Gut health & Fertility: Is there a connection?

More than ever before, we're understanding that fertility is not just a stand-alone area — it's usually a signal or a sign of something else going on in the body.

What we're seeing in research is that the gut and brain are more closely involved in the whole reproductive system than previously thought — including hormone signalling, insulin sensitivity, inflammation, and the bacteria found in reproductive organs like the vagina. This connection has been coined the "gut microbiota-gonadal axis" by researchers published in Frontiers in Immunology (Ashonibare et al., 2024).

Why is our gut so important?

Our gut is host to trillions of bacteria, viruses, fungi, and other microorganisms. When we talk about "the gut," it's mostly in reference to the large intestine — the ultimate host of the most — although microbiomes are also found in the stomach and small intestine. Some lesser-known sites that host these microorganisms include the skin, vagina, penis, and mouth. In fact, microbiome cells make up roughly half of all the cells in our body (Sender et al., 2016).

What does our gut microbiome do?

A healthy gut microbiome plays a remarkable number of roles in the body. It acts as a shield against toxins and pathogens, breaks down tough-to-digest fibres, helps absorb and synthesise vitamins and minerals, regulates the immune system and produces chemicals that influence our mood and how our brain functions.

The diversity and composition of your gut bacteria matters enormously. Research has found that a more robust and diverse microbiome — featuring bacteria such as Akkermansia, Faecalibacterium, and Butyrivibrio species — is associated with lower rates of metabolic disorders. On the flip side, gut dysbiosis (an imbalance of gut bacteria) is characterised by an overgrowth of pro-inflammatory species that can drive inflammation across the entire body — including the reproductive system (Le Chatelier et al., 2013).

What factors play into the composition of gut microbiome?

• Age

• Genetic predisposition

• Diet

• Physical activity

• Stress and mood

• Exposure to toxins (and endocrine-disrupting chemicals)

Ok so, how does this relate to fertility and my hormones?

This is where it gets really interesting. Gut dysbiosis doesn't stay in the gut. Through a number of mechanisms (including estrobolome - we’ll talk about this next), what's happening in your gut can directly shape your hormonal environment and your reproductive health.

What is Estrobolome?

The estrobolome refers to a specific collection of gut microbes capable of metabolising oestrogens. These bacteria produce an enzyme called β-glucuronidase, which plays a central role in how your body recycles and eliminates oestrogen (Baker et al., 2017).

Here's how it works:

1. Oestrogen is processed by the liver and conjugated (essentially deactivated)

2. It’s then sent to the gut for elimination

3. The estrobolome then deconjugates a portion of this oestrogen — that's right, it gets recycled — allowing it to be reabsorbed back into circulation via a process called enterohepatic recirculation.

4. After being recycled and used, it eventually gets eliminated (usually through our poo).

   
   In a healthy, balanced microbiome, this process is tightly regulated, maintaining just the right amount of circulating oestrogen.
   
   When the microbiome is disrupted, β-glucuronidase activity can swing in either direction. Too high, and more oestrogen is reabsorbed into circulation — a state of oestrogen dominance that can drive conditions like endometriosis, fibroids, and irregular cycles. Too low, and insufficient oestrogen recirculates — affecting ovulation and implantation.
   
   For women trying to conceive, both extremes create a hormonal environment that makes conception harder.

   So, What About for fellas?

   
   This is a conversation that doesn't happen nearly enough.
   
   Men have oestrogen too — and it matters for fertility. In men, oestrogen balance supports sperm maturation and libido. But beyond oestrogen, gut dysbiosis has been directly linked to male reproductive function through what researchers have termed the "androbactome" — the collection of gut microbes involved in androgen metabolism and testicular function (Kaltsas et al., 2025). Changes in gut microbiome composition have been associated with reduced testosterone production, impaired spermatogenesis (the process of sperm cell development), and higher levels of oxidative stress — all of which negatively affect sperm quality and count. Certain microbial species are associated with higher oxidative reactive potential, and studies have demonstrated a direct link between this and abnormal semen parameters in infertile men (Kaltsas et al., 2025).
   
   So when we talk about gut health and fertility, both partners need to be part of the conversation.
   
   
   

   What This Means in Practice

   
   The good news is that the gut is one of the most modifiable factors in your fertility. Food is where a great deal of this begins.
   
   A diet rich in diverse whole foods, fermented foods and key fertility nutrients supports a healthier microbiome — and by extension, a better hormonal environment for conception. But it's important to note that this looks different for everyone. Conditions like endometriosis, PMOS, SIBO, IBD, coeliac disease, and histamine intolerance all change what gut-supportive eating looks like in practice. What benefits one person may worsen symptoms in another.
   
   This is where personalised nutrition guidance makes a real difference.

   
   A Note on the Evidence
   

   I always like to put this caveat in - the gut-fertility field is evolving rapidly. Much of the research has been conducted in animal models, and large-scale human RCTs are still catching up. That said, the evidence is strong, biologically plausible, and increasingly supported by observational human and animal studies. This is a legitimate and emerging area of fertility nutrition.
   

   Working with a Dietitian

   
   If you're planning to or actively trying to conceive and you're also managing gut symptoms, irregular cycles, unexplained infertility, or a diagnosis that intersects both systems — it’s worth exploring the gut-fertility connection with a dietitian who’s area of interest lies in both specialisations.
   
   This is exactly the kind of work we do — for women and for couples. Reach out to book a discovery call and find out how we can support you both.

   
   References

Ashonibare, V.J., Akorede, B.A., Ashonibare, P.J., Akhigbe, T.M. and Akhigbe, R.E. (2024) 'Gut microbiota-gonadal axis: the impact of gut microbiota on reproductive functions', Frontiers in Immunology, 15, 1346035. doi: 10.3389/fimmu.2024.1346035.

Baker, J.M., Al-Nakkash, L. and Herbst-Kralovetz, M.M. (2017) 'Estrogen-gut microbiome axis: Physiological and clinical implications', Maturitas, 103, pp. 45–53. doi: 10.1016/j.maturitas.2017.06.025.

Le Chatelier, E., Nielsen, T., Qin, J., Prifti, E., Hildebrand, F., Falony, G., Almeida, M., Arumugam, M., Batto, J.M., Kennedy, S. et al. (2013) 'Richness of human gut microbiome correlates with metabolic markers', Nature, 500, pp. 541–546. doi: 10.1038/nature12506.

Kaltsas, A., Giannakodimos, I., Markou, E., Stavropoulos, M., Deligiannis, D., Kratiras, Z. and Chrisofos, M. (2025) 'The androbactome and the gut microbiota-testis axis: a narrative review of emerging insights into male fertility', International Journal of Molecular Sciences, 26(13), 6211. doi: 10.3390/ijms26136211.

Sender, R., Fuchs, S. and Milo, R. (2016) 'Revised estimates for the number of human and bacteria cells in the body', PLOS Biology, 14(8), e1002533. doi: 10.1371/journal.pbio.1002533.

Sidhu, M. and van der Poorten, D. (2017) 'The gut microbiome', Australian Family Physician, 46(4), pp. 206–211. Available at: https://www.racgp.org.au/afp/2017/april/the-gut-microbiome (Accessed: 9 June 2026).