Lower serum oestrogen concentrations associated with faster intestinal transit
S. J. Lewis; K. W. Heaton; R. E. Oakey; H. H. G. McGarrigle
British Journal of Cancer1997
Summary (paraphrased)
Forty healthy premenopausal volunteers were randomized to senna, loperamide, or wheat bran across menstrual cycles while whole-gut transit time, fecal beta-glucuronidase activity, stool pH, and serum estrogens were measured. Speeding transit with senna lowered serum oestrone sulphate and total and non-protein-bound oestrone, with wheat bran showing a similar trend; slowing transit with loperamide produced no significant change. The authors concluded that faster intestinal transit reduces serum estrogen concentrations, consistent with less time for colonic reabsorption of deconjugated estrogens.
Why it’s in the systems review
Powers' background material treats transit time as a lever on steroid exposure, and the corpus already holds a transit-time review — this 1997 human intervention is the primary study behind it and makes the link experimental rather than theoretical. It earns its place because it shows that a mundane gut parameter (transit speed) measurably changes circulating steroid levels, exactly the kind of individually variable exposure factor the causal-pathway search needs.