title: "Your Gut Microbiome and Testosterone: The Connection You're Probably Not Thinking About" description: "The gut-hormone axis: enterohepatic circulation of oestrogens, microbiome diversity, and practical dietary interventions for hormonal health." date: "2026-03-29" author: "Seb" category: "Nutrition & Hormones" tags: ["microbiome", "testosterone", "gut health", "oestrogen", "fibre", "diversity"] affiliateDisclosure: false
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Your gut bacteria produce a metabolite that determines how much oestrogen your body reabsorbs.
This is called the enterohepatic circulation of oestrogen, and it's a legitimate mechanism by which your microbiome can influence your testosterone/oestrogen balance.
This sounds scientific, but here's why it matters: if you have a healthy, diverse microbiome, you reabsorb less oestrogen, which improves your testosterone/oestrogen ratio. If your microbiome is dysfunctional, you reabsorb more oestrogen, which worsens your ratio.
This is emerging science with limited human data, but the mechanism is solid and the practical implications are actionable. This guide walks through what we know, what we're still learning, and what you can actually do about it.
The Enterohepatic Circulation of Oestrogen
Here's the mechanism:
Your liver conjugates (chemically modifies) oestrogen to make it water-soluble so your kidneys can excrete it. The conjugated oestrogen is dumped into your bile and flows into your intestines.
In your intestines, bacteria produce an enzyme called beta-glucuronidase. This enzyme deconjugates oestrogen—reverting it back to the unconjugated form, which is reabsorbed across your intestinal wall back into your bloodstream.
So oestrogen gets recycled.
The microbiome connection: Healthy, diverse bacteria produce the right amount of beta-glucuronidase. Dysbiotic bacteria (poor diversity, pathogenic dominance) produce too much beta-glucuronidase. More enzyme means more oestrogen reabsorption, which means higher circulating oestrogen.
The testosterone implication: Higher oestrogen suppresses testosterone production and increases conversion of testosterone to oestrogen. Lower oestrogen (from better microbiome-mediated excretion) preserves your testosterone/oestrogen ratio.
This is why microbiome health is relevant to hormonal health.
Microbiome Diversity and Testosterone
Observational research shows that men with lower microbiome diversity have lower testosterone levels. The correlation is real and consistent across studies.
The mechanism: Lower diversity correlates with dysbiosis (pathogenic imbalance). Dysbiosis is associated with:
- Increased systemic inflammation (which suppresses testosterone)
- Increased intestinal permeability ("leaky gut," though this term is controversial)
- Altered short-chain fatty acid production (butyrate is important for gut barrier integrity)
- Altered oestrogen metabolism (more beta-glucuronidase)
All of these can depress testosterone.
Important caveat: This is correlational data. We don't have randomised controlled trials proving that improving microbiome diversity increases testosterone in humans. But the mechanism is plausible and the biomarker associations are consistent.
What Destroys Your Microbiome
Before discussing what builds it, let's address what ruins it:
Antibiotics: Necessary sometimes, but they're indiscriminate killers. A course of antibiotics reduces diversity significantly. It takes months to recover fully.
Ultra-processed food: High sugar, low fibre, seed oils. These feed pathogenic bacteria and starve beneficial ones.
Chronic stress: Stress hormones alter gut bacteria composition directly.
Alcohol: Particularly in excess. Damages the gut barrier and alters bacterial composition.
Sleep deprivation: Poor sleep alters microbiome composition.
Medications: Particularly PPIs (proton pump inhibitors), which alter stomach acid and allow pathogenic colonisation.
Sedentary lifestyle: Movement supports bacterial diversity.
What Builds Microbiome Diversity
The primary lever is fibre.
Fibre is prebiotic. It's not digested by your enzymes—it passes through and is fermented by bacteria. This fermentation produces short-chain fatty acids (primarily butyrate), which feed the cells lining your gut and support barrier integrity.
Different bacteria ferment different types of fibre. To maximise diversity, you need variety.
The protocol: 30+ different plant sources per week.
This means 30+ different types of plant foods: vegetables, fruits, grains, legumes, nuts, seeds. Not 30 servings of the same food, but 30 different plants across the week.
Practically:
- Vegetables: Broccoli, spinach, carrots, sweet potato, peppers, tomatoes, onions, garlic, asparagus, kale (that's 10)
- Fruits: Apple, banana, orange, blueberries, strawberries, avocado (that's 6)
- Grains/legumes: Oats, brown rice, quinoa, lentils, chickpeas, black beans (that's 6)
- Nuts/seeds: Almonds, walnuts, flax seeds, chia seeds, pumpkin seeds (that's 5)
- Herbs/spices: Garlic, ginger, turmeric, basil, oregano (that's 5)
That's 32 different plant sources. Across a week, this is achievable with normal eating.
