Colorectal cancer (CRC) is the second leading cause of cancer deaths —after lung cancer —worldwide. The World Health Organization reported 1,930,000 new cases and 935,000 deaths in 2020.
In the United States, early detection and prevention have contributed to rapid decreases in CRC incidence and mortality in the last 20 years. Reductions are thought to reflect the rapid dissemination of colonoscopy screening, which has a larger capacity for cancer prevention than other tests such as sigmoidoscopy, guaiac-based fecal occult blood testing, and fecal immunochemical tests.
Bowel prep changes microbiota
Colonoscopy is the gold standard for finding and removing polyps, which may develop into CRC. Prepping for the procedure requires imbibing liters of laxative solutions to cleanse (via diarrhea) the bowel for better viewing. Not a pleasant experience, but it’s a necessary step so that the physician can see a clear picture.
How do diarrheal agents—usually sodium phosphate or polyethylene glycol—affect gut microbes?
Several studies have addressed this.
- In an early study, changes in the fecal microbiota were examined in five individuals undergoing screening colonoscopy. In three of the five subjects, microbial profiles were different in stool samples collected after colonoscopy compared to stool collected before colonoscopy; bowel preparations changed the fecal bacteria.
- Another small study examined 12 healthy individuals, divided into three groups. All groups underwent baseline un-prepped flexible sigmoidoscopies (FSIG) with biopsies. The experimental group received a standard bowel cleanser, with control groups receiving none. After 12 post sigmoidoscopies, results showed that bowel preparation altered the diversity of mucosa-associated microbiota. Taxonomic classification did not reveal changes at the phylum level, but there were differences at the genus level.
- In a study of 20 overweight men, researchers found that the relative abundance of the most dominant bacteria hardly changed from prior to bowel preparation to 28 days after colonoscopy. However, depending upon the fecal type, the microbial diversity differed significantly after bowel preparation.
- A randomized control trial with 23 healthy subjects reported an instant and substantial change in gut microbiota after bowel cleanse.
In spite of using only a small number of subjects, these studies show that the human gut microbiota changes significantly following bowel prep for colonoscopy. The duration of these changes has also been studied.
Persistence of changes from bowel prep?
- In fifteen subjects undergoing bowel cleanse, short-term changes in fecal microbiota were observed but there was no lasting effect on the majority of subjects.
- The study of 23 subjects described prior did indeed find that although the composition of the microbiota was affected immediately after lavage, the unique composition and total bacterial load returned to baseline levels after 14 days.
- This quick recovery was confirmed in a 2019 study, which examined 70 fecal samples (24 in the bowel prep group and 46 in the control group). Additionally, 32 metabolites were significantly changed before and immediately after the prep, but these metabolites also recovered within 14 days.
- Conversely, a long-lasting effect was seen in fecal samples of 10 patients one month after bowel cleanse. Microbiota composition changed with a decrease in the Lactobacillaceae abundance, a beneficial bacterial family.
Microbiota and Complications
The microbiota may be implicated in several complications of bowel prep and colonoscopy.
In ulcerative colitis patients, colonoscopy is associated with an exacerbation of symptoms. Immediate changes in beneficial microbes may contribute to this phenomenon.
There is evidence suggesting that undergoing a colonoscopy predisposes patients to appendicitis within one week. The risk is low but any links to microbial change are worthwhile exploring.
Potential for Probiotics and Prebiotics
A probiotic preparation containing strains of Bifidobacterium infantis, Lactobacillus acidophilus, Enterococcus faecalis, and Bacillus cereus appeared beneficial in restoring intestinal microbial diversity as well as sharply reducing the abundance of pathogens, in a small 2020 clinical study.
Another probiotic mixture containing strains of Lactobacillus plantarum Lactobacillus lactis subspecies cremoris and Lactobacillus delbrueckiidiminished the presence and the severity of intestinal symptoms and improved stool form when given to a large outpatient group for 4 weeks after colonoscopy.
In addition, the duration of pain days post-colonoscopy was reduced in 133 patients taking a probiotic compared with 126 taking a placebo in one study. No significant effect was seen in terms of return to normal bowel function or bloating post colonoscopy. The probiotic capsule contained strains of Lactobacillus acidophilus and Bifidobacterium lactis.
Further, there is some indication that probiotics may benefit patients with irritable bowel syndrome who experience negative symptoms after bowel prep and colonoscopy. The mixture used in the trial contained strains of Lactobacillus casei, Lactobacillus acidophilus, Lactobacillus rhamnosus, Lactobacillus bulgaricus, Bifidobacterium breve, Bifidobacterium longum, and Streptococcus thermophilus combined with 250 mg prebiotic fructooligosaccharides . After 6 months of treatment, the effect of probiotics in patients who immediately used them after colonoscopy was more visible and more stable.
Butyrate-producing organisms are known to be depleted in inflammatory bowel diseases (IBDs) which can require serial colonoscopies. Selective prebiotic intervention may increase the relative abundance of butyrate-producing microbes before and after the colonoscopy. Thus prebiotic treatment may help reduce post-colonoscopy symptoms and hasten the return to a balanced microbiota in IBD patients.
As colonoscopies became commonplace, researchers focused on the effect of the required bowel cleanse on the gut microbiota. Evidence shows that the gut microbiota changes significantly following bowel prep for colonoscopy. While there is some conflicting data, long-term changes are not generally seen.
Still, there may be risks to even short-term changes and discomfort. Several studies show that probiotic supplementation may benefit those undergoing bowel prep and colonoscopy.
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