Glucose metabolism disorders encompass a spectrum of conditions characterized by hyperglycemia due to impaired insulin secretion, insulin resistance, or both (1). These include type 1 diabetes mellitus (T1DM), an autoimmune disorder leading to absolute insulin deficiency (2); type 2 diabetes mellitus (T2DM), characterized by insulin resistance with progressive β-cell failure (3); gestational diabetes mellitus (GDM), a transient form of glucose intolerance during pregnancy (4); and prediabetes, an intermediate state between normoglycemia and diabetes associated with increased cardiometabolic risk (5). Across these disorders, chronic hyperglycemia contributes to endothelial dysfunction, inflammation, and oxidative stress, leading to an increased risk of cardiovascular events and microvascular complications such as retinopathy, nephropathy, and neuropathy (6, 7). A key pathological feature underlying these conditions is the progressive failure of pancreatic β-cells, which leads to insufficient insulin secretion relative to metabolic demands (8).

Probiotics are live microorganisms that, when consumed in adequate amounts, confer health benefits on the host (9). Through modulation of the gut microbiota, enhancement of intestinal barrier function, and attenuation of systemic inflammation, probiotics are increasingly recognized for their potential metabolic effects (10, 11). Accumulating evidence suggests that probiotic supplementation may improve glycemic control, insulin sensitivity, and lipid metabolism in individuals with various glucose metabolism disorders, including diabetes mellitus (DM) (12, 13), prediabetes (14), and GDM (15). Proposed mechanisms include the production of short-chain fatty acids, regulation of incretin hormones such as glucagon-like peptide-1 (GLP-1), and reduction of endotoxemia and oxidative stress (16, 17), all of which may indirectly support β-cell preservation and function. However, despite the growing interest in this area, the specific impact of probiotics on islet β-cell function remains under-investigated (18). The homeostasis model assessment of β-cell function (HOMA-β), derived from fasting insulin and glucose levels, serves as a non-invasive and practical tool to estimate insulin secretory capacity (19). While several clinical trials have assessed the effect of probiotic supplementation on HOMA-β, results have been inconsistent and lack a comprehensive synthesis (20–31). Therefore, the aim of this meta-analysis was to systematically evaluate the effect of probiotics on islet β-cell function, measured by HOMA-β, in individuals with glucose metabolism disorders.

The guidelines set forth by PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) (32, 33) and the Cochrane Handbook (34) were followed in the design and performance of the study. The protocol of the meta-analysis was registered at PROSPERO with the identifier CRD420251087101.

This meta-analysis synthesized current evidence from 12 RCTs and demonstrated that probiotic supplementation significantly improves islet β-cell function, as reflected by HOMA-β, in individuals with glucose metabolism disorders. While considerable heterogeneity was observed across the included studies (I² = 92%), this represents an important limitation of our analysis. The sensitivity analysis restricted to high-quality RCTs did not show a significant effect of probiotics on HOMA-β, suggesting that study quality may partly explain the inconsistent findings. Therefore, the pooled results should be interpreted with caution and considered exploratory rather than definitive. Our subgroup and meta-regression analyses indicated that baseline HbA1c was a major effect modifier, explaining more than 60% of the heterogeneity, which suggests that differences in baseline glycemic control are likely a key driver of variability across studies. Nevertheless, residual heterogeneity remained, and the possibility that the overall positive effect was influenced by lower-quality trials cannot be excluded. These observations highlight the need for future large-scale, rigorously designed RCTs with standardized probiotic formulations and longer follow-up to more definitively determine the impact of probiotics on β-cell function. While the overall mean difference in HOMA-β was statistically significant, its clinical relevance remains uncertain. There is currently no universally accepted minimal clinically important difference (MCID) for HOMA-β, and prior studies rarely define thresholds for meaningful improvement. The lower bound of the 95% CI (0.23%) suggests that, for some patients, the absolute change may be too small to produce measurable clinical benefit. Therefore, the observed improvement should be interpreted as hypothesis-generating rather than conclusive for clinical decision-making.

