Tsunami in the Gut
Every year, around 1.5-2 million people in Germany undergo a colonoscopy. The doctor uses an endoscope to examine the bowel for changes. The prerequisite for this is a thorough bowel cleansing. But how does this drastic rinsing affect the microbiome, what are the risks and what can be done to ensure that the complex interplay of microorganisms is not permanently disrupted?
60,000 cases of bowel cancer per year
Every year, around 60,000 people in Germany and around 150,000 people in the USA are diagnosed with bowel cancer. The later malignant cells in the bowel are detected, the lower the cure and survival rates. While more than 80-90% of patients diagnosed at an early stage are still alive five years later, the 5-year survival rate drops to around 10-15% with advanced disease. For this reason, a colonoscopy is generally recommended from the age of 50 at the latest and repeated every 5-10 years. Intestinal flora and bowel cleansing play a decisive role in preparing for such an examination. Although alternative examination methods (such as immunological stool tests or virtual colonoscopies) exist and there are minor risks (such as intestinal perforation or bleeding), colonoscopy is considered the gold standard worldwide.
How does a colon cleanse work?
Before a colonoscopy, the bowel must be completely emptied to allow the gastroenterologist a clear view of the intestinal mucosa. In addition to a change in diet 3-5 days beforehand, the day before or, in the case of an examination in the late afternoon, on the same day, a bowel cleansing with special laxatives is used. PEG (polyethylene glycol)-based solutions, which produce an osmotic effect in the bowel, are most commonly used. PEG is a long-chain polymer that is not absorbed by the intestine and therefore binds water. This leads to a strong dilution and liquefaction of the intestinal contents. The electrolytes contained in the PEG solutions prevent a significant loss of minerals. The high volume of liquid triggers a strong flushing effect and the intestinal movement (peristalsis) thoroughly cleanses the bowel with several watery bowel movements.
Is the intestinal flora damaged during colon cleansing?
Even if side effects rarely occur, especially in people with heart or kidney disease, the question arises as to what effects this radical bowel cleansing has on the microbiome. After all, if the entire stool residue is flushed out of the intestine, aren’t the good bacteria also forcibly removed from the intestine, so to speak?
The answer is clear: yes, the microbiome is sensitively affected. However, it should be noted that only the intestinal microbiome is affected. All other human microbiomes, on the skin, in the stomach, in the mouth and actually everywhere on and in the body are not affected, but the effect of colon cleansing remains limited solely to the intestine.
How does the intestinal flora change during colon cleansing?
Taking the laxative solution leads to a massive reduction in the amount of bacteria in the intestine. Studies show that immediately after colon cleansing, the total number of intestinal flora decreases by orders of magnitude – in one study by around 31 times. As a result, part of the individual composition (the “fingerprint-like” specificity) of the microbiome is temporarily lost. Useful bacteria are greatly reduced, while at the same time relatively resistant germs or germs close to the mucosa can remain disproportionately or multiply temporarily.
Decrease in diversity after bowel cleansing
The effects are comparable to severe diarrhea. The general diversity of the intestinal flora decreases, while some bacteria may increase in the short term. This is also the case with cholera, for example. Here the causative agent of cholera, Vibrio cholerae, can offer resistance to the strong intestinal movements caused by its own toxins due to its strong mobility. While other germs are washed out, it remains in the intestine and can thus secure a growth advantage.
The initial state of the microbiome also plays a role in the effects of colon cleansing. Some microbiomes are more susceptible to loss of diversity during a gut cleanse than others. This means that the composition of the microbiome after colon cleansing varies depending on the initial situation. A healthy microbiome therefore also offers considerable advantages here.
Oxygen also damages intestinal bacteria
Another factor is oxygen, which can be introduced into the bowel during the colonoscopy: Intestinal germs generally do not tolerate oxygen. They can also be damaged if room air is used. This is why carbon dioxide (CO₂) is used nowadays, which is better tolerated, escapes more quickly and reduces flatulence.
