When the intestine is irritated

Jul 30, 2025

The long road to diagnosis

Diarrhea, constipation, or alternating between both? Bloating, bloating, intestinal cramps? One in four adults suffers from irritable bowel syndrome. The intestines respond to stress, as well as food intake, with distressing and even painful symptoms. Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders. It affects an estimated 15–20% of the population and occurs primarily in adults, with women being affected more often than men. It is characterized by chronic complaints in the digestive tract that severely impair quality of life – but without organic causes such as inflammation or tumors, without allergies, and without food intolerances.

Irritable bowel symptoms: diverse and individual

The symptoms vary from person to person, but typical ones are:

• Cramp-like abdominal pain, often relieved by bowel movements
• Bloating and feeling of fullness
• Altered bowel habits: diarrhea (IBS-D), constipation (IBS-O), or alternating between both (IBS-M)
• Incomplete emptying after bowel movement

Additionally, fatigue, sleep disturbances, or psychological stress such as anxiety and nervousness may occur. A special feature: the symptoms never occur at night.

Diagnosis: Exclusion of other diseases

Since IBS doesn't cause structural changes, diagnosis is made by exclusion. Doctors use the so-called Rome IV criteria: Significant abdominal pain occurs at least once a week and lasts for more than three months, often in combination with diarrhea or constipation. In addition, blood tests, stool samples (e.g., for inflammatory markers), ultrasounds, or colonoscopies are performed to rule out conditions such as celiac disease, Crohn's disease, or intestinal infections. Those affected are also tested for food intolerances. Fructose, lactose, and histamine intolerance can trigger symptoms similar to those of irritable bowel syndrome.

If lactose cannot be digested

If the enzyme lactase is not available or only available in reduced quantities during digestion, lactose cannot be digested. Experts refer to this as lactose intolerance. This food intolerance causes symptoms similar to those of irritable bowel syndrome: bloating, diarrhea, abdominal cramps, and nausea. However, if symptoms occur 30 minutes to two hours after consuming dairy products, lactose intolerance is more likely. Diagnosis is made through a hydrogen breath test, a lactose tolerance test, or an elimination diet.

Eating fruit with negative consequences?

If bloating, diarrhea, and abdominal pain occur after consuming fructose-containing foods such as apples, honey, or soft drinks, fructose malabsorption may be present in addition to IBS. This means that the small intestine is unable to absorb fructose. Diagnosis is also made through a hydrogen breath test after consuming fructose.

No-Go: Cheese and red wine

Another food intolerance that is also associated with gastrointestinal problems is histamine intolerance. Histamine is a biogenic amine that acts as a messenger in the body (e.g., in allergies) and is found in foods (cheese – especially long-aged cheese like Parmesan, wine – especially red wine, fish – and reheated foods). The cause of the symptoms is an imbalance between histamine absorption (through food) and its breakdown by the enzyme diamine oxidase (DAO). Symptoms can include abdominal cramps, diarrhea, and vomiting, as well as skin reddening (often a veritable flash) and headaches. Diagnosis is made through a DAO enzyme activity test.

Diagnosis with obstacles

The fact is that diagnosing IBS is not easy. Many patients literally run from pillar to post – often several years pass – before receiving a definitive diagnosis. The reason: IBS is a functional disorder without a detectable organic cause. Intolerances and allergies, on the other hand, have clear triggers (e.g., lactose, fructose, histamine) and can be identified through testing. Therefore, if neither allergies nor intolerances are present, the treating physician will diagnose IBS by exclusion.

Scientific and medical literature sources (Germany & Austria):