Compared with recent meta-analyses focusing on probiotics in specific populations or general glycemic outcomes (41, 42), our study provides a broader, cross-disorder analysis specifically targeting β-cell function, incorporating data across T1DM, T2DM, GDM, and prediabetes. The identification of baseline HbA1c ≥ 8.5% as a key effect modifier, explaining 62.5% of the heterogeneity, suggests that probiotic benefits may be most pronounced in patients with poor glycemic control, offering clinically relevant insights for personalized therapy. Although the overall effect size (MD: 3.04%) was smaller than in some prior reports, this likely reflects differences in study populations, intervention heterogeneity, and analytic methods. By providing updated evidence through May 2025 and systematically exploring heterogeneity sources, our analysis refines the understanding of probiotics’ role in metabolic health while emphasizing the need for standardized interventions, longer-term RCTs, and mechanistic studies to translate these findings into clinical recommendations. This meta-analysis focused on HOMA-β because β-cell function has been rarely evaluated in previous probiotic meta-analyses, which predominantly examined glycemic control indices such as HbA1c or fasting glucose. Although single-sample HOMA modeling has greater intra-subject variability than multiple-sample approaches, it remains the most widely used and feasible method for β-cell function assessment in clinical trials, enabling standardized comparisons across studies. Consistent with our results, Singh et al. reported significant reductions in HbA1c, fasting glucose, and HOMA-IR in T2DM patients receiving probiotics, suggesting metabolic benefits beyond glycemic control alone (43). However, while Singh et al. focused on glycemic indices in T2DM, our analysis specifically evaluated β-cell function (HOMA-β) across diverse glucose metabolism disorders. The comparison highlights that although probiotics may improve glucose homeostasis in T2DM, their effects on β-cell function remain less established and may be more pronounced in patients with poor baseline glycemic control, as suggested by our subgroup analyses.

The beneficial effect of probiotics on HOMA-β can be attributed to several plausible physiological mechanisms. Probiotics have been shown to influence host metabolism through modulation of the gut microbiota, leading to increased production of short-chain fatty acids (SCFAs) such as butyrate, propionate, and acetate (44, 45). These metabolites improve insulin sensitivity, enhance GLP-1 secretion, and reduce systemic inflammation—all of which indirectly support β-cell function (46, 47). Furthermore, probiotics can strengthen intestinal barrier integrity, thereby reducing the translocation of endotoxins and lowering chronic low-grade inflammation (48, 49), which is known to impair β-cell survival and function (50). Some probiotic strains may also exert antioxidant effects or directly interact with enteroendocrine and immune cells, creating a more favorable metabolic and inflammatory environment for insulin secretion (51, 52). However, the core molecular pathways that mediate the benefit of probiotics on islet β-cell function remain to be determined in future studies. Importantly, no included RCT directly investigated the mechanistic effects of probiotics on β-cell function. Therefore, the proposed pathways, including modulation of gut microbiota, SCFA production, incretin regulation, and anti-inflammatory effects, remain largely speculative and are extrapolated from preclinical or indirect evidence. These mechanisms require confirmation in dedicated mechanistic studies before firm conclusions can be drawn.

An important and novel finding of this study lies in the differential impact of probiotics based on baseline HbA1c levels. Subgroup analysis revealed that probiotic supplementation significantly improved HOMA-β in individuals with a baseline HbA1c ≥ 8.5%, while no significant benefit was observed in those with a HbA1c < 8.5%. This finding was further supported by meta-regression analysis, which showed a positive association between baseline HbA1c and the magnitude of improvement in HOMA-β. One potential explanation for this finding is that individuals with poorly controlled glycemia experience greater gut dysbiosis, increased endotoxemia, and more pronounced β-cell stress, rendering them more responsive to the anti-inflammatory and metabolic effects of probiotics (53). In contrast, those with mild hyperglycemia may already have relatively preserved β-cell function and less microbial imbalance, limiting the potential for measurable improvement. These findings suggest that the metabolic benefits of probiotics may be most pronounced in patients with more severe glucose dysregulation, supporting the rationale for targeted supplementation strategies. Importantly, the significant improvement in HOMA-β was observed only in patients with HbA1c ≥ 8.5%, whereas those with HbA1c < 8.5% showed no benefit. This finding suggests that the overall pooled effect may be driven primarily by patients with poor baseline glycemic control, who likely have greater β-cell dysfunction and metabolic stress. Clinically, this indicates that probiotic supplementation, if beneficial, might be most appropriate for selected high-risk populations rather than applied broadly to all individuals with glucose metabolism disorders. Future trials should therefore stratify analyses by baseline glycemic status and explore whether targeted supplementation yields clinically meaningful metabolic improvements. In addition, because our meta-regression was performed using study-level rather than individual-level data, the results are subject to ecological fallacy, and individual-level associations cannot be directly inferred. Moreover, although baseline HbA1c explained 62.5% of the between-study heterogeneity, considerable residual variability remains, suggesting that additional unmeasured factors likely influence the effect of probiotics on β-cell function.

