality of life can be used, like enzyme supplements for lactose intolerants. By taking the encapsulated lactase they can provide the enzyme, enabling ingestion of dairy products from time to time. Medications like antacids and anti-diarrhea can help in managing the uncomfortable symptoms.¹⁷

In the last few decades, industrialized foods have been required to add to their labels warnings of the presence of ingredients that are commonly an issue for people with intolerances or allergies. Gluten, dairy, egg products, peanuts and more are usually declared in a noticeable way.³

Summary

Having a hard time with digestion can be a sign of food intolerance and should be investigated. From feeling discomfort to even skin rashes, food intolerance can significantly drop one’s quality of life. Other illnesses and conditions are usually mistaken for food intolerance and it is important to reach a differential diagnosis so proper treatment and management can be provided. Food allergies, for example, can present similar symptoms at first, but by engaging an immune reaction to certain foods, they are life-threatening. 

Some laboratory tests can be performed to come to a more accurate conclusion as to why the gastrointestinal system seems deregulated and might be irritated by specific ingredients, but it all begins and revolves around the patient being attentive to their eating habits, keeping track of what is being ingested and when they feel the unwanted reactions during the day. 

A food intolerance diagnosis can be a bother to deal with, but, with habit changes, adapting recipes and with the help of a few medications, it is possible.