Hormones and Gut Health

Why Hormone Levels Depend Partly on the Gut

Hormones are made by glands and disposed of by the liver. That's the version most people are given, and it leaves out a step. When the liver finishes with a hormone it tags it chemically and sends it into the gut for removal. Certain gut bacteria can cut that tag off, freeing the hormone to be reabsorbed instead of excreted. So how much of a hormone is circulating depends partly on which bacteria are present. Other bacteria go further and manufacture hormones outright.

Recycling, manufacture and calibration

Recycling is the best-documented route. An enzyme called beta-glucuronidase, produced by a range of common gut bacteria, removes the disposal tag from oestrogen and returns it to circulation. In 51 adults, total oestrogen in urine tracked closely with how rich and varied the gut bacteria were, with correlations of at least 0.50 in men and postmenopausal women. Across 2,300 people, that enzyme capacity was reduced after the menopause, alongside a bacterial community that had shifted to resemble men's more than younger women's.

Manufacture is the more surprising route. Some gut bacteria convert androgen precursors into active testosterone. Others convert stress hormones into compounds in the progesterone family, a reaction that only runs when hydrogen gas from fibre fermentation is present. In mice, transferring gut bacteria from adult males into young females raised the recipients' testosterone directly.

Calibration is the third. Mice raised without gut bacteria release substantially more stress hormone under pressure than normal mice, and giving them a single bacterial species early in life corrects it. Arriving later works much less well, which points to something built rather than adjusted.

The thyroid works differently again. Low thyroid hormone slows the gut, and bacterial overgrowth in the small intestine was present in 33% of people with a history of an underactive thyroid against 15% of those without.

Source: Fecal microbial determinants of fecal and systemic estrogens and estrogen metabolites: a cross-sectional study

Source: Menopause Is Associated with an Altered Gut Microbiome and Estrobolome

Source: Sex differences in the gut microbiome drive hormone-dependent regulation of autoimmunity

What this means for you

Symptoms people attribute to hormones, including persistent fatigue, cycle changes, unexplained weight change or low mood, have specific testable causes, so a doctor and a blood test are the useful first step rather than a supplement. In addition, the research above shows gut bacteria determining how much of a hormone is recycled rather than excreted, manufacturing hormones outright in some cases, and helping calibrate the stress response early in life. A varied, plant-rich diet supports the same gut bacteria this research ties to steadier hormone handling. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.

Explore hormone topics on this page

The panels on this page cover different hormones and different mechanisms, so the evidence for one doesn't carry over to another.

Estrogen balance and menopause hormones concern the recycling enzyme and how its capacity changes with age. Testosterone and progesterone concern bacteria that manufacture hormones themselves.

Thyroid problems and Hashimoto's concern movement, absorption and immune training rather than hormone chemistry. Hormone imbalance covers the shared routes running underneath all of them.

Use the panels on this page to find the one relevant to you.