Why this matters: Each plant source has unique fibre chemistry. Carrots feed different bacteria than oats. Legumes feed different bacteria than berries. Diversity of input → diversity of microbiota.
Fermented Foods
Fermented foods contain live bacteria that can potentially colonise your gut (though most don't survive stomach acid).
Kefir: Fermented milk drink with multiple bacterial strains. Some evidence that regular consumption improves microbiome diversity.
Live yoghurt: Cultures listed on the label should include multiple strains. Avoid "yoghurt drinks" which are sugar bombs.
Sauerkraut: Fermented cabbage. Contains Lactobacillus species.
Miso: Fermented soybean paste. Contains beneficial bacteria.
Tempeh: Fermented soybean product. Contains beneficial bacteria plus complete protein.
Kombucha: Fermented tea. Has bacteria and yeasts, though some concern about contamination if homemade. Commercial versions are safer.
Evidence: Modest evidence that regular fermented food consumption improves microbiome markers and inflammation. Don't expect miracles, but it's a reasonable addition.
Practical: Include one fermented food daily. Kefir, live yoghurt, or sauerkraut with meals is simple.
The SIBO/Leaky Gut Connection
SIBO (Small Intestinal Bacterial Overgrowth): When bacteria proliferate in the small intestine (where they shouldn't be, they should be in the colon). Causes bloating, malabsorption, and can damage the intestinal barrier.
Leaky gut: Increased intestinal permeability, allowing bacterial lipopolysaccharides (LPS) to enter the bloodstream. Causes systemic inflammation.
Both can be consequences of dysbiosis and can suppress testosterone through systemic inflammation.
How to know if you have this: Symptoms are bloating, gas, abdominal discomfort, food intolerances, general malaise. Testing is available (breath testing for SIBO, intestinal permeability markers) but is not standard.
How to address it: The same protocol as above—increase fibre diversity, add fermented foods, reduce ultra-processed food, manage stress, sleep well. If you suspect SIBO, work with a functional medicine practitioner who can test and treat appropriately.
The Practical Protocol
Establish a baseline: How diverse is your diet now? Spend a week tracking plant foods and see where you land. Are you at 10 different plants per week? 5? 20?
Build toward 30: Add new plant foods weekly. If you normally eat 5 vegetables, add 2 new ones next week. If you never eat legumes, start with lentils in soups.
Add fermented foods: One serving daily. Kefir, yoghurt, sauerkraut, or miso.
Reduce processed food: Ultra-processed foods are killing your microbiome. Not necessarily all-or-nothing, but trend toward whole foods.
Manage stress: Stress hormones suppress beneficial bacteria. Sleep, movement, and stress management all support microbiome health.
Limit antibiotics: When prescribed, they're necessary. But casual use (antibacterial soaps, etc.) is pointless and harmful to your microbiome.
Fibre gradual increase: If you currently eat low fibre, increasing suddenly causes bloating and gas. Add fibre gradually over 2–4 weeks to allow bacterial adaptation.
Microbiome Testing
Direct microbiome testing (16S sequencing, shotgun metagenomic sequencing) is available through commercial labs. Cost is £150–300 per test.
Useful information: Bacterial diversity scores, specific bacterial taxa, functional potential.
Practical value: Tells you if you're actually diverse. Baseline + remeasure in 3–6 months shows if your interventions are working.
Is it necessary? No. The interventions (fibre diversity, fermented foods, stress management, sleep) are beneficial regardless. Testing can be motivating if you like data.
The Honest Assessment
What we know for sure: Microbiome diversity is associated with better health markers. Fibre and fermented foods improve microbiome diversity. Poor microbiome diversity is associated with dysbiosis and systemic inflammation.
What's plausible: A dysbiotic microbiome could suppress testosterone through inflammation and altered oestrogen metabolism.
What we don't know: Whether improving microbiome diversity specifically increases testosterone in healthy men. The human data is limited.
Bottom line: A healthy microbiome is important for general health and probably for hormonal health. The interventions (eat more fibre, more plants, add fermented foods) are beneficial anyway and cost almost nothing. Even if the testosterone-specific benefit is modest, the general health benefit is substantial.
The Practical Minimum
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Eat 30+ different plant sources per week. Vegetables, fruits, grains, legumes, nuts, seeds, herbs.
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Add one fermented food daily. Kefir, yoghurt, or sauerkraut.
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Reduce ultra-processed foods. Doesn't need to be all-or-nothing, but trend toward whole foods.
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Manage stress and sleep. These affect microbiome composition directly.
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Avoid unnecessary antibiotics. When prescribed, they're necessary. Otherwise, avoid.
That's the protocol. It's not rocket science. It's basic health that happens to support microbiome diversity and (probably) testosterone health.
This guide covers emerging science on the microbiome-hormone axis. Mechanisms are plausible, but human evidence is limited. Recommendations are grounded in general health benefits regardless of testosterone-specific effects.