Intermittent Fasting Temporarily Lowers Gut Butyrate, Then Diversity Rebounds: What the Research Shows

Intermittent Fasting Temporarily Lowers Gut Butyrate, Then Diversity Rebounds: What the Research Shows

Medical disclaimer: This article summarises published research for informational purposes only. It is not medical advice and is not a substitute for guidance from a qualified health professional. Always consult your doctor before starting any fasting protocol, especially if you have an existing health condition or take medication.

Study at a Glance

What This Study Looked At

Researchers wanted to know whether Ramadan fasting — a form of daily intermittent fasting practiced by observant Muslims for about a month each year — produces the same kind of gut microbiome shifts that shorter time-restricted eating windows are known to cause. Rather than measuring weight or blood sugar, this study tracked the gut microbiome directly, using stool samples to follow short-chain fatty acid (SCFA) levels — including acetate, propionate, and butyrate — before, during, and after the fasting month. These SCFAs are byproducts of gut bacteria fermenting fiber, and they matter because they feed colon cells, support the gut lining, and influence inflammation throughout the body. For more on how digestive rest fits into fasting more broadly, see why your digestive system needs a complete rest.

Who Was Studied

Participant profile: All 20 participants were adult Muslim volunteers who observed Ramadan fasting; detailed age range and gender split were not available in the accessible portions of the published abstract.

How the fasting protocol worked in this study: Participants ate nothing and drank nothing from dawn until sunset each day for roughly four weeks, consuming meals only during the overnight hours (suhoor before dawn, iftar after sunset) — the standard Ramadan pattern. Researchers collected fecal samples at baseline, during the fasting month, and again 4 weeks (PR4) and 8 weeks (PR8) after Ramadan ended, analyzing them for bacterial composition and SCFA concentrations by liquid chromatography-mass spectrometry.

What the Researchers Found

Short-chain fatty acids dropped during fasting, then recovered

• All three major SCFAs — acetate, propionate, and butyrate — showed a consistent downward trend throughout the fasting month, and this dip persisted for a month after Ramadan ended before recovering.
• The recovery wasn't immediate: it took roughly two months after the fasting period for SCFA levels to normalize.

Gut bacteria and SCFA levels were closely linked

• Levels of Lactobacillus, a genus known for fermenting fiber into SCFAs, correlated strongly with acetate (Rho = 0.64, p = 0.0024) and butyrate (Rho = 0.62, p = 0.0034) — meaning as Lactobacillus abundance changed, SCFA levels tended to move in the same direction.

Microbial diversity increased after fasting ended

• Overall gut microbial diversity was reported higher in the post-Ramadan period compared to during active fasting, suggesting the fasting month itself may temporarily narrow the range of bacterial species present.

What Did Not Change

• The study did not report any adverse safety events among participants during the fasting month.
• Broad bacterial phylum-level composition remained largely stable, with the more significant shifts occurring at the level of specific genera and SCFA output rather than wholesale restructuring of the microbiome.

What the Researchers Concluded

The authors concluded that Ramadan-style daily fasting temporarily reduces gut SCFA production and beneficial bacteria like Lactobacillus, and that the typical Ramadan diet during the fasting month may not supply enough fermentable fiber to maintain robust SCFA output — with full recovery taking roughly two months after fasting ends.

What This Means If You Fast

• SCFA dips during fasting may reflect diet, not just fasting itself. The researchers pointed to inadequate fiber intake during Ramadan meals as a likely driver — meaning what you eat during your eating window may matter as much as the fasting window itself for gut health.
• Fiber-rich foods during the eating window matter. Prioritizing vegetables, legumes, and other fermentable fiber sources when you do eat may help offset the SCFA dip this study observed.
• Don't expect instant gut microbiome benefits. This study suggests some fasting-related gut changes take weeks to months to fully play out, not days — patience matters as much with the gut-brain connection during fasting as with weight or blood sugar changes.
• Ramadan-style fasting is one specific pattern. Results here reflect a full month of daily dawn-to-dusk fasting, which is a different pattern than a daily 16:8 window — the two shouldn't be assumed to produce identical microbiome effects.
• This adds to a mixed picture on fasting and gut bacteria. Other studies, including a 5-day supervised fast that increased microbiome diversity, have found different directional effects depending on fasting length and structure.

Study Limitations

• Small sample size (n=20) with no separate non-fasting control group for direct comparison.
• Pilot/observational design — before-during-after tracking, not a randomized controlled trial, so causation can't be firmly established.
• Detailed age, gender, and health status breakdown of participants was not available in accessible source excerpts.
• Diet during Ramadan (fiber, fat, and macronutrient content of iftar/suhoor meals) was not tightly controlled, making it hard to separate fasting timing from food choice effects.
• Direct primary-source verification was limited by restricted access to the full paper at the time this article was written — figures should be cross-checked against the original publication.

Source

Jo Y et al. (2023). The Alteration of the Gut Microbiome during Ramadan Offers a Novel Perspective on Ramadan Fasting: A Pilot Study. Microorganisms, 11(8), 2106. PMID: 37630666

Frequently Asked Questions

Does intermittent fasting reduce butyrate in the gut?

This pilot study found butyrate and other short-chain fatty acids declined during a month of Ramadan-style fasting, then took about two months to fully recover afterward.

Is a drop in gut butyrate during fasting something to worry about?

The researchers framed it as likely tied to reduced fiber intake during the fasting month rather than fasting itself, and levels recovered over time — it doesn't appear to be a lasting or dangerous change.

Does fasting increase or decrease gut microbiome diversity?

This study found diversity was lower during active fasting and higher afterward, though other fasting studies have found diversity increases either during or shortly after a fast — results likely depend on fasting length and diet.

How long does it take gut bacteria to recover after a month of fasting?

In this study, short-chain fatty acid levels were still reduced 4 weeks after Ramadan ended and only rebounded by around 8 weeks post-fasting.

What can I eat to support short-chain fatty acid production while fasting?

Fermentable fiber sources — vegetables, legumes, and other prebiotic foods — eaten during the eating window are the main lever for supporting SCFA-producing bacteria like Lactobacillus.

Related Research and Articles

• A 5-day fast and 3-month Mediterranean diet increased gut microbiome diversity
• Ramadan fasting increased beneficial gut bacteria in a 2021 cohort study
• Intermittent fasting and gut health for women
• Fasting and digestive disorders: the case for giving your gut a rest
• How Ramadan fasting affects immune markers
• How fasting clears toxins from your body
• 100 years of fasting science: what has and hasn't changed

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