Our gut microbiota plays a major role in hormonal balance by regulating the reabsorption of our estrogens (about 40% of which pass through the intestine) and by harboring the production of 95% of our serotonin, a process that can be disrupted by inflammation.

noli's read

The idea that the gut influences estrogens is based on a real scientific concept called the "estrobolome," described notably in a review by Baker et al. (2017) published in *Maturitas* (based on observational studies). Certain bacteria do indeed produce enzymes that reactivate estrogens so they can be reabsorbed by the body, although the specific figure of 40% remains a general estimate. Regarding serotonin, it is accurate that nearly 90% to 95% of this molecule is produced in the gut, as confirmed by a study by Yano et al. (2015) in *Cell* (mechanistic evidence). However, it must be clarified that this intestinal serotonin does not directly cross the blood-brain barrier to affect mood, even though there is indirect communication with the brain. Finally, the fact that inflammation diverts tryptophan (the basic component of serotonin and melatonin) toward other pathways is a well-documented biochemical phenomenon, summarized by O'Mahony et al. (2015) in *Behavioural Brain Research*.

the sources

No named source held this one up — that absence is part of the verdict.