MTOR and Diarrhea: Abnormalities in the tryptophan-kynurenine-niacin pathway are also associated with intestinal inflammation, including during response to intestinal pathogens.18 19 In animal models, an inability to transport tryptophan into enterocytes results in diarrhoea, while provision of nicotinamide (a form of niacin) partly restores function of mTOR in enterocytes, increasing secretion of antimicrobial peptides and reducing diarrhoea,18 19 suggesting effects on diarrheal pathogens.