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Gut Bacteria

Our gut microbiota, or gut microorganisms, total 10-100 trillion microbial cells, making up about 2kg of weight in the gut (1). Typically, there are 1000 bacterial phenotypes and 1200 viral phenotypes. Whilst its composition is fairly well established by the time we are 5 years old, the microbiota is not completely static and will change in relation to diet and disease (1). In a healthy diverse gut, the main role of these bacteria is to salvage energy from the non-digestible dietary components (fiber) as they pass through our colon, producing beneficial short chain fatty acids (SCFA's) that our colons cells use for nutrients. But this is only the start - the presence of these bacteria, and the resulting SCFA, actually can have much more wide reaching health benefits for us:

  • They optimise our immune system, allowing us to react to pathogenic bacteria whilst tolerating beneficial bacteria

  • They maintain our metabolism, keeping blood sugar and lipids in check

  • They reduce blood pressure and lower cholesterol

  • They act in cell signaling to affect our appetite and fullness

  • They support and protect our brain function, which helps with anxiety and mood

  • They help maintain the gut wall integrity

  • They increase stool frequency and consistency (so useful for helping those with diarrhoea or constipation)(2)

  • They synthesize vitamins for us to absorb, such as B12 and K

  • They regulate circulating oestrogen

Diet, in particular, makes up about 20% of the differences that are seen between peoples microbiota and the quality and variety of your diet has a marked impact on the different species and diversity of bacteria that are present (3). When this diversity is poor (commonly due to the typical Western diet or exclusion diets) then the microbiota is less flexible and unbalanced, which can lead to disease.

Metabolic health and the microbiota

If your gut is in a state of dysbiosis or imbalance, then there is a depletion of mucus around the colon cells and the gut wall integrity is reduced - sometimes called a 'leaky gut'. This leakiness allows pathogenic and opportunistic bacteria to enter and introduce bacterial lipopolysaccharides (LPS) into our body (3). This results in inflammation and an increased risk of insulin resistance (leading to type 2 diabetes). In fact a leaky gut has also been linked to obesity and non-alcoholic fatty liver disease (NAFLD) too. Various studies have found that the use of specific single bacterial stains (and combinations of strains) can affect parameters including our visceral and subcutaneous fat, our  weight, our blood pressure and our harmful cholesterol. Whilst this science is in its infancy for creating standardized clinical recommendations for metabolic health, there is much promise in the use of probiotics (live bacteria) and prebiotics (food components to increase bacterial diversity) to help in the reduction of metabolic risk factors (4).

Menopausal health and the microbiota

Low levels of circulating oestrogen during the various menopausal stages can affect many areas of a women's health. The gut microbiota play an important role to regulate circulating oestrogen by secreting β-glucuronidase, an enzyme that converts oestrogen into its active form, before it is absorbed and then transported around our body in the blood stream to where it is needed (5). If the gut is impaired through dysbiosis then less oestrogen conversion occurs and there is less circulating in the body, which has a knock on effect for endometriosis, polycystic ovary syndrome, cancer, obesity, metabolic syndrome, endometrial hyperplasia, fertility, cardiovascular disease and cognitive function (5). 

Diet, probiotics and prebiotics can be used to correct this dysbiosis and potentially help with a variety of menopausal symptoms including vaginal disorders (urinary tract infections, vaginosis, vaginal dryness), gastrointestinal discomfort, mood disorders and weight gain. 


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(1) Ursell L, Metcalf J, Parfrey L et al. Defining the Human Microbiome Nutr Rev. 2012;70(Suppl 1):S38–S44 - https://doi. 10.1111/j.1753-4887.2012.00493.

(2) Zhang S, Wang R, Li D et al. Role of gut microbiota in functional constipation. Gastroenterology Report 2021;9(5):392–401 -

(3) Green M, Arora K, Prakash S. Microbial Medicine: Prebiotic and Probiotic Functional Foods to Target Obesity and Metabolic Syndrome. Int. J. Mol. Sci. 2020;21(8):2890 -

(4) Mazloom K, Siddiqi I, Covasa M. Probiotics: How Effective Are They in the Fight against Obesity? Nutrients 2019;11(2):258 -

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

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