Probiotics and PCOS: The Emerging Connection, A Review for Dietitians

Polycystic ovary syndrome (PCOS) is a common endocrine disorder affecting 8-13% of reproductive-aged individuals worldwide. It is characterized by excess androgens (testosterone, androstenedione, DHEAS), leading to symptoms such as irregular periods, acne, and excess hair growth (hirsutism).

A key driver of this imbalance is insulin resistance, which contributes to both increased androgen production and long-term metabolic risks.

Emerging research highlights the gut microbiome's involvement in PCOS, revealing that individuals with PCOS often have lower microbial diversity and an altered gut microbiota composition. Probiotics are being explored as a potential adjunct therapy for PCOS, offering benefits such as improved insulin sensitivity, reduced inflammation, and hormonal regulation.

Gut Microbiota and PCOS

Research comparing the gut microbiome of individuals with PCOS to healthy controls has identified specific bacterial imbalances that may contribute to the metabolic and hormonal disturbances seen in PCOS.

Women with PCOS exhibit higher levels of pro-inflammatory bacteria such as:

Escherichia/Shigella: May produce lipopolysaccharides (LPS), which trigger systemic inflammation and insulin resistance by increasing gut permeability
Bacteroides: May contribute to metabolic endotoxemia and chronic inflammation
Clostridium: May also contribute to increased androgen levels and metabolic dysfunction

They also show a reduced abundance of beneficial bacteria like:

Lactobacillus
Bifidobacterium
Akkermansia

Those who have a healthier microbiome balance demonstrate a higher proportion of short-chain fatty acid (SCFA)-producing bacteria, which support insulin sensitivity and reduce inflammation.

Research also suggests that individuals with PCOS have lower levels of the gut hormones ghrelin and Peptide YY (PYY). This may contribute to impaired appetite regulation, insulin resistance, and metabolic dysfunction. The gut microbiome influences ghrelin and PYY secretion by producing short-chain fatty acids (SCFAs), modulating gut hormone signaling, and enhancing insulin sensitivity.

These findings suggest that the gut microbiome plays a crucial role in PCOS pathophysiology and that interventions aimed at restoring microbial balance, such as probiotic supplementation, may be beneficial.

Do Probiotics Reduce PCOS Symptoms?

The mechanisms through which probiotics may improve PCOS symptoms are being investigated. Probiotics are being investigated for their ability to:

Regulating Gut Microbiota – Probiotics may help restore microbial diversity, increasing beneficial bacteria and reducing harmful ones
Enhancing Insulin Sensitivity – Probiotics may improve insulin signaling, reducing fasting blood glucose and insulin resistance
Modulating Androgen Levels – Probiotic supplementation may reduce testosterone production by influencing gut-liver hormone metabolism
Reducing Chronic Inflammation – Probiotics help lower inflammatory markers like CRP and oxidative stress indicators
Supporting Weight Management – Some strains of Lactobacillus and Bifidobacterium have been linked to reductions in BMI and waist circumference

What the Research Shows

Multi-Strain Probiotics and PCOS Management

One randomized, double-blind, placebo-controlled study evaluated the impact of multi-strain probiotics in 104 women with PCOS (ages 18–40) over six months. The intervention contained strains of Lactobacillus acidophilus, L. rhamnosus, L. reuteri, L. plantarum, L. casei, L. fermentum, and Bifidobacterium bifidum. Both intervention and control groups received education on dietary and lifestyle modifications.

The probiotic group showed significant improvements in menstrual cycle regularity, testosterone levels, waist circumference, and overall quality of life compared to placebo.

Probiotics Combined with Vitamin D

Another randomized, double-blind, placebo-controlled trial examined the effects of vitamin D and probiotic co-supplementation in 60 women with PCOS. Participants received 50,000 IU of vitamin D every two weeks plus 8×10⁹ CFU/day of probiotics for 12 weeks. The strains included were Lactobacillus acidophilus, Bifidobacterium bifidum, Lactobacillus reuteri and Lactobacillus fermentum.

This combination led to significant reductions in testosterone levels, hirsutism, high-sensitivity C-reactive protein (hs-CRP), and oxidative stress markers, alongside improvements in mental health outcomes such as anxiety and depression

Probiotics vs. Metformin for PCOS

A randomized clinical trial compared probiotics (details of strains not provided), metformin, and their combination in 60 non-obese women with PCOS over 12 weeks. The study found that:

Menstrual cycle recovery rates were 40% in the probiotics group, 55% in the metformin group, and 80% in the combination group.
Ovulation rates were 30%, 55%, and 75% in the probiotics, metformin, and combination groups, respectively.
Both probiotics and metformin reduced insulin resistance, testosterone levels, and BMI, but their combination was most effective in improving metabolic and hormonal markers

Other studies

A systematic review and meta-analysis by Cozzolino and others evaluated nine randomized controlled trials (totaling 587 participants) on probiotic and synbiotic supplementation in PCOS. Results indicated that probiotic supplementation significantly improved fasting plasma glucose (FPG), fasting blood insulin (FBI), homeostasis model assessment of insulin resistance (HOMA-IR), body mass index (BMI), and serum testosterone levels. Synbiotics were more effective than prebiotics and probiotics alone.

Similarly, another systematic review and meta-analysis reviewed eight systematic reviews and confirmed that probiotics were beneficial for metabolic markers such as BMI, lipid profiles, and glucose homeostasis. However, the researchers emphasized the high variability in probiotic strains, dosages, and study durations, making it difficult to determine the optimal intervention.

Limitations of the Research

While the evidence supporting probiotic use in PCOS is promising, several limitations must be considered:

Variability in Probiotic Strains and Dosages: Different studies used different strains and dosages, making it difficult to establish a standard regimen
Short Study Durations: Most trials lasted between 8 to 24 weeks, which may not be long enough to assess long-term benefits
Small Sample Sizes: Many studies included fewer than 100 participants, limiting generalizability
High Heterogeneity in Outcome Measures: Different studies measured different PCOS parameters, making direct comparisons challenging

Conclusion: Should Dietitians Recommend Probiotics for PCOS?

The available evidence suggests that probiotics, particularly Lactobacillus and Bifidobacterium, may offer substantial benefits for individuals with PCOS, particularly in improving insulin resistance, inflammation, and hormonal imbalances.

This is an emerging area of research and more studies are needed to determine optimal probiotic strains and dosages.