How to keep the intestine healthy

Last updated on November 27, 2023 First published on November 03, 2023

A balanced diet and sufficient exercise keep the digestive organ fit. Screening can massively reduce the risk of colorectal cancer.

Text: Helga Kessler

It is a strange organ: a five to six meter long thin tube with many folds and villi is followed by an approximately one meter long, thicker section. A muscle seals the whole thing gas-tight. At first glance, the site of digestion seems very simple, but it is extremely complex: In the intestine, not only are nutrients broken down and absorbed, but pathogens are also warded off, hormones are secreted, and enzymes and vitamins are produced. “If everything functions smoothly, the intestine is healthy,” says lead physician Michael Scharl of the Department of Gastroenterology and Hepatology. For the intestine to remain healthy, the intestinal mucosa, which covers an estimated 40 square meters, and the microbiome, which consists of trillions of bacteria, must interact perfectly.

Training for the immune system

The mucous membrane is both a barrier and a place of exchange: on the one hand, it prevents microorganisms from spreading throughout the body; on the other hand, it is in contact with them, thus training the immune system. “The more different types of bacteria it has, the better,” Michael Scharl knows. In the small intestine, the mucosa secretes digestive enzymes and absorbs nutrients; in the large intestine, it recovers water. Glandular cells produce the mucus that allows food pulp and stool to slide easily. Blood vessels under the mucosa, together with lymphatic vessels, transport digested nutrients away. Millions of nerve cells regulate the activity of the intestinal muscles, control blood flow and the release of hormones, largely independently of the brain.

If the nerve regulation in the intestine is disturbed, this becomes noticeable in the form of abdominal pain, for example in irritable bowel syndrome. Physical well-being is closely linked to the bacterial colonization in the intestine. Around two kilograms of microorganisms are found mainly in the large intestine. As a quasi quid pro quo for accommodation, bacteria of the intestinal microbiome contribute, for example, to the synthesis of the happiness hormone serotonin or the sleep hormone melatonin, as well as to the synthesis of vitamins E, B12 and folic acid. Intestinal bacteria are involved in the synthesis of bile acids, and they break down dietary fiber that humans could not otherwise absorb. They produce short-chain fatty acids from cellulose – these in turn serve as food for the very bacteria that eliminate pathogens and protect against inflammation.

Stool transplantation after infection

If certain bacteria spread at the expense of others, the sensitive system can become unbalanced. Infection with Clostridioides difficile is particularly feared, leading to severe and life-threatening diarrhea. If treatment with various antibiotics fails, the entire microbiome is replaced via stool transplantation. “We do the therapy about every other week,” Michael Scharl says. The stool and its bacterial composition provide gastroenterologists with important information, for example about the risk of colorectal cancer. Corresponding tests are already under development.

Michael Scharl tends to advise against over-the-counter tests that are supposed to provide information about possible risks via stool samples: “At the moment, you can still derive too few concrete consequences from them.” The gastroenterologist advises a healthy lifestyle with regular physical exercise and a varied diet. “A balanced diet with whole grains, legumes, vegetables and fruits, not too much sugar and little processed meat and preferably with fresh products is good,” says nutritionist/therapist Brigitte Baru. Dietary fiber, as found primarily in plant foods, promotes the growth of protective bacteria. However, the recommended 30 grams per day is difficult for most people to achieve, says Brigitte Baru. If you want to optimize your diet, it’s best not to do it overnight: “A change takes time, the intestines have to get used to the higher amount of dietary fiber.”

Microbiome consultation

Prof. Michael Scharl, a specialist in gastrointestinal diseases, conducts research on the microbiome and heads the new microbiome consultation at the USZ. Find out what the consultation is about and who the offer is aimed at.

More information

Colonoscopy from 50

If the intestinal flora becomes confused, disorders such as diarrhea or constipation occur. More serious is when the intestinal mucosa becomes inflamed and when it begins to proliferate. Initially benign polyps can develop into malignant tumors over time. “From the age of 50, one should undergo a first colonoscopy “, says Christoph Schlag, head of endoscopy. In the largest endoscopic center in Switzerland, approximately 2700 complete colonoscopies are performed annually.

Mirroring of partial sections (sigmoidoscopy for the last 40 cm, proctoscopy for rectum and anus) may be useful for control after tumor surgery or for treatment of hemorrhoids. For colorectal cancer screening, a complete mirror examination is always recommended. “In 30 out of 100 people, we find polyps that we can remove,” Christoph Schlag says. Unfortunately, not even one in three adults over 50 in the canton of Zurich takes advantage of the pension option. For any doubters, the gastroenterologist has good news: “Most people who have already had a colonoscopy say afterwards that it wasn’t that bad.”

Trip to the own cave system

A mild sedative and anesthetic allows the person to sleep nicely covered on the couch during the colonoscopy. The gastroenterologist carefully advances a thin and flexible tube about 1.5 meters long, the endoscope, to the beginning of the small intestine. Then the examiner begins the slow retraction of the endoscope. Light source and video camera at the top provide clear images on the monitor – if you are not sleeping but watching, you will experience an exciting excursion into your own cave system. If the gastroenterologist discovers a polyp, he or she removes it with a snare or forceps. The mucous membrane heals by itself. After about 30 minutes, everything is over. Time for a coffee.

More about colonoscopy


Michael Scharl, Prof. Dr. med.

Senior Attending Physician, Department of Gastroenterology and Hepatology

Tel. +41 44 255 85 48
Specialties: Immunotherapy-associated colitis, Colorectal carcinoma, Microbiome

Christoph Schlag, PD Dr. med.

Senior Attending Physician, Department of Gastroenterology and Hepatology

Tel. +41 44 255 85 48
Specialties: Diagnostic and interventional endoscopy (ERCP, EUS, EMR, ESD, POEM, STER), Eosinophilic esophagitis, Gastroenterological functional diagnostics