Ramadan fasting induces temporal gut microbiome remodeling without metabolic improvement in adults with prediabetes.

Ramadan fasting is a naturally occurring, time-restricted dietary pattern involving daily abstinence from food and drink from dawn to sunset. In this longitudinal study, we investigated the impact of Ramadan fasting on gut microbiome dynamics and metabolic outcomes in prediabetic individuals, whose responses to fasting can be uniquely altered due to decreased metabolic plasticity. Seventeen adults diagnosed with prediabetes were sampled pre-Ramadan (baseline), end of Ramadan (1-month), and 3 months post-fasting. Gut microbiome was profiled using 16S rRNA gene sequencing, and metabolic and anthropometric measurements were performed. Time-dependent coordinated changes were investigated using network-based approaches. Ramadan fasting was associated with distinct, time-dependent shifts in the gut microbiome. Genus-level richness did not change significantly across time points, while alpha diversity (Shannon and Simpson indices) increased significantly at the end of Ramadan and partially reverted by 3 months post-fasting. Beta diversity analyses showed the greatest compositional separation between baseline and 1-month, followed by partial reversion at 3 months. End-of-Ramadan samples showed the enrichment of facultative anaerobes and selected short-chain fatty acid (SCFA)-associated taxa, whereas several butyrate-producing genera increased by 3 months post-fasting, consistent with temporally phased dynamics among SCFA-associated lineages. Despite these microbial and predicted functional changes, glycemic and lipid markers remained largely unchanged, while insulin resistance and adiposity indices increased over time, and microbiome-metabolic relationships did not translate into consistent metabolic improvement. IMPORTANCE: This study shows that Ramadan fasting is associated with temporal remodeling of gut microbial composition and predicted function in individuals with prediabetes although these changes were not accompanied by clear short-term metabolic improvement. We observed coordinated shifts in bacteria linked to short-chain fatty acid production and changes in overall community balance. However, these microbial changes did not translate into measurable improvements in blood glucose or lipid levels. These findings suggest that microbiome-associated changes occurring during Ramadan fasting may not be sufficient, within the context of prediabetes, to yield measurable short-term metabolic improvement. Behavioral and metabolic restrictions may influence the extent to which microbiome-associated changes correspond with metabolic outcomes, highlighting the need for larger, diet-controlled longitudinal studies.