Intermittent Fasting and Probiotics for Gut Microbiota Modulation in Type 2 Diabetes Mellitus: A Narrative Review

Background: Type 2 diabetes mellitus (T2DM) is a global epidemic in which gut microbiota dysbiosis contributes to impaired glucose homeostasis and chronic inflammation. Intermittent fasting (IF) and probiotic supplementation have independently demonstrated glycemic benefits in T2DM, largely through microbiota remodeling. This narrative review synthesizes evidence up to October 2025 to clarify the microbiota-dependent mechanisms of IF and probiotics, and to evaluate the biological plausibility and preliminary clinical data for their combined application in T2DM management. Methods: We conducted a comprehensive literature review of preclinical and clinical studies (PubMed, Embase, Web of Science, and Cochrane Library) examining IF regimens (primarily time-restricted feeding and 5:2 protocols) and multi-strain probiotics containing Lactobacillus and Bifidobacterium species in T2DM or relevant models. Mechanistic pathways, microbial compositional shifts, and metabolic outcomes were qualitatively synthesized, with emphasis on overlapping signaling (short-chain fatty acids, bile acids, GLP-1, and barrier function). Results: IF consistently increases Akkermansia muciniphila and, variably, Faecalibacterium prausnitzii abundance, restores microbial circadian rhythmicity, and enhances SCFA and secondary bile acid production. Multi-strain probiotics modestly reduce HbA1c (-0.3% to -0.6%) and fasting glucose, outperforming single-strain preparations. Both interventions converge on reduced endotoxaemia and improved intestinal integrity. Preclinical models indicate potential synergy, whereas the only direct human trial to date showed neutral results. Conclusions: IF and probiotics engage overlapping microbiota-mediated pathways, supporting their combined use as an adjunctive strategy in T2DM. Adequately powered randomized trials incorporating deep metagenomics, metabolomics, and hard clinical endpoints are now required to confirm additive or synergistic efficacy.