The gut and female fertility: What does the science say?

By Nikki Hancocks

- Last updated on GMT

Marharyta marko | Getty
Marharyta marko | Getty

Related tags Fertility Gut health Prebiotic Probiotic Lactobacillus microbiome Nutrition

There is a relationship between the microbiome and female reproductive health and while further research is required it appears lactobacillus supplements could support those with dysbiosis.

This was the message from Ro Huntriss, specialist fertility dietitian and founder of Fertility Dietitian UK clinic, during a women's gut health event hosted by Yakult last week (May. 1).

She explained to the audience of UK health and nutrition practitioners the many ways that nutrition and gut health can impact fertility.

“The gut microbiota significantly impacts the endocrine reproductive system by interacting with hormones such as oestrogen, androgens and insulin; therefore the gut microbiota can be implicated in conditions such as PCOS and endometriosis which are risk factors for infertility.”

What’s more, she noted research​ has found that the gut microbiome is different between fertile and infertile women but a causative link between dysbiosis and infertility has not been established.

Lactobacillus is one of the main bacteria in the vaginal microbiome of healthy women and its production of lactic acid prevents the overgrowth of potentially pathogenic yeast, bacteria and viruses, she explained. Whereas low levels of lactobacillus have been linked with early miscarriage​ and implantation failure​.

She explained research into microbiome-related therapies in the improvement of reproductive outcomes is still very much in its infancy but “we are seeing interesting results from emerging studies”.

For example, recent critical analysis of research​ suggested that hydrolysed guar gum (a prebiotic) may reduce dysbiosis and promote pregnancy rates and a lactobacillus probiotic may improve live birth rates in those with a history of recurrent miscarriage.

The 'pro-fertility diet'

A “pro-fertility diet“ – a Mediterranean style diet characterized by high intakes of fruits, vegetables, fish, and whole grains and low intakes of snacks, meats, and positively correlated with red blood cell folate - is associated with a 40% higher pregnancy rate​ for infertile couples undergoing IVF or ICSI (Intracytoplasmic sperm injection), as it can impact several parameters of​ fertility including; number of oocytes (ovary cells), sperm health, and ovarian stimulation.

Specifically, she noted the most important nutrients in this regard include: folate, to support egg and sperm quality, reduce risk of neural defects and support healthy ovulation; antioxidants such as vitamins C, E, selenium, and zinc to support implantation and progesterone levels; omega-3, improves egg and sperm quality, reduces inflammation and supports the gut microbiome; vitamin D supports ovulation and reduced risk of miscarriageand the gut microbiome; and vitamin B12 improves plantation ratea and reduces the risk of miscarriage.

“Imagine somebody having suffered a miscarriage, the impact that has on somebody and their family is so great. So when we start to see research that suggests something as simple as a probiotic can help this, the potential can be life-changing for individuals.”

However, she said there is conflicting research and she warned biotics may have no effect in someone with a perfectly balanced microbiome therefore “we don’t want to apply these as a blanket rule for everybody.”

She said further research is needed to discover if studies concluding a lack of impact of biotics have been a result of those participants already having a healthy microbiome.

Endometriosis and PCOS

Huntriss pointed out that the connection between the microbiome and hormones​ would suggest the gut could impact hormonal diseases such as endometriosis and PCOS.

“A 2020 systematic review​ found that probiotics and synbiotics seem to either have a positive effect or influence on metabolic, hormonal and inflammatory parameters," she noted. “They may also improve testosterone levels, decrease inflammation, and improve metabolic parameters consequently leading to an improvement in fertility in PCOS.”

Further research is now being done to assign certain strains to certain symptoms​, such as glucose and insulin balance, excess testosterone, and inflammation, “and that’s when things are going to become really useful”, she said.

Endometriosis is an inflammatory condition where uterine tissue grows outside the uterus and is largely impacted by levels of circulating estrogen​. 

“Women with endometriosis appear to have lower levels of lactobacillus in their microbiome and dysbiosis can lead to inflammation and increased circulating estrogen, both of which are a risk factor of endometriosis.”

She said there is a little research suggesting this strain of probiotic may support endometriosis symptoms but, again, further study is required and she believes this is a very promising avenue for symptom support.

“I’m going to go out there and say there is a relationship between the microbiome and female reproductive health," she concluded. "A probiotic containing lactobacillus could support fertility but we always need to think about these things on an individual level as it’s more likely to help people with dysbiosis.”

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