Fasting has an impressively positive reputation in the medical world: fewer calories, lower insulin levels, less inflammation, and more autophagy. It sounds like a metabolic wellness break at the cellular level. But right where many traditional fasting regimens aim to be particularly thorough, problems arise: in so-called colon cleansing.
Bear in mind: The gut is not a drainpipe, but an ecosystem. And anyone who “cleanses” this ecosystem with Glauber’s salt, Epsom salt, enemas, or colon hydrotherapy isn’t just getting rid of supposed waste—they’re also disrupting the microbial infrastructure that’s essential for health, immune modulation, and metabolism.
The Underestimated Player in Metabolism
Short-chain fatty acids, vitamins, antioxidants, and anti-inflammatory substances—the intestinal microbiome produces all of these. Butyrate, in particular, is considered a metabolically interesting candidate: it stabilizes the intestinal barrier, has anti-inflammatory effects, and is associated with beneficial effects on body weight.
A diverse microbiome is thus not merely a decorative accessory to a healthy diet, but an important functional player. Fasting can have a beneficial effect on the microbiome. Studies suggest that intermittent fasting and fasting periods lasting several days can increase microbial diversity and promote beneficial bacteria. However, what happens during the eating windows is crucial: Combining intermittent fasting with a low-fiber diet quickly undermines the concept.
Colon Cleansing: An Old Tradition, a Newly Recognized Problem
Many classic fasting protocols are from a time when the microbiome was not considered scientifically significant. Nowadays, some aspects of these protocols seem outdated. A study on the ten-day Buchinger fasting regimen—which traditionally begins with a bowel cleansing—shows where this can lead: pro-inflammatory proteobacteria increased, while important fiber-metabolizing bacteria such as Ruminococcaceae decreased, an effect that only returns to normal after about three months (Mesnage et al. 2019). Since fasting and bowel cleansing are inextricably linked in the Buchinger protocol, the study leaves open which of the two factors was actually the driving force—one more reason to at least skip the bowel cleansing as a precaution. A bowel cleanse isn’t effective as a “detox” anyway: detoxification is the job of the liver, the kidneys—and also an intact microbiome.
A large British biobank analysis involving over 500,000 participants suggests that this is not only unpleasant in the short term but may also have long-term implications: Those who regularly took osmotic laxatives such as Glauber’s salt or Epsom salt had a significantly increased risk of dementia (Yang et al. 2023, Neurology). Whether the laxatives are the direct cause remains unclear—but it’s one more reason not to voluntarily subject your gut to this procedure.
In practical terms, this means: fasting, yes; “slash-and-burn,” no. More sensible approaches include plant-based eating windows, prebiotic fiber, probiotics, and—contrary to old fasting folklore—coffee.In a large Dutch cohort study conducted by the University of Groningen, coffee—along with wine and tea—was among the beverages that most strongly promoted the diversity of gut bacteria (Zhernakova et al. 2016, Science). Your gut flora will likely be grateful.