Rapid regeneration of the intestinal flora after colon cleansing
Despite this drastic method, the intestinal microbiome has a remarkable ability to regenerate. The original state is usually restored within 2-4 weeks, after 6 weeks the intestinal flora is almost completely regenerated. Nevertheless, in rare cases individual populations can remain permanently damaged, especially if there was already an imbalance beforehand.
Why does the intestinal flora recover so quickly?
But why is the gut microbiome so resilient? In contrast to antibiotics, intestinal cleansing does not kill the bacteria, but merely flushes them out. However, individual representatives can escape the turbulence in intestinal protrusions or other niches. As soon as the intestinal cleansing is over, they can multiply again as long as no pathogenic germs dominate. The original intestinal microbiome can thus be restored in a relatively short time.
Practical tips to support the intestinal flora after a colon cleanse
How can the gut microbiome be supported after a colon cleanse?
1. split-dose scheme
The laxative solution is divided into two separate doses. The microbiome is less disturbed in this way than if the entire dose is taken at once. This is why the split-dose scheme is preferred nowadays.
2. targeted use of probiotics
The use of probiotics after colon cleansing with subsequent colonoscopy helps to mitigate the microbiome changes by restoring certain bacterial genera more quickly. However, the timing of the intake is crucial: the probiotics should be taken immediately after the colonoscopy – the sooner, the better. The composition of the individual probiotic preparations is also crucial, as they serve as a “boost” for the restoration of the intestinal flora. If the probiotics do not contain some of the bacteria that were originally present in the intestinal flora, regeneration cannot be accelerated. As each intestinal microbiome is individual, ideally the composition of the most important bacteria groups should be analyzed before the intestinal cleansing and these should then be specifically added again with a probiotic. Although this personalization is the best way, it is rarely practiced.
3. nutrition
As described above, the bacteria are not wiped out as with an antibiotic atom bomb, but still exist in the intestine, albeit in small quantities. It is therefore important to support them again immediately after the colonoscopy, preferably with fiber, which only these microorganisms can process. This is best done with a plant-rich and fiber-rich diet or by administering special prebiotics such as inulin. Fermented foods such as yoghurts, kefir, sauerkraut or kimchi also provide beneficial microorganisms and can support recolonization. It is important to give the intestines time to recover: Immediately after the colonoscopy, you should start with a light diet and then switch to whole foods rich in probiotics and prebiotics to promote the growth of healthy intestinal flora.
No permanent damage from bowel cleansing
Colon cleansing before a colonoscopy does not usually cause any permanent damage. Although the microbiome may be severely disrupted in the short term, it regenerates quickly. However, it would be problematic if an antibiotic were administered immediately after a bowel cleansing, as these two effects can negatively reinforce each other.
Normally, however, the intestinal microbiome can regenerate quickly and reliably with the right support. (JS)
Further reading
Jalanka J. et al. (2015): Effects of bowel cleansing on the intestinal microbiota. Gut 64(10):1562-1568. DOI: 10.1136/gutjnl-2014-307240
Drago L. et al. (2016): Persisting changes of intestinal microbiota after bowel lavage and colonoscopy. Eur J Gastroenterol Hepatol 28(5):532-537. DOI: 10.1097/MEG.0000000000000581
Jo H.H. et al. (2023): Alteration in gut microbiota after colonoscopy: proposed mechanisms and the role of probiotic interventions. Clinical Endoscopy 56(3):239-249. DOI: 10.5946/ce.2022.158
Labenz J. et al. (2023): Application of a multispecies probiotic reduces gastrointestinal discomfort and induces microbial changes after colonoscopy. Front Oncol 12:1078315. DOI: 10.3389/fonc.2022.1078315
Son D. et al. (2023): Benefits of Probiotic Pretreatment on the Gut Microbiota and Minor Complications after Bowel Preparation for Colonoscopy. Nutrients 15(5):1141. DOI: 10.3390/nu15051141
Tseng C.H. et al (2019): Gut microbiome changes in overweight male adults following bowel preparation. BMC Genomics 19(Suppl 10):904. DOI: 10.1186/s12864-018-5285-6
