Ramadan Fasting Increases Beneficial Gut Bacteria by Up to 73% in 30 Days: 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 at Erasmus University Rotterdam wanted to understand what 30 days of daily intermittent fasting — the kind practised during Ramadan — does to the community of microorganisms living in the human gut. The gut microbiome influences everything from metabolism and immune function to mood and inflammation, but at the time of this study, very little controlled human data existed on how IF-style fasting specifically affects its composition.

The team collected stool samples and blood before, during, and after Ramadan to track changes in gut bacteria diversity, the relative abundance of key bacterial families, and associated metabolic parameters. This article is closely related to the broader topic of how intermittent fasting affects gut health and the role of autophagy in fasting.

Who Was Studied

Participant profile: Male volunteers; 2 separate cohorts enrolled and sampled in 2 different calendar years to validate findings. Exact age range and baseline BMI were not extracted from the available abstract.

How Ramadan fasting worked in this study: Participants fasted from Fajr (dawn prayer) to Maghrib (sunset prayer), creating a daily fasting window of approximately 14–16 hours depending on the season and latitude. No food or drink was consumed during the fasting window. Eating, drinking, and supplementation were permitted freely during the night-time hours. No calorie targets or specific dietary instructions were given — participants ate according to personal preference during the eating window.

What the Researchers Found

Gut Microbiome Diversity

Ramadan-associated intermittent fasting significantly altered the structure of the gut microbiome within the 30-day fasting period. Both the diversity and composition of the microbial community changed in the fasting group compared with controls.

Bacterial Taxa: What Changed

Both of these families are producers of short-chain fatty acids (SCFAs) — particularly butyrate — which are the primary energy source for the cells lining the gut wall. Higher SCFA production is associated with reduced intestinal permeability, lower inflammation, and improved metabolic regulation.

The changes in Lachnospiraceae concentrations specifically mirrored fasting-provoked changes in physiological parameters, suggesting this bacterial family may be a mediator — rather than just a bystander — of fasting's metabolic effects.

Metabolic Parameters

The fasting group showed improvements in metabolic parameters over the 30-day period. Specific numerical values for individual markers such as BMI, fasting glucose, and lipid panels were not available from the extracted abstract data, but the study reported improved metabolic outcomes concomitant with microbiome changes.

What Did Not Change (Key Finding)

• Microbiome changes were not permanent. After Ramadan ended and participants returned to their usual eating patterns, gut microbiome composition returned to its pre-fasting baseline. This is one of the study's most significant findings — and its most important limitation. The benefits appear to be driven by the ongoing practice of fasting, not by a permanent structural change.

What the Researchers Concluded

The researchers concluded that Ramadan-associated intermittent fasting remodels the gut microbiome by increasing short-chain fatty acid producing bacteria, and that these changes occur in parallel with improvements in metabolic parameters. They suggested that the microbiome may act as a mediating pathway through which intermittent fasting exerts its metabolic benefits — not just a secondary effect.

What This Means If You Fast

• Your gut bacteria respond rapidly to fasting. Within 30 days of 16-hour daily fasting, the relative abundance of health-associated bacterial families increased by 61–73%. This is a substantial shift in a short timeframe.
• The bacteria that increase are specifically beneficial. Lachnospiraceae and Ruminococcaceae are butyrate-producing families. Butyrate feeds the gut lining, reduces intestinal inflammation, and appears to be linked to better metabolic control — including how the body handles glucose and fat.
• The link between microbiome and metabolism is direct. The correlation between Lachnospiraceae changes and physiological parameter changes suggests the gut microbiome is not just responding to fasting — it may be part of why fasting improves metabolic health. This reinforces the importance of understanding how intermittent fasting improves insulin sensitivity.
• Consistency matters more than occasional fasting. Because changes reversed when fasting stopped, this study suggests that the gut-health benefits of IF require ongoing practice — not a one-month intervention. Daily intermittent fasting appears to be more beneficial for the microbiome than occasional fasts.
• Food choices during the eating window still matter. Because Ramadan eating includes significant dietary diversity (and often very high-calorie night meals), the microbiome benefits appear to be driven specifically by the fasting window itself rather than the food consumed — a meaningful finding for IF practitioners at any latitude.
• Male-only findings need replication in women. The exclusively male sample means we cannot yet draw firm conclusions about whether women experience the same microbiome changes during fasting. Women's hormonal cycle affects how fasting works, and this may include microbiome responses.

Study Limitations

• Small sample size: Only 27 fasting participants and 10 controls — too small to draw population-level conclusions
• Male participants only: All volunteers were male; results may not apply equally to women
• Observational design: Not a randomized controlled trial. Participants self-selected into fasting (those who observe Ramadan); controls were not randomly assigned
• Uncontrolled diet: No dietary standardisation during the eating window — Ramadan night eating often includes large, varied meals that differ significantly from typical daily eating patterns
• Two-cohort design: Data from 2 separate years were combined, introducing potential year-to-year variability
• Reversion finding: The reversal of microbiome changes after fasting ended limits claims about long-term benefits; ongoing practice appears necessary to maintain effects
• Incomplete metabolic data: Specific numerical values for metabolic markers were not available for this article summary
• Ethnicity and setting: Participants were likely from a specific geographic/ethnic background; generalisability to other populations is unclear

Source

Su J, Wang Y, Zhang X, Ma M, Xie Z, Pan Q, Ma Z, Peppelenbosch MP. (2021). Remodeling of the gut microbiome during Ramadan-associated intermittent fasting. The American Journal of Clinical Nutrition, 113(5), 1332–1342. DOI: 10.1093/ajcn/nqaa388. PMID: 33842951

Frequently Asked Questions

Does Ramadan fasting improve gut health?

Based on this study, yes — within 30 days of 16-hour daily fasting during Ramadan, participants showed a 61–73% increase in the relative abundance of beneficial SCFA-producing gut bacteria (Lachnospiraceae and Ruminococcaceae). These bacteria are strongly associated with better gut barrier integrity and metabolic health.

How long does it take for fasting to change the gut microbiome?

This study observed significant changes within a single 30-day Ramadan fasting period. Other research suggests that dietary changes can alter the gut microbiome in as little as 3–4 days, but the magnitude of change increases with sustained practice.

Do the gut microbiome benefits of fasting last permanently?

Based on this study, no. Microbiome composition returned to baseline once participants returned to normal eating. This suggests that the benefits require ongoing, consistent fasting practice rather than a single fasting period.

Which gut bacteria increase during Ramadan fasting?

The study found significant increases in two bacterial families: Lachnospiraceae (24.6% → 39.7%) and Ruminococcaceae (13.4% → 23.2%). Both are major producers of short-chain fatty acids — particularly butyrate — which fuel the gut lining and reduce inflammation.

Is 16-hour fasting enough to change the gut microbiome?

According to this study, yes. A 16-hour daily fasting window (sunrise to sunset) produced clinically meaningful changes in gut microbiome composition over 30 days. The fasting window itself — rather than calorie restriction — appears to be the key driver, since dietary choices during Ramadan night meals vary widely.

Related Research and Articles

• How intermittent fasting improves gut health
• What is autophagy and when does it start during fasting?
• Intermittent fasting and inflammation: the research explained
• Can intermittent fasting improve insulin sensitivity?
• What happens to your body hour by hour when you fast
• Intermittent fasting benefits: the complete science-backed guide
• Does intermittent fasting reduce inflammation?

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