Summary
Food intolerance is a reduced ability of the body to digest certain types of food or food components. While less dangerous than food allergy, it lowers the quality of life of many people around the world. Find out about its causes and management.
What Is Food Intolerance?
Food intolerance is a problem with digestion of certain foods, usually accompanied by an unpleasant physical reaction. [1] This may include abdominal pain, rash, vomiting, bloating, or diarrhea. The onset of such symptoms is usually within hours after eating the food, but could be up to days.
Studies show that approximately 3.6% of people have adverse reactions to food in their medical records. [2] This includes both food allergy and food intolerance, two commonly confused conditions. Here’s how to discern them:
Not mediated by immune system
Food intolerance, unlike food allergy, is not mediated by a hypersensitive reaction of the immune system. [3] Usually, the culprit is an insufficient enzyme that cannot effectively degrade a specific food molecule.
Longer onset of symptoms
With food intolerance, the symptoms occur gradually (in hours), while food allergy symptoms present almost immediately. This is also why the diagnosis of food intolerance is often so elusive - when symptoms occur hours (or days!) after eating, it is hard to link them with a specific food.
Not a life threat
Food intolerance is not life-threatening - as opposed to food allergy, which may result in anaphylaxis. The anaphylactic reaction is a medical emergency with rapid onset of symptoms such as rash, serious shortness of breath, vomiting and low blood pressure. In people with food allergy, this reaction can be triggered by trace amounts of food, while in food intolerance, this is virtually never the case. [4]
Diagnosis
The most common way to diagnose food intolerance is by elimination diet. First, you create a food diary, noting what food you ate at what time. Then, you link the symptoms with a particular food. The suspect food is excluded from the diet for 2-6 weeks [1] to see whether symptoms disappear or not. If they do, the food is reintroduced little by little. Often, people find that there is a certain amount of the food they can tolerate without any symptoms.
As for laboratory testing, measuring antibody levels is the standard for differential diagnostics of some conditions. To name a few, anti-gliadin antibodies are measured when suspecting celiac disease, and anti-lactalbumin antibodies are tested for in non-IgE mediated cow-milk allergy (both in IgG and IgA class). [3]
Another option is FOX (Food Xplorer), a testing kit for IgG antibodies against 286 food antigens. The results, however, are not diagnostic in themselves and must be carefully interpreted by your doctor. This is because increased levels of IgG antibodies may represent normal immunological response to food antigens. [5] In fact, increased IgG4 denote tolerance rather than hypersensitivity. [4]
The 8 Most Common Food Intolerances
1. Dairy
People whose symptoms occur after eating dairy products are very often lactose intolerant. In fact, the current estimates [6] suggest that 68% of people globally have some form of this condition.
Lactose is a sugar contained in milk. It is digested by the enzyme lactase in the gut, which enables its absorption into the blood. Lactose intolerant people produce insufficient amounts of this enzyme. Undigested lactose then draws a lot of water into the gut, causing diarrhea. As lactose passes further into the colon, it is fermented by the microbiome in a process producing gas. This is why people also experience bloating and flatulence. [4] All of these lactose intolerance symptoms are commonly accompanied by nausea.
As of now, there is no cure for lactose intolerance. However, symptoms can be controlled by a lactose-free diet. Patients are advised to avoid yogurt, milk, ice creams or soft cheeses.
2. Gluten
Gluten is an umbrella term for some proteins contained in wheat, barley and rye. [4] In some people, eating gluten-rich foods induces unpleasant symptoms, such as bloating, diarrhea or abdominal pain. These are, however, not always attributable to gluten intolerance itself. This is because there are three different gluten-related health conditions: gluten intolerance, wheat allergy and celiac disease. Since their symptoms and associated health risks differ, it is useful to be able to distinguish them.
Celiac disease
Celiac disease is an autoimmune condition. This means that one’s own immune system attacks the body's own cells. In untreated cases, celiac disease can cause serious damage to the intestinal mucous membrane.
This condition is based on the immune system’s hypersensitive reaction to gliadin, a protein found in gluten. [7] In other words, when gluten enters the gut, inflammation occurs. In the short term, this presents as bloating, diarrhea and nausea. In the long term, however, severe damage to the intestinal cells occurs. That’s why it is so important for these patients to avoid eating gluten altogether.
At the level of genetics, there are two alleles that predispose for celiac disease: HLA-DQ2, HLA-DQ8. [4] Both of these are looked for when diagnosing celiac disease.
Another important diagnostic test for celiac disease is the measuring of various antibody levels. Specifically, these include anti-TG (transglutaminase), anti-DGP (gliadin fragments), as well as anti-EMA (endomysium) in classes IgG and IgA. [7]
Wheat allergy
Wheat allergy is also mediated by the immune system. In this case, however, antibodies (IgE class) are produced against some of the proteins in wheat, but not necessarily gluten. [4]
Wheat allergy is characterized by a rapid onset of nausea, hives or rash after eating food containing wheat. Swelling and itching of the mouth and throat are other very common symptoms. In severe cases, wheat allergy can be life-threatening in the form of an anaphylactic reaction (with symptoms such as breathing difficulties or fainting). This requires immediate medical attention.
Wheat allergy can be diagnosed just like any other food allergy, by skin-prick tests and elimination diets.
Gluten intolerance
There are also people who experience unpleasant symptoms, but show no signs of celiac disease or wheat allergy in their laboratory and clinical tests. These are often, by exclusion, diagnosed with gluten intolerance (a.k.a. non-celiac gluten sensitivity). [8]
Gluten sensitivity symptoms include: [9]
- bloating
- diarrhea
- abdominal pain
- rash
- headaches and fatigue
- depression
Management
The management of gluten intolerance, wheat allergy, as well as celiac disease is a gluten-free diet. [1] Patients need to avoid gluten-containing food, such as bread, pasta, beer, cereals or soy sauce.
3. Caffeine
Caffeine is a molecule found in coffee, tea, cola, and energy drinks. It increases alertness and attention, while decreasing drowsiness. For this reason, it is referred to as a stimulant.
Caffeine acts by blocking adenosine receptors, which are found in the central nervous system, heart, or the colon. In our brains, adenosine is a sleep-inducing molecule. That’s why caffeine decreases drowsiness by blocking its effects. [10] Adenosine also lowers heart frequency. [11] Drinking caffeine-rich beverages, therefore, has the inverse effect of increasing the heart frequency. Interestingly, adenosine also regulates the motor activity of the colon. [12] This may also explain why many people report that even just a sip of coffee makes them want to go to the toilet immediately.
In sensitive people, all of these effects may be amplified to the point when they become very unpleasant. Alertness turns to anxiety or insomnia, increased heart frequency becomes dangerously rapid heartbeat, and the urge to defecate reaches the level of diarrhea. Many also complain of heartburn. [12]
The basis of caffeine hypersensitivity is genetic, to an extent (a variation in adenosine receptors). [10] Another important factor is the variation in the enzymes that metabolize caffeine.
People with caffeine hypersensitivity should avoid drinking caffeine-rich beverages such as coffee, tea, cola, or energy drinks.
