Ramadan intermittent fasting and the gut microbiome: modulation of diversity and implications for metabolic health

Ramadan fasting (RF), a culturally embedded form of time-restricted eating, involves daily abstinence from food and drink from dawn to sunset and provides a real-world human model to examine the potential impact of intermittent fasting on the gut microbiome and metabolic health. This review synthesizes evidence from human studies, predominantly observational in design, to evaluate the associations between RF, microbial composition and diversity, and metabolic outcomes. Current evidence suggests that RF may be associated with changes in gut microbial richness and community structure, including reported increases in taxa such as Akkermansia muciniphila, Faecalibacterium prausnitzii, Roseburia, and Bacteroides, many of which are linked to short-chain fatty acid (SCFA) production and intestinal barrier function. However, findings across studies are not entirely consistent, particularly with respect to microbial taxa abundance and SCFA levels. Observational studies also report concurrent changes in anthropometric and metabolic parameters, including body weight, lipid profiles, glycemic markers, and inflammatory indices, although these associations may be influenced by confounding factors such as dietary composition, lifestyle changes, and weight loss during Ramadan. Proposed mechanisms include alterations in feeding-fasting rhythms and microbiota-related pathways such as bile acid metabolism and gut barrier function; however, these mechanisms are largely inferred from related experimental models and should be considered hypothesis-generating in the context of RF. Therefore, while RF represents a relevant ecological model for studying time-restricted eating in humans, the current evidence remains limited by small sample sizes, interindividual variability, and methodological heterogeneity. Further well-controlled, longitudinal, and multi-omics studies are required to clarify causal relationships and determine the extent to which RF-associated microbial changes contribute to metabolic health.