Notably, the sensitivity analysis, including only high-quality RCTs, showed no significant effect of probiotics on HOMA-β, and heterogeneity, although reduced, remained moderate (I² = 63%). This finding underscores that methodological limitations and clinical diversity—such as probiotic strain composition, CFU dose, and treatment duration—likely contributed to the observed heterogeneity. Therefore, the pooled results should be considered exploratory rather than definitive, highlighting the need for larger, rigorously designed RCTs with standardized interventions to clarify the true effect of probiotics on β-cell function.

This meta-analysis has several notable strengths. First, the literature search was comprehensive and up to date, covering multiple major databases through May 2025 and including only RCTs, thereby enhancing the internal validity of the findings. Second, the analysis included a wide spectrum of glucose metabolism disorders (e.g., DM, GDM, and prediabetes), improving generalizability to various clinical contexts. Third, extensive subgroup and meta-regression analyses were conducted to explore the influence of study-level covariates, such as age, sex, BMI, baseline HbA1c, and HOMA-β, treatment duration, and concurrent hypoglycemic therapy. These exploratory analyses allowed for the identification of baseline HbA1c as a key determinant of probiotic efficacy, helping to clarify heterogeneity and support the robustness of the primary outcome.

Nonetheless, some limitations should be acknowledged. First, the follow-up durations of the included RCTs were relatively short (6–24 weeks), so the long-term sustainability and clinical significance of the observed improvements remain uncertain. Future large-scale trials with extended follow-up are warranted to determine whether probiotic supplementation yields durable metabolic benefits. On the other hand, although subgroup analysis by treatment duration showed no significant effect modification, this may be due to insufficient statistical power rather than the true absence of a duration effect. Future adequately powered RCTs with longer intervention periods are required to clarify whether treatment duration influences the metabolic benefits of probiotics. Second, we restricted the search to English and Chinese publications, which may introduce language bias and limit the generalizability of our findings, although these languages account for a substantial proportion of probiotic research output. The geographic concentration of included studies, primarily from Asia, and the restriction to English and Chinese publications, raise the possibility of publication and language bias. Moreover, not all included trials were placebo-controlled, and several used open-label designs, which introduce potential performance bias (23, 25, 26, 29). Although the outcome measure of HOMA-β is laboratory-based and less susceptible to subjective bias, lack of blinding may still influence study conduct and participant adherence. The overall number of included studies and sample size remained limited, which constrained the power of some subgroup comparisons and limited our ability to assess publication bias with a high degree of certainty, and selective reporting cannot be completely ruled out, especially in trials without pre-registered protocols. Another limitation of this study is the clinical heterogeneity of the included populations. Our analysis pooled participants with prediabetes, T2DM, GDM, and diabetes with complications, which represent distinct conditions with differing pathophysiology, clinical course, and treatment responses. The wide range of baseline HbA1c values (5.7–10.4%) and BMI (22.0–32.6 kg/m²) reflects this diversity and may have contributed to the heterogeneity of the results. We chose to pool these groups because the number of eligible RCTs reporting HOMA-β was limited, and all of these conditions share impaired β-cell function as a central feature. Nevertheless, this approach introduces methodological limitations, and the pooled estimates should be interpreted as exploratory. Our subgroup and meta-regression analyses suggest that baseline glycemic status, particularly HbA1c level, rather than diagnostic category per se, was the primary modifier of the observed probiotic effect. Future RCTs are needed to evaluate the impact of probiotics within specific, clinically homogeneous populations to provide more definitive conclusions. Additionally, the composition, strains, dosage, and duration of probiotic interventions varied widely across studies, which may have introduced clinical heterogeneity and influenced outcomes in ways not fully captured by the subgroup analyses. Specifically, the included studies used diverse probiotic formulations, ranging from single- to multi-strain products with different species and CFU counts. Such variability likely contributes to the clinical heterogeneity observed and limits the generalizability of our findings. Without standardized probiotic preparations, it remains difficult to provide specific clinical recommendations, underscoring the need for future trials with uniform interventions to clarify efficacy. Moreover, the inclusion of open-label studies with unclear randomization methods likely introduced performance and detection bias. Although HOMA-β is a laboratory-based outcome, lack of blinding may still affect study conduct, participant adherence, or laboratory handling. The sensitivity analysis excluding high-risk studies showed no significant effect, underscoring that the overall findings should be interpreted with caution. In addition, while HOMA-β is a widely accepted surrogate marker for β-cell function, it does not directly measure insulin secretion dynamics and may be affected by concurrent insulin resistance. Moreover, crossover studies were excluded to avoid carryover effects and enhance methodological consistency; no major crossover trials meeting eligibility criteria were identified that would likely alter our conclusions. Finally, it should be acknowledged that there is no universally accepted overarching definition or standardized index for “glucose metabolism disorders.” In this meta-analysis, we operationally defined this spectrum to include T1DM, T2DM, GDM, and prediabetes, based on diagnostic criteria reported in the original studies. Although this approach reflects their shared pathophysiological basis of hyperglycemia and β-cell dysfunction, the lack of a universal definition may introduce variability across studies and represents an inherent limitation of our work.

