Women as Bacterial Hosts

Yep. It’s true.

Men and women are distinctly different from one another and studies are continuing to find that these differences affect the gut as well. Most science suggests the reason for these differences is due to the different hormones at play.  

The female reproductive system is incredible: a reoccurring cycle that requires detailed regulation with many factors. Ladies have a natural ebb and flow of hormones that occur every cycle, making menstruation and ultimately reproduction possible. This fluctuation has an effect on the entire person, including the gut microbiome.  


First, let’s take a look at the three primary hormones involved within the female host. These key players include follicle stimulating hormones, luteinizing hormones, estrogen, and progesterone.  

Follicle stimulating hormones

These hormones are produced in the pituitary gland (located at the base of the brain) and dropped into the bloodstream. Using this passageway, they make their way down to the ovaries to do their work. This follicle-stimulating hormone does exactly what it sounds like! It stimulates the growth of follicles on the ovary to create a space for an egg to grow.  

Luteinizing hormones

These hormones are also produced in the pituitary gland. They play a critical role during two parts of menstruation. In weeks one and two, they stimulate ovarian follicles just created by the follicle-stimulating hormones, to produce another hormone called estrogen, which is also required for the maturation of an egg. Around day 14, a large surge in luteinizing hormone causes the matured egg to tear away from the follicle and begin its journey through the fallopian tubes.  


Estrogen is produced in the ovaries and controlled by hormones released by both the hypothalamus in the brain and the pituitary gland. These hormone levels vary greatly over the course of a cycle and are highest at ovulation and lowest at menstruation. This is because of the role it plays in causing the egg to mature and be released. Estrogen also plays a key role in causing the lining of the uterus to thicken in the event an egg is fertilized and needs a place to implant and grow. 


Progesterone is released in the second half of menstruation by a specialized area in the ovary called the corpus luteum. (The corpus luteum is the exposed area on the ovary after the egg tears away from the follicle.) The role progesterone plays is to prepare the body for pregnancy and maintain the pregnancy if an egg is fertilized. If the egg is not fertilized, this area deteriorates and the production of progesterone drops quickly, causing major fluctuations. After the placenta has been established in the event of a pregnancy, it takes over the progesterone production, producing up to 40x more than the normal amount! After delivery, this large amount of progesterone production is stopped, causing many of the negative side effects women to experience following pregnancy. 

woman losing hair after pregnancy 

Hormone Fluctuations

Many women experience GI discomfort at various stages of the menstruation cycle. Loose stools, bloating, abdominal discomfort, and constipation are common complaints of women of child-bearing years. This is likely due to the dramatic fluctuations in hormones.  

Progesterone has anti-inflammatory properties that are of benefit during pregnancy. It is suspected that due to these properties, progesterone decreases intestinal permeability during pregnancy (a good thing!). This means the tight junctions in the gut lining are compressed together, securing the barrier between the inside of the body (the gut, blood vessels, and lymph system) and the outside world.  

Estrogen appears to also have an effect on mucosal permeability. The proper balance of progesterone and estrogen is required for the most beneficial gut/hormone interaction. Estrogen dominance is exactly what it sounds like: the body is producing too much estrogen and not enough progesterone. It is linked to many symptoms including constipation, acne, weight gain, and depression.  

Things are always changing for the female – hormones not only fluctuate on a monthly cycle; changes occur throughout the lifespan. After living the majority of life with the support of these hormones, menopause arrives and brings a host of changes. 

woman in menopause


Menopause gradually ends the regular monthly flow of hormones. Without these hormones, all of the areas regulated by them are disturbed and have to establish a new normal. This includes the gut microbiome. Some women experience many symptoms of menopause, while others have few. Although there are many things that cannot be changed to aid in this transition, we can support the gut and the two-way communication the gut microbiome is a part of. Support gut health with high fiber foods, exercise, adequate sleep, stress management, and a high-quality, diverse probiotic


Body Awareness

If you find yourself on a yo-yo of loose stools and constipation, try taking the time to compare the ups and downs with the menstruation cycle. Just like most things in relation to the gut, communication and disruption go both ways. Gut microbiome disruptions may play a role in hormone imbalances, while hormone imbalances may play a role in gut microbiome disruptions.  

The human body is so creative and complex. There is so much communication that goes from one part of the body to another. Instead of using words, hormones, neurons, and even metabolites produced by gut bacteria are used to get the message where it needs to be.  



The content in this post is not intended to be professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health providers with any questions you may have regarding a medical condition. 


Written by Lorilyn Van Dyke, Entegro Health



Kim, Y., Unno, T., Kim, B., & Park, M. (2029). Sex Differences in Gut Microbiota. World Journal of Men’s Health, 48-60. doi:10.5534/wjmh.190009 

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Society for Endocrinology. (n.d.). Hormones Home. Retrieved April 21, 2021, from https://www.yourhormones.info/hormones/ 

McCormick, K. (n.d.). A Lifetime of Progesterone by Women’s International Pharmacy. Retrieved April 22, 2021, from https://www.womensinternational.com/blog/portfolio-items/progesterone/ 

Zhoau, Z., Bian, C., Luo, Z., Guille, C., Ogunrinde, E., Wu, J., . . . Jiang, W. (2019). Progesterone decreases gut permeability through upregulating occludin expression in primary human gut tissues and Caco-w cells. Scientific Reports, 9. doi:https://doi.org/10.1038/s41598-019-44448-0