Gut Microbes Take Center Stage in the Renamed Ovarian Syndrome PMOS

One of the most common endocrine disorders in women may have a hidden accomplice living in the gut. Polyendocrine metabolic ovarian syndrome, or PMOS, the new global name for what was long called polycystic ovary syndrome, affects an estimated 10 to 15 percent of women of reproductive age and is defined by hyperandrogenism, ovulatory dysfunction, and polycystic ovarian morphology under the Rotterdam criteria, which require two of three features after excluding other causes of androgen excess. It is frequently accompanied by insulin resistance, obesity, and chronic low-grade inflammation, and carries long-term risks of type 2 diabetes and cardiovascular disease. Now a comprehensive review published in Experimental Biology and Medicine argues that the trillions of microbes inhabiting the intestine are not bystanders in this disorder but a critical regulatory node within an integrated gut–metabolism–endocrine–ovary axis, a framework that could reshape how scientists and clinicians think about the syndrome’s bewildering heterogeneity.

The review, led by Shengyue Jin and colleagues at the Department of TCM Gynecology of Hangzhou TCM Hospital of Zhejiang Chinese Medical University, was designed as a narrative review with a systematic literature search. The team queried PubMed, Web of Science, Embase, and the China National Knowledge Infrastructure from database inception to March 2026, using terms related to PMOS, gut microbiota, microbial metabolites, and microbiota-targeted interventions. Two authors independently screened records, resolved disagreements by consensus, and excluded case reports, letters, conference abstracts, and non-English publications. No meta-analysis was performed. What distinguishes this synthesis from earlier descriptive reviews, the authors contend, is its explicit incorporation of phenotypic heterogeneity, methodological variability, and evidence grading across clinical and preclinical studies, moving the field beyond fragmented associative observations toward a structured, system-level perspective.

The gut microbiota, sometimes described as the host’s second genome, is dominated by the phyla Bacteroidetes and Firmicutes, with contributions from Proteobacteria, Verrucomicrobia, Actinobacteria, and others. It performs essential functions in digestion, energy harvest, vitamin synthesis, immune modulation, and endocrine regulation, and has been recognized as an endocrine-like organ that interacts with sex hormones and insulin. A healthy gut is marked by high bacterial diversity, an intact intestinal barrier maintained by tight junction proteins, and an abundance of beneficial genera such as Bifidobacterium and Lactobacillus. Dysbiosis, by contrast, involves a loss of beneficial microbes, an overgrowth of pro-inflammatory species, and compromised barrier integrity. Accumulating evidence indicates that PMOS is associated with precisely this pattern: decreased microbiota diversity, reduced beneficial bacteria, and increased pro-inflammatory taxa.

Crucially, the relationship runs in both directions. Elevated androgen levels, a hallmark of PMOS driven by enhanced ovarian steroidogenesis, increased adrenal androgen secretion, and insulin resistance, have been linked to reduced gut microbiota diversity, an increased Firmicutes-to-Bacteroidetes ratio, and enrichment of genera including Clostridium, Dorea, and Bilophila. Dihydrotestosterone-induced PMOS rat models show increased body weight, fat deposition, and diminished intestinal flora diversity. Insulin resistance, which affects roughly 50 to 70 percent of PMOS patients, further reshapes microbial ecology: among women with insulin resistance, Bacteroidaceae abundance rises while Prevotellaceae falls, and patients exhibit elevated lipopolysaccharide biosynthesis pathways and heightened inflammatory cytokines. Obesity, present in about half to 60 percent of PMOS cases, amplifies these alterations, with obese patients showing higher concentrations of LBP, GLP-2, succinate, and zonulin family peptides, implying heightened intestinal permeability and compromised barrier function.

The review’s central mechanistic contribution lies in its dissection of microbiota-derived metabolites that link intestinal dysbiosis with metabolic and endocrine dysfunction. Bile acids, regulated through the receptors TGR5 and FXR, emerge as a signaling hub. Animal studies show that ursodeoxycholic acid enhances ovarian morphology and decreases testosterone and insulin levels, while clinical data reveal that elevated Bacteroides, glycodeoxycholic acid, and tauroursodeoxycholic acid correlate with insulin resistance and ovarian dysfunction. Bile acids enhance IL-22 secretion by activating the GATA3 pathway in innate lymphoid cells, and primary bile acid proportions correlate positively with total testosterone and free androgen index, suggesting roles in hyperandrogenism, follicular development, and ovulatory disorders.

Short-chain fatty acids, produced by microbial fermentation of dietary fiber, act as the counterweight. Circulating butyrate is significantly reduced in obese PMOS patients, and butyrate impedes METTL3-mediated FOSL2 m6A methylation, obstructing NLRP3 inflammasome activation and pro-inflammatory cytokine release. SCFAs enhance IL-22 secretion via GPR41 signaling and HDAC inhibition, fortify the intestinal mucosal barrier, and restrain pro-inflammatory responses in dendritic cells and macrophages by activating GPR41/43 and GPR109A receptors, decreasing IL-6 and IL-12 while facilitating Treg differentiation and IL-10 secretion. Given that PMOS patients display Treg/Th17 imbalance, SCFA-mediated restoration of immune homeostasis may represent a viable strategy. SCFAs also stimulate incretin production through FFAR2/3, augmenting glucose-dependent insulin secretion and improving HOMA-IR.

On the damaging side of the ledger, branched-chain amino acids and lipopolysaccharide function as amplifiers of metabolic dysregulation. The BCAA metabolite 3-HIB enhances transendothelial fatty acid transport, stimulating lipid deposition in skeletal muscle and contributing to insulin resistance, while excess BCAAs trigger the mTORC1/S6K1 pathway and disrupt mitochondrial function. Elevated plasma BCAA levels correlate positively with androgen levels, antral follicles, and menstrual irregularity, with PPM1K identified as a causative gene. LPS, a structural component of Gram-negative bacteria, enters the bloodstream through a leaky intestinal barrier, inducing metabolic endotoxemia. It activates the TLR4/NF-κB inflammatory pathway, stimulates TNF-α, IL-1β, IL-6, and IL-8 in granulosa cells, and initiates oxidative stress. Fecal metagenomic data suggest that reduced Bacteroidales may elevate pro-inflammatory LPS levels in follicles, correlating with follicular hypoplasia and elevated AMH.

These mechanistic insights are fueling a wave of microbiota-targeted interventions. Lifestyle modification remains foundational, with ketogenic and Mediterranean diets improving anthropometric, metabolic, and sex hormone profiles, and exercise modalities from high-intensity interval training to yoga enhancing insulin sensitivity and menstrual regularity. Fecal microbiota transplantation from healthy donors partially reduced fat accumulation and modified metabolism-associated bacteria in DHT-induced PMOS mice, while in letrozole-induced rats it enhanced estrous cyclicity, decreased serum androgens, and restored normal ovarian morphology, though no human trials have yet evaluated FMT safety or efficacy in PMOS. Probiotic strains including Lactobacillus plantarum HL2 and Bifidobacterium longum HB3 ameliorated ovarian pathology and diminished testosterone in animal models. Prebiotics show particular promise: inulin supplementation improved glucose tolerance, insulin sensitivity, and ovarian morphology in PMOS models, and a clinical investigation found that 10 grams of inulin daily over three months improved hyperandrogenism, insulin resistance, and dyslipidemia while increasing Bifidobacterium abundance.

Pharmacological agents also intersect with the gut ecosystem. Metformin enhances beneficial bacteria including Akkermansia muciniphila, Clostridium leptum, and Faecalibacterium prausnitzii, reduces plasma LPS and inflammatory mediators, and may normalize altered fecal SCFA levels. GLP-1 receptor agonists such as semaglutide and liraglutide improve weight, hyperandrogenism, and menstrual cyclicity, with semaglutide acting through PI3K/AKT/mTOR and AMPK/SIRT1/NF-κB pathways in animal models. Natural compounds add further depth: resveratrol activates SIRT1/AMPK signaling, inhibits CYP17A1 and HMG-CoA reductase to reduce androgen synthesis, and exerts a prebiotic-like effect on gut microbiota, while berberine restores microbial diversity and structure in PMOS patients. Traditional Chinese medicine formulations including Bailing capsule modulate the LPS-TLR4 inflammatory pathway and enrich SCFA-producing bacteria.

Yet the authors are emphatic about the limits of current evidence. Most included studies are observational or cross-sectional, with a scarcity of large-scale randomized controlled trials and long-term prospective cohort data, leaving causal inference weak. Substantial heterogeneity exists across studies in microbial detection techniques, from 16S rRNA gene sequencing to metagenomic and metabolomic approaches, and in study populations differing in ethnicity, obesity status, and PMOS phenotypic classification. Microbiota-targeted interventions are more likely to exert adjunctive therapeutic effects by improving the metabolic and inflammatory microenvironment rather than serving as independent treatments, and their stability, efficacy reproducibility, and clinical generalizability remain unvalidated. The review calls for well-designed longitudinal studies and randomized controlled trials with strict phenotypic stratification, integrating causal inference approaches and multi-omics analyses. As understanding of the gut–metabolism–endocrine–ovary axis advances, precision intervention strategies based on individual gut microbiota characteristics may offer new therapeutic directions for the long-term management of PMOS and improved overall patient health outcomes.

Subject of Research: Gut microbiota and PMOS: an integrated gut–metabolism–endocrine–ovary axis

Article Title: Gut microbiota and polyendocrine metabolic ovarian syndrome: an integrated gut–metabolism–endocrine–ovary axis

Article References: Jin, S., Zhu, M., Lu, Y., Zhao, J., Zhu, J., & Fang, X. (2026). Gut microbiota and polyendocrine metabolic ovarian syndrome: an integrated gut–metabolism–endocrine–ovary axis. Experimental Biology and Medicine, 251, Article 11058. https://doi.org/10.3389/ebm.2026.11058

Image Credits: AI Generated

DOI: 10.3389/ebm.2026.11058

Keywords: gut microbiota, PMOS, PCOS, insulin resistance, hyperandrogenism, bile acids, short-chain fatty acids, microbiome, endocrinology, ovarian dysfunction, microbiota, polyendocrine