From a clinical perspective, the mean difference of 3.04% in HOMA-β represents a modest but statistically significant improvement in insulin secretory function. While the absolute clinical impact of this magnitude is difficult to interpret in isolation, the subgroup findings suggest that specific patient populations—particularly those with suboptimal glycemic control—may derive more substantial metabolic benefit. Given the safety profile and accessibility of probiotic supplementation, these results support its potential use as an adjunctive strategy for patients with glucose metabolism disorders, especially those with elevated HbA1c or early β-cell dysfunction (54). However, it remains unclear whether the observed improvements in HOMA-β translate into meaningful long-term outcomes, such as reduced need for pharmacotherapy, delayed disease progression, or fewer complications. Future research should aim to address several gaps. Large-scale, well-designed RCTs are needed to validate the effect of probiotics on β-cell function using more direct and dynamic measures, such as insulin secretion rates during oral glucose tolerance tests or mixed-meal tolerance tests, and the gold standard of the hyperglycemic clamp technique (55). Trials should aim for longer durations, standardized probiotic formulations, and rigorous blinding protocols. In addition, studies should assess whether improvements in HOMA-β are sustained over time and lead to clinical endpoints such as improved HbA1c control, reduced medication burden, or prevention of diabetes onset in high-risk individuals. Exploring microbiome profiles as predictive biomarkers of response may also help tailor probiotic therapy more precisely (56).

It should also be noted that the use of HOMA-β as the primary outcome carries important limitations. Single-sample HOMA-β has been reported to show higher intrasubject variability (coefficient of variation ≈7–8%) compared with repeated-sample approaches (≈4%), which may reduce measurement precision (57). Furthermore, HOMA-β does not always correlate linearly with insulin secretory capacity across different stages of glucose tolerance, and its interpretation can be complex in individuals with significant insulin resistance (58). Unlike dynamic tests such as the hyperglycemic clamp or oral glucose tolerance test, HOMA-β provides only an indirect, surrogate estimate of β-cell function. However, HOMA-β remains the most widely used and consistently reported measure of β-cell function in clinical trials, making it the only feasible parameter for meta-analysis across heterogeneous studies. We therefore emphasize that our results should be interpreted with caution and as hypothesis-generating, while future high-quality RCTs should incorporate more robust and standardized dynamic methods to better assess the impact of probiotics on β-cell function. Finally, it is important to recognize that, despite growing interest, the clinical evidence supporting probiotics for improving β-cell function in glucose metabolism disorders remains conflicting. No consensus statement or official guideline currently endorses the use of probiotics for this purpose. Our findings, therefore, should not be interpreted as a recommendation for clinical practice, but rather as hypothesis-generating evidence that may help guide future investigations. Large-scale, standardized, and longer-term RCTs will be essential to establish whether probiotic supplementation confers reproducible metabolic benefits and whether these findings can ultimately inform clinical guidelines.

In summary, this meta-analysis suggests that probiotic supplementation may modestly improve islet β-cell function, as assessed by HOMA-β, in adults with glucose metabolism disorders. However, these findings should be interpreted with caution. Substantial statistical heterogeneity was present, and sensitivity analysis limited to high-quality studies did not confirm a significant benefit, raising the possibility that the pooled positive effect was influenced by lower-quality trials. In addition, the clinical diversity of the included populations—ranging from prediabetes to T2DM, GDM, and diabetes with complications—introduces methodological limitations, as these conditions differ in pathophysiology and treatment response. The reliance on HOMA-β as a surrogate outcome, which is subject to variability and interpretive complexity, further restricts the certainty of our conclusions.

At present, evidence regarding probiotic supplementation in this context remains conflicting, and no consensus statement or clinical guideline recommends probiotics to improve β-cell function in patients with glucose metabolism disorders. Therefore, our results should be regarded as exploratory and hypothesis-generating rather than conclusive. Future large-scale, rigorously designed RCTs are needed, incorporating standardized probiotic formulations, longer intervention and follow-up periods, and more robust dynamic assessments of β-cell function. Such studies will be essential to determine whether probiotics provide consistent clinical benefits and whether their use should ultimately be considered in clinical practice.