HEMOPHILIA: …Another form, fairly common on poorer worlds with limited vegetation, is associated with avitaminosis. Survivors of dysentery and similar illnesses, unable to replenish their lost supplies of intestinal bacteria, have no way of producing vitamin K, with the result that…
…It has been suggested (Pawk and Bollinsh, 1007) that a future, more perfectly evolved humanity will possess a small sac attached to the large intestine, analogous to the "appendix" found in certain small herbivores, which would seal and store bacteria during severe diarrheic episodes. No such organ, however, has yet been observed in any living human body…
–ENCYCLOPEDIA GALACTICA
Disclaimer: If I were Isaac Asimov, would I be writing things like Sacred Host?