What is a food intolerance?
The term food intolerance describes physical reactions to certain foods or food components without the involvement of the immune system in the production of specific antibodies, as is the case with a classic allergy. Instead, the underlying cause is usually an enzyme deficiency, a disrupted transport mechanism in the gut or a hypersensitivity to certain substances.
The symptoms can be non-specific and extend beyond the gastrointestinal tract. This is precisely why distinguishing them from other conditions is often challenging and requires careful evaluation.
Allergy or intolerance – what is the difference?
Even though the terms are often used interchangeably in everyday life, they describe different mechanisms:
- Food allergy: The immune system reacts to certain protein components in food, usually via IgE antibodies. Symptoms often occur after even the smallest amounts and can range from skin rashes to anaphylactic shock.
- Food intolerance: Here the immune system is not involved, or only indirectly. The symptoms usually depend on the amount consumed and often develop with a time delay.
- Pseudoallergy: A special form in which allergy-like symptoms occur without specific antibodies being detectable.
The most common forms at a glance
Three intolerances are particularly common in everyday practice: lactose intolerance, fructose malabsorption and histamine intolerance.
Lactose intolerance
Lactose is the natural sugar found in milk and dairy products. For the body to process it, it must be broken down into its components in the small intestine by the enzyme lactase. If lactase activity is reduced, undigested lactose passes into the large intestine, where it is fermented by bacteria.
Typical symptoms after consuming foods containing lactose:
- Bloating and a feeling of fullness
- Abdominal cramps
- Diarrhoea, sometimes also constipation
- Nausea
The severity varies considerably from person to person. Many of those affected tolerate small amounts – for example in mature cheese – without any problems.
Fructose malabsorption
In fructose malabsorption, the absorption of fruit sugar (fructose) from the small intestine into the bloodstream is impaired. The GLUT-5 transporter does not work sufficiently, so fructose enters deeper sections of the intestine where it can trigger symptoms similar to those of lactose intolerance.
Common symptoms include:
- Bloating and abdominal pain
- Diarrhoea or soft stools
- Tiredness and difficulty concentrating
- Mood swings, which are linked to a disturbed tryptophan metabolism
Important: Fructose malabsorption should not be confused with the rare, congenital hereditary fructose intolerance, which involves an enzyme defect in the liver and requires close medical supervision.
Fructose is found not only in fruit but also in many processed foods, juices and in the form of sorbitol in sugar-free sweets – sorbitol can further aggravate the symptoms.
Histamine intolerance
Histamine is a messenger substance produced by the body that is also present in many foods – particularly in mature, fermented or long-stored products such as hard cheese, red wine, salami, sauerkraut or tuna. In histamine intolerance, there is an imbalance between the histamine ingested and its breakdown by the enzyme diamine oxidase (DAO).
Typical symptoms of histamine intolerance:
- Skin redness ("flushing"), itching, hives
- Headaches or migraine-like symptoms
- Digestive complaints such as diarrhoea and abdominal pain
- A blocked or runny nose, swollen mucous membranes
- Palpitations, circulatory reactions
Since histamine influences many bodily systems, the clinical picture is often varied – which can make diagnosis more difficult. Stress, hormonal fluctuations and certain medications can also affect histamine metabolism.
Diagnostic steps in practice
A thorough investigation is important so as not to prematurely avoid entire food groups and thereby risk an unbalanced diet. Several tools are available in nutritional medicine practice.
Medical history and food diary
The starting point is a detailed conversation. What symptoms occur, how long after the meal and how often? A food and symptom diary kept over several weeks can provide valuable clues to possible triggers.
Breath tests
H2 breath tests have become established for lactose and fructose. After ingestion of a defined sugar solution, the hydrogen content in the exhaled air is measured. Elevated values indicate bacterial fermentation in the large intestine and therefore impaired processing.
Blood tests
- If an allergy is suspected, specific IgE antibodies can be measured.
- If histamine intolerance is suspected, the activity of diamine oxidase (DAO) in the blood is often measured. The diagnostic value of this measurement is assessed differently, however, and should always be interpreted in the context of the symptoms.
Elimination and provocation diet
A structured stepwise approach has proven particularly useful when histamine intolerance is suspected: after a phase with reduced histamine intake, potentially triggering foods are reintroduced in a targeted manner to test individual tolerance. This procedure should be supervised by a doctor or nutritional medicine specialist.
Distinction from other conditions
Symptoms such as bloating, diarrhoea or abdominal pain can also be caused by other conditions – such as irritable bowel syndrome, chronic inflammatory bowel disease, coeliac disease or a Helicobacter pylori infection. A comprehensive evaluation rules out these differential diagnoses.
What those affected can do themselves
Although the final diagnosis belongs in the hands of a doctor, some steps can make the path there easier:
- Observe rather than eliminate: A food diary is more helpful than independently leaving out many foods.
- Read labels: Lactose, fructose and sorbitol are often hidden in processed foods.
- Plan meals consciously: Fresh, minimally processed dishes are usually better tolerated than long-stored or fermented products.
- Be patient: The individual tolerance threshold can often only be assessed after a few weeks.
Conclusion
Food intolerances such as lactose intolerance, fructose malabsorption or histamine intolerance are a common cause of unclear symptoms – but they can also be diagnosed reliably. What matters is a structured investigation that clearly distinguishes allergies and other conditions and takes individual tolerance thresholds into account. This helps to avoid unnecessarily restrictive diets and can improve quality of life in a targeted way.
This article does not replace